Embedded C - Day 2

Team Emertxe
C
Come let's see how deep it is!!
Day 2

Embedded C
Functions – What?
An activity that is natural to or the purpose of a person or
thing.
"bridges perform the function of providing access across water"
A relation or expression involving one or more variables.
"the function (bx + c)"
●
In programing languages it can something which performs a
specific service
●
Generally it can have 3 parameters like
– Input
– Operation
– Output
Source: Google

Embedded C
Functions – What?
Input
Output
f(x) = x + 1
x
Output
x + 1
2
3
2 + 1
x = 2

Embedded C
Functions – How to write
Syntax
return_data_type function_name(arg_1, arg_2, ..., arg_n)
{
/* Function Body */
}
Example
int foo(int arg_1, int arg_2)
{
}
Return data type as int
First parameter with int type
Second parameter with int type

Embedded C
Functions – How to write
y = x + 1
int foo(int x)
{
int ret = 0;
ret = x + 1;
return ret;
}
Example
Formal argumentsReturn from function

Embedded C
Functions – How to call
#include <stdio.h>
int main()
{
int x, y;
x = 2;
y = foo(x);
printf(“y is %dn”, y);
return 0;
}
Example
int foo(int x)
{
int ret = 0;
ret = x + 1;
return ret;
}
The function call

Embedded C
Functions – Why?
●
Re usability
– Functions can be stored in library & re-used
– When some specific code is to be used more than once, at different
places, functions avoids repetition of the code.
●
Divide & Conquer
– A big & difficult problem can be divided into smaller sub-problems
and solved using divide & conquer technique
●
Modularity can be achieved.
●
Code can be easily understandable & modifiable.
●
Functions are easy to debug & test.
●
One can suppress, how the task is done inside the function,
which is called Abstraction

Embedded C
Functions – A complete look
#include <stdio.h>
int main()
{
int num1 = 10, num2 = 20;
int sum = 0;
sum = add_numbers(num1, num2);
printf(“Sum is %dn”, sum);
return 0;
}
Example
int add_numbers(int num1, int num2)
{
int sum = 0;
sum = num1 + num2;
return sum;
}
The main function
The function call
Actual arguments
Formal arguments
`
Formal arguments
Return type
Formal argumentsReturn from function
Formal argumentsFunction

Embedded C
Functions – Ignoring return value
#include <stdio.h>
int main()
{
int num1 = 10, num2 = 20;
int sum = 0;
add_numbers(num1, num2);
return 0;
}
Example
{
int sum = 0;
sum = num1 + num2;
return sum;
}
Ignored the return from function
In C, it is up to the programmer to
capture or ignore the return value

Embedded C
Function and the Stack
P1
P2
P3
.
.
.
P1
Pn-1
Pn
RAM
Stack
Code Segment
Initialized
Heap
.BSS
(Uninitialized)
Command Line
Arguments
Hole
Data
Segment
Memory Layout
Local Variables
Return Address
Parameter List
Stack
Frame

Embedded C
Functions – Parameter Passing Types
Pass by Value Pass by reference
●
This method copies the actual
value of an argument into the
formal parameter of the function.
●
In this case, changes made to the
parameter inside the function have
no effect on the actual argument.
●
This method copies the address of
an argument into the formal
parameter.
●
Inside the function, the address is
used to access the actual
argument used in the call. This
means that changes made to the
parameter affect the argument.

Embedded C
Functions – Pass by Value
#include <stdio.h>
int add_numbers(int num1, int num2);
int main()
{
int num1 = 10, num2 = 20, sum;
return 0;
}
Example
{
int sum = 0;
sum = num1 + num2;
return sum;
}

Embedded C
Functions – Pass by Value
#include <stdio.h>
void modify(int num1);
int main()
{
int num1 = 10;
printf(“Before Modificationn”);
printf(“num1 is %dn”, num1);
modify(num1);
printf(“After Modificationn”);
printf(“num1 is %dn”, num1);
return 0;
}
Example
void modify(int num1)
{
num1 = num1 + 1;
}

Embedded C
Functions – Pass by Reference
#include <stdio.h>
void modify(int *iptr);
int main()
{
int num = 10;
printf(“num1 is %dn”, num);
modify(&num);
return 0;
}
Example
void modify(int *iptr)
{
*iptr = *iptr + 1;
}
Shell
(loader)
./a.out
main .text
modify .text

Embedded C
#include <stdio.h>
int main()
{
int num = 10;
modify(&num);
return 0;
}
Example
{
*iptr = *iptr + 1;
}
Shell
(loader)
./a.out
main .text
modify .text
1
num = 10
Return Address
to caller
1000
1

Embedded C
#include <stdio.h>
int main()
{
int num = 10;
modify(&num);
return 0;
}
Example
{
*iptr = *iptr + 1;
}
Shell
(loader)
./a.out
main .text
modify .text
1
num = 10
Return Address
to caller
1
1000
Return Address
to main
iptr = 1000
2
2
2000
&

Embedded C
#include <stdio.h>
int main()
{
int num = 10;
modify(&num);
return 0;
}
Example
{
*iptr = *iptr + 1;
}
Shell
(loader)
./a.out
main .text
modify .text
1
num = 11
Return Address
to caller
1
1000
Return Address
to main
iptr = 1000
2
2
2000
*

Embedded C
Functions – Pass by Reference - Advantages
●
Return more than one value from a function
●
Copy of the argument is not made, making it fast, even
when used with large variables like arrays etc.
●
Saving stack space if argument variables are larger
(example – user defined data types)

Embedded C
Functions – Passing Array
●
As mentioned in previous slide passing an array to
function can be faster
●
But before you proceed further it is expected you are
familiar with some pointer rules
●
If you are OK with your concepts proceed further, else
please know the rules first

Embedded C
#include <stdio.h>
void print_array(int array[]);
int main()
{
int array[5] = {10, 20, 30, 40, 50};
print_array(array);
return 0;
}
Example
void print_array(int array[])
{
int i;
for (i = 0; i < 5; i++)
{
printf(“Index %d has Element %dn”, i, array[i]);
}
}

Embedded C
#include <stdio.h>
void print_array(int *array);
int main()
{
int array[5] = {10, 20, 30, 40, 50};
print_array(array);
return 0;
}
Example
void print_array(int *array)
{
int i;
for (i = 0; i < 5; i++)
{
printf(“Index %d has Element %dn”, i, *array);
array++;
}
}

Embedded C
#include <stdio.h>
void print_array(int *array, int size);
int main()
{
int array[5] = {10, 20, 30, 40, 50};
print_array(array, 5);
return 0;
}
Example
void print_array(int *array, int size)
{
int i;
for (i = 0; i < size; i++)
{
printf(“Index %d has Element %dn”, i, *array++);
}
}

Embedded C
Functions – Returning Array
#include <stdio.h>
int *modify_array(int *array, int size);
void print_array(int array[], int size);
int main()
{
int array[5] = {10, 20, 30, 40, 50};
int *iptr;
iptr = modify_array(array, 5);
print_array(iptr, 5);
return 0;
}
Example
void print_array(int array[], int size)
{
int i;
for (i = 0; i < size; i++)
{
printf(“Index %d has Element %dn”, i, array[iter]);
}
}
int *modify_array(int *array, int size)
{
int i;
for (i = 0; i < size; i++)
{
*(array + i) += 10;
}
return array;
}

Embedded C
Functions – Returning Array
#include <stdio.h>
int *return_array(void);
void print_array(int *array, int size);
int main()
{
int *array_val;
array_val = return_array();
print_array(array_val, 5);
return 0;
}
Example
void print_array(int *array, int size)
{
int i;
for (i = 0; i < size; i++)
{
printf(“Index %d has Element %dn”, i, array[i]);
}
}
int *return_array(void)
{
static int array[5] = {10, 20, 30, 40, 50};
return array;
}

Embedded C
Functions – Recursive
●
Recursion is the process of repeating items in a self-similar
way
●
In programming a function calling itself is called as recursive
function
●
Two steps
Step 1: Identification of base case
Step 2: Writing a recursive case

Embedded C
Functions – Recursive – Example
#include <stdio.h>
/* Factorial of 3 numbers */
int factorial(int number)
{
if (number <= 1)
{
return 1;
}
else
{
return number * factorial(number – 1);
}
}
int main()
{
int result;
result = factorial(3);
printf(“Factorial of 3 is %dn”, result);
return 0;
}
Example

Embedded C
Functions – Recursive – Example Flow
Shell
(loader)
./a.out
Return Address
to main
2
number = 3
2
number != 1
number * factorial(number - 1)
3 * factorial(3 - 1)
3
4
number = 2
Return Address
to factorial3
number != 1
number * factorial(number - 1)
2 * factorial(2 - 1)
number = 1
Return Address
to factorial4 number == 1
result
Return Address
to caller
1 factorial(3)
Main .text
factorial .text
1
Stack Frames Value with calls

Embedded C
Functions – Recursive – Example Flow
Shell
(loader)
./a.out
Return Address
to main
2
number = 3
2
Returns 3 * 2 to the caller
3
number = 2
Return Address
to factorial3 Returns 2 * 1 to the caller
number = 1
Return Address
to factorial4 returns 1 to the caller
result
Return Address
to caller
1 Gets 6 a value
Main .text
factorial .text
1
Stack Frames Results with return
4

Embedded C
Functions – Function Pointers
●
A variable that stores the pointer to a function.
●
Chunk of code that can be called independently and is
standalone
●
“Registering” a piece of code and calling it later when
required
Syntax
return_datatype (*foo)(datatype, ...);

Embedded C
Functions – Function Pointers
#include <stdio.h>
int add(int num1, int num2)
{
return num1 + num2;
}
int main()
{
int (*function)(int, int);
function = add;
printf(“%dn”, function(2, 4));
return 0;
}
Example
#include <stdio.h>
void run_at_exit(void)
{
printf(“Exitingn”);
}
int main()
{
printf(“In Main Functionn”);
atexit(run_at_exit);
return 0;
}
Example

Embedded C
Functions – Variadic
●
Variadic functions can be called with any number of
trailing arguments
●
For example,
printf(), scanf() are common variadic functions
●
Variadic functions can be called in the usual way with
individual arguments
Syntax
return_data_type function_name(parameter list, ...);

Embedded C
Functions – Variadic – Definition & Usage
●
Defining and using a variadic function involves three steps:
Step 1: Variadic functions are defined using an ellipsis (‘…’) in
the argument list, and using special macros to access the
variable arguments.
Step 2: Declare the function as variadic, using a prototype
with an ellipsis (‘…’), in all the files which call it.
Step 3: Call the function by writing the fixed arguments
followed by the additional variable arguments.
int foo(int a, ...)
{
/* Function Body */
}
Example

Embedded C
Functions – Variadic – Argument access macros
●
Descriptions of the macros used to retrieve variable
arguments
●
These macros are defined in the header file stdarg.h
Type/Macros Description
va_list The type va_list is used for argument pointer variables
va_start This macro initializes the argument pointer variable ap to
point to the first of the optional arguments of the current
function; last-required must be the last required argument to
the function
va_arg The va_arg macro returns the value of the next optional
argument, and modifies the value of ap to point to the
subsequent argument. Thus, successive uses of va_arg return
successive optional arguments
va_end This ends the use of ap

Embedded C
Functions – Variadic – Example
#include <stdio.h>
int main()
{
int ret;
ret = add(3, 2, 4, 4);
printf(“Sum is %dn”, ret);
ret = add(5, 3, 3, 4, 5, 10);
printf(“Sum is %dn”, ret);
return 0;
}
Example
int add(int count, ...)
{
va_list ap;
int iter, sum;
/* Initialize the arg list */
va_start(ap, count);
sum = 0;
for (iter = 0; iter < count; iter++)
{
/* Extract args */
sum += va_arg(ap, int);
}
/* Cleanup */
va_end(ap);
return sum;
}

Embedded C
Pointers – Pitfalls – Segmentation Fault
●
A segmentation fault occurs when a program attempts to
access a memory location that it is not allowed to access, or
attempts to access a memory location in a way that is not
allowed.
#include <stdio.h>
int main()
{
int num = 0;
printf(“Enter the numbern”);
scanf(“%d”, num);
return 0;
}
Example
#include <stdio.h>
int main()
{
int *num = 0;
printf(“num = %dn”, *num);
return 0;
}
Example

Embedded C
Pointers – Pitfalls – Dangling Pointer
●
A dangling pointer is something which does not point to a valid
location any more.
#include <stdio.h>
int main()
{
int *iptr;
iptr = malloc(4);
free(iptr);
*iptr = 100;
return 0;
}
Example
#include <stdio.h>
int *foo(void)
{
int num = 5;
return &num_ptr;
}
int main()
{
int *iptr;
iptr = foo();
return 0;
}
Example

Embedded C
Pointers – Pitfalls – Wild Pointer
●
An uninitialized pointer pointing to a invalid location can be
called as an wild pointer.
#include <stdio.h>
int main()
{
int *iptr_1; /* Wild Pointer */
static int *iptr_2; / Not a wild pointer */
return 0;
}
Example

Embedded C
Pointers – Pitfall - Memory Leak
●
Improper usage of the memory allocation will lead to
memory leaks
●
Failing to deallocating memory which is no longer needed
is one of most common issue.
●
Can exhaust available system memory as an application
runs longer.

Embedded C
Pointers – Pitfall - Memory Leak
#include <stdio.h>
int main()
{
int *num_array, sum = 0, no_of_elements, i;
while (1)
{
printf(“Enter the number of elements: n”);
scanf(“%d”, &no_of_elements);
num_array = malloc(no_of_elements);
sum = 0;
for (i = 0; i < no_of_elements; i++)
{
scanf(“%d”, &num_array[i]);
sum += num_array[i];
}
printf(“The sum of array elements are %dn”, sum);
/* Forgot to free!! */
}
return 0;
}
Example

Embedded C
Pointers – Pitfalls – Bus Error
●
A bus error is a fault raised by hardware, notifying an
operating system (OS) that, a process is trying to access
memory that the CPU cannot physically address: an invalid
address for the address bus, hence the name.
#include <stdio.h>
int main()
{
char array[sizeof(int) + 1];
int *ptr1, *ptr2;
ptr1 = &array[0];
ptr2 = &array[1];
scanf(“%d %d”, ptr1, ptr2);
return 0;
}
Example

Embedded C
Pointers – Const Qualifier
#include <stdio.h>
int main()
{
int const *num = NULL;
return 0;
}
Example
The location, its pointing to is
constant
#include <stdio.h>
int main()
{
int * const num = NULL;
return 0;
}
Example
The pointer is constant

Embedded C
Pointers – Multilevel
●
A pointer, pointing to another pointer which can be pointing
to others pointers and so on is know as multilevel pointers.
●
We can have any level of pointers.
●
As the depth of the level increase we have to bit careful while
dealing with it.

Embedded C
#include <stdio.h>
int main()
{
int num = 10;
int *ptr1 = &num;
int **ptr2 = &ptr1;
int ***ptr3 = &ptr2;
printf(“%d”, ptr3);
printf(“%d”, *ptr3);
printf(“%d”, **ptr3);
printf(“%d”, ***ptr3);
return 0;
}
Example
101000
num

Embedded C
#include <stdio.h>
int main()
{
int num = 10;
int *ptr1 = &num;
int **ptr2 = &ptr1;
return 0;
}
Example
101000
num
10002000
ptr1

Embedded C
#include <stdio.h>
int main()
{
int num = 10;
int *ptr1 = &num;
int **ptr2 = &ptr1;
return 0;
}
Example
101000
num
20003000
ptr2
10002000
ptr1

Embedded C
#include <stdio.h>
int main()
{
int num = 10;
int *ptr1 = &num;
int **ptr2 = &ptr1;
return 0;
}
Example
101000
num
30004000
ptr3
20003000
ptr2
10002000
ptr1

Embedded C
#include <stdio.h>
int main()
{
int num = 10;
int *ptr1 = &num;
int **ptr2 = &ptr1;
return 0;
}
Example
101000
num
30004000
ptr3
20003000
ptr2
10002000
ptr1
Output 3000→

Embedded C
#include <stdio.h>
int main()
{
int num = 10;
int *ptr1 = &num;
int **ptr2 = &ptr1;
return 0;
}
Example
101000
num
30004000
ptr3
20003000
ptr2
10002000
ptr1
Output 2000→

Embedded C
#include <stdio.h>
int main()
{
int num = 10;
int *ptr1 = &num;
int **ptr2 = &ptr1;
return 0;
}
Example
101000
num
30004000
ptr3
20003000
ptr2
10002000
ptr1
Output 1000→

Embedded C
#include <stdio.h>
int main()
{
int num = 10;
int *ptr1 = &num;
int **ptr2 = &ptr1;
return 0;
}
Example
101000
num
30004000
ptr3
20003000
ptr2
10002000
ptr1
Output 10→

Embedded C
Pointers – 2D Array
ROW
S
COLUMS

Embedded C
ROWS
COLS
1 1
2 2
1
2
R0
R1
C0 C2
00 02
10 12
C1
01
11

Embedded C
#include <stdio.h>
int main()
{
int a[2][3] = {1, 2, 3, 4, 5, 6};
return 0;
}
Example
Total Memory: ROWS * COLS * sizeof(datatype) Bytes

Embedded C
Pointers – 2D Array - Referencing
41012
a
31008
21004
11000
[1] [0]
[0] [2]
[0] [1]
[0] [0]
2 * 1D array linearly
placed in memory
Index to access the
1D array
51016 [1] [1]
61020 [1] [2]
2nd
1D Array with base address 1012
a[1] = &a[1][0] = a + 1 1012→
1st
1D Array with base address 1000
a[0] = &a[0][0] = a + 0 1000→
a

Embedded C
Pointers – 2D Array - Dereferencing
41012
a
31008
21004
11000
[1] [0]
[0] [2]
[0] [1]
[0] [0]
2 * 1D array linearly
placed in memory
Index to access the
1D array
51016 [1] [1]
61020 [1] [2]
Example 1: Say a[0][1] is to be accessed, then
decomposition happens like,
a[0][1] = *(a[0] + 1 * sizeof(type))
A[0][1] = *(*(a + 0 * sizeof(1D array)) + 1 * sizeof(type))
A[0][1] = *(*(1000 + 0 * 12) + 1 * 4)
A[0][1] = *(*(1000 + 0) + 4)
A[0][1] = *(*(1004))
A[0][1] = 2
Example 2: Say a[1][2] is to be accessed, then
decomposition happens like,
a[1][2] = *(a[1] + 2 * sizeof(type))
A[0][1] = *(*(a + 1 * sizeof(1D array)) + 2 * sizeof(type))
A[0][1] = *(*(1000 + 1 * 12) + 2 * 4)
A[0][1] = *(*(1000 + 12) + 8)
A[0][1] = *(*(1020))
A[0][1] = 6
a

Embedded C
Pointers – Array of pointers
datatype *ptr_name[SIZE]
Syntax
int a = 10;
int b = 20;
int c = 30;
int *ptr[3];
ptr[0] = &a;
ptr[1] = &b;
ptr[2] = &c;
Example
101000
a
202000
b
303000
c

Embedded C
Syntax
int a = 10;
int b = 20;
int c = 30;
int *ptr[3];
ptr[0] = &a;
ptr[1] = &b;
ptr[2] = &c;
Example
101000
a
202000
b
303000
c
? ? ?
4000 4004 4008
ptr

Embedded C
Syntax
int a = 10;
int b = 20;
int c = 30;
int *ptr[3];
ptr[0] = &a;
ptr[1] = &b;
ptr[2] = &c;
Example
101000
a
202000
b
303000
c
1000 2000 3000
4000 4004 4008
ptr

Embedded C
Syntax
int a[2] = {10, 20};
int b[2] = {30, 40};
int c[2] = {50, 60};
int *ptr[3];
ptr[0] = a;
ptr[1] = b;
ptr[2] = c;
Example
201004
a
402004
b
603004
c101000 302000 503000

Embedded C
Syntax
int a[2] = {10, 20};
int b[2] = {30, 40};
int c[2] = {50, 60};
int *ptr[3];
ptr[0] = a;
ptr[1] = b;
ptr[2] = c;
Example
? ? ?ptr
201004
a
402004
b
603004
c101000 302000 503000
4000 4004 4008

Embedded C
Syntax
int a[2] = {10, 20};
int b[2] = {30, 40};
int c[2] = {50, 60};
int *ptr[3];
ptr[0] = a;
ptr[1] = b;
ptr[2] = c;
Example
1000 2000 3000ptr
201004
a
402004
b
603004
c101000 302000 503000
4000 4004 4008

Embedded C
#include <stdio.h>
void print_array(int **p)
{
int i;
for (i = 0; i < 3; i++)
{
printf(“%d ”, *p[i]);
printf(“at %pn”, p[i]);
}
}
int main()
{
int a = 10;
int b = 20;
int c = 30;
int *ptr[3] = {&a, &b, &c};
print_array(ptr);
return 0;
}
Example
10a 20
2000
b 30
3000
c
1000

Embedded C
#include <stdio.h>
{
int i;
for (i = 0; i < 3; i++)
{
}
}
int main()
{
int a = 10;
int b = 20;
int c = 30;
int *ptr[3] = {&a, &b, &c};
print_array(ptr);
return 0;
}
Example
10a 20
2000
b 30
3000
c
1000 2000 3000
4000 4004 4008
ptr
1000

Embedded C
#include <stdio.h>
{
int i;
for (i = 0; i < 3; i++)
{
}
}
int main()
{
int a = 10;
int b = 20;
int c = 30;
int *ptr[3] = {&a, &b, &c};
print_array(ptr);
return 0;
}
Example
10a 20
2000
b 30
3000
c
1000 2000 3000
4000 4004 4008
ptr
4000p
5000
1000

Embedded C
S_____s – Fill in the blanks please ;)
`

Embedded C
Strings
`
A set of things tied or threaded together on a thin cord.
Source: Google
String of Beads
Bead
String
Start of String
String ends hereContains n numbers of Beads

Embedded C
Strings
●
Contiguous sequence of characters
●
Easily stores ASCII and its extensions
●
End of the string is marked with a special character, the
null character '0'
●
'0' is implicit in strings enclosed with “”
●
Example
“You know, now this is what a string is!”

Embedded C
Strings - Initializations
Examples
char char_array[5] = {'H', 'E', 'L', 'L', 'O'}; Character Array
char str[6] = {'H', 'E', 'L', 'L', 'O', '0'}; String
char str[6] = {“H”, “E”, “L”, “L”, “O”}; Invalid
char str[6] = {“H” “E” “L” “L” “O”}; Valid
char str[] = {'H', 'E', 'L', 'L', 'O', '0'}; Valid
char str[6] = {“HELLO”}; Valid
char str[6] = “HELLO”; Valid
char str[] = “HELLO”; Valid
char *str = “HELLO”; Valid

Embedded C
Strings - Size
Examples
#include <stdio.h>
int main()
{
char char_array_1[5] = {'H', 'E', 'L', 'L', 'O'};
char char_array_2[] = “Hello”;
sizeof(char_array_1);
sizeof(char_array_2);
return 0;
}
The size of the array
Is calculated So,
5, 6
int main()
{
char *str = “Hello”;
sizeof(str);
return 0;
}
The size of pointer is
always constant so,
4 (32 Bit Sys)

Embedded C
Strings - Size
Example
#include <stdio.h>
int main()
{
if (sizeof(“Hello” “World”) == sizeof(“Hello”) + sizeof(“World”))
{
printf(“WoWn”);
}
else
{
printf(“HuHn”);
}
return 0;
}

Embedded C
Strings - Manipulations
Examples
char str1[6] = “Hello”;
char str2[6];
str2 = “World”;
Not possible to assign a string to a
array since its a constant pointer
char *str3 = “Hello”;
char *str4;
str4 = “World”;
Possible to assign a string to
a pointer since its variable
str1[0] = 'h'; Valid. str1 contains “hello”
str3[0] = 'w'; Invalid. str3 might be stored in read only section.
Undefined behaviour

Embedded C
Strings - Sharing
Example
#include <stdio.h>
int main()
{
if (str1 == str2)
{
printf(“Hoo. They share same spacen”);
}
else
{
printf(“No. They are in different spacen”);
}
return 0;
}

Embedded C
Strings – Library Functions
Puropse Prototype Return Values
Length size_t strlen(const char *str) String Length
Compare int strcmp(const char *str1, const char *str2) str1 < str2 < 0→
str1 > str2 > 0→
str1 = str2 = 0→
Copy char *strcpy(char *dest, const char *src) Pointer to dest
Check
String
char *strstr(const char *haystack, const char *needle) Pointer to the
beginning of
substring
Check
Character
char *strchr(const char *s, int c) Pointer to the
matched char
else NULL
Merge char *strcat(char *dest, const char *src) Pointer to dest

Embedded C
Memory Segments
Linux OS
P1
User
Space
Kernel
Space
The Linux OS is divided into two major sections
●
User Space
●
Kernel Space
The user programs cannot access the kernel
space. If done will lead to segmentation
violation
Let us concentrate on the user space section
here

Embedded C
Memory Segments
Linux OS
P1
User
Space
Kernel
Space
P1
P2
P3
.
.
.
P1
Pn-1
Pn
User Space
The User space contains
many processes
Every process will be
scheduled by the kernel
Each process will have its
memory layout discussed
in next slide

Embedded C
Memory Segments
Stack
Text Segment
Initialized
Heap
.BSS
(Uninitialized)
Command Line
Arguments
Hole
Data
Segment
Memory Segments
P1
P2
P3
.
.
.
P1
Pn-1
Pn
User Space
The memory segment of a
program contains four
major areas.
●
Text Segment
●
Stack
●
Data Segment
●
Heap

Embedded C
Memory Segments – Text Segment
Stack
Text Segment
Initialized
Heap
.BSS
(Uninitialized)
Command Line
Arguments
Hole
Data
Segment
Memory Segments
Also referred as Code Segment
Holds one of the section of program in
object file or memory
In memory, this is place below the heap or
stack to prevent getting over written
Is a read only section and size is fixed

Embedded C
Memory Segments – Data Segment
Stack
Text Segment
Initialized
Heap
.BSS
(Uninitialized)
Command Line
Arguments
Hole
Data
Segment
Memory Segments
Contains 2 sections as initialized and
uninitialized data segments
Initialized section is generally called as Data
Segment
Uninitialized section is referred as BSS
(Block Started by Symbol) usually filled
with 0s

Embedded C
Memory Segments – Data Segment
Stack
Text Segment
Initialized
Heap
.BSS
(Uninitialized)
Command Line
Arguments
Hole
Data
Segment
Memory Segments
Dynamic memory allocation takes place here
Begins at the end of BSS and grows
upward from there

Embedded C
Memory Segments – Stack Segment
Stack
Text Segment
Initialized
Heap
.BSS
(Uninitialized)
Command Line
Arguments
Hole
Data
Segment
Memory Segments
Adjoins the heap area and grow in opposite
area of heap when stack and heap pointer
meet (Memory Exhausted)
Typically loaded at the higher part of memory
A “stack pointer” register tracks the top
of the stack; it is adjusted each time
a value is “pushed” onto the stack
Typically loaded at the higher part of memoryTypically loaded at the higher part of
memory
The set of values pushed for one function
call is termed a “stack frame”

Embedded C
Memory Segments – Stack Segment
Stack
Text Segment
Initialized
Heap
.BSS
(Uninitialized)
Command Line
Arguments
Hole
Data
Segment
Local Variables
Return Address
Parameter List
Memory Segments Stack Frame
A stack frame contain at least
of a return address

Embedded C
Memory Segments – Stack Frame
#include <stdio.h>
int main()
{
int num1 = 10, num2 = 20;
int sum = 0;
return 0;
}
int add_numbers(int n1, int n2)
{
int s = 0;
s = n1 + n2;
return s;
}
num1 = 10
num2 = 20
sum = 0
Return Address to the caller
Stack Frame
main()
s = 0
add_numbers()Return Address to the main()
n1 = 10
n2 = 20

Embedded C
Memory Segments - Runtime
●
Run-time memory includes four (or more) segments
– Text area: program text
– Global data area: global & static variables
– Allocated during whole run-time
●
Stack: local variables & parameters
– A stack entry for a functions
– Allocated (pushed) - When entering a function
– De-allocated (popped) - When the function returns
●
Heap
– Dynamic memory
– Allocated by malloc()
– De-allocated by free()

Embedded C
Storage Classes
Storage Class Scope Lifetime Memory
Allocation
auto Within the block /
Function
Till the end of the block /
function
Stack
register Within the block /
Function
Till the end of the block /
function
Register
static local Within the block /
Function
Till the end of the program Data Segment
static global File Till the end of the program Data segment
extern Program Till the end of the program Data segment

Embedded C
Storage Classes
Variable Storage Class Memory Allocation
global_1 No .BSS
global_2 No Initialized data segment
global_3 Static global .BSS
global_4 Static global Initialized data segment
local_1 auto stack
local_2 Static local .BSS
local_3 Static local Initialized data segment
iter Register Registers
#include <stdio.h>
int globa1_1;
int globa1_2 = 10;
static int globa1_3;
static int globa1_4 = 10;
int main()
{
int local_1;
static int local_1;
static int local_2 = 20;
register int i;
for (i = 0; i < 0; i++)
{
/* Do Something */
}
return 0;
}
Example

Embedded C
Declaration
extern int num1;
extern int num1;
int main();
int main()
{
int num1, num2;
char short_opt;
...
}
Declaration specifies type to the
variables
Its like an announcement and hence
can be made 1 or more times
Declaration about num1
Declaration about main function
Declaration about num1 yet again!!

Embedded C
Storage Classes - extern
#include <stdio.h>
int num;
int main()
{
while (1)
{
num++;
func_1();
sleep(1);
func_2();
}
return 0;
}
file1.c
#include <stdio.h>
extern int num;
int func_1()
{
printf(“num is %d from file2n”, num);
return 0;
}
file2.c
file3.c
#include <stdio.h>
extern int num;
int func_2()
{
printf(“num is %d from file3n”, num);
return 0;
}

Embedded C
Preprocessor
●
One of the step performed before compilation
●
Is a text substitution tool and it instructs the compiler to
do required pre-processing before the actual compilation
●
Instructions given to preprocessor are called
preprocessor directives and they begin with “#” symbol
●
Few advantages of using preprocessor directives would
be,
– Easy Development
– Readability
– Portability

Embedded C
Preprocessor – Compilation Stages
●
Before we proceed with preprocessor directive let's try to
understand the stages involved in compilation
●
Some major steps involved in compilation are
– Pre-processing
– Compilation
– Assembly
– Linking
●
The next slide provide the flow of these stages

Embedded C
Preprocessor – Compilation Stages
Source Code
Expanded Source
Code
Assembly Source
Code
Object Code
Executable
.cPreprocessor
Compiler
Assembler
Linker
Loader
.i
.s
.o
.out
gcc -E file.c
gcc -S file.c
gcc -c file.c
gcc -save-temps file.c would generate all intermediate files

Embedded C
Preprocessor – Directives
#include
#define
#undef
#ifdef
#ifndef
#else
#endif
#if
#else
#elif
#error
#warning
#line
#pragma
#
##

Embedded C
Preprocessor – Header Files
●
A header file is a file containing C declarations and macro
definitions to be shared between several source files.
●
Has to be included using C preprocessing directive
‘#include'
●
Header files serve two purposes.
– Declare the interfaces to parts of the operating system by
supplying the definitions and declarations you need to
invoke system calls and libraries.
– Your own header files contain declarations for interfaces
between the source files of your program.

Embedded C
Preprocessor – Header Files vs Source Files
.h .cVS
●
Declarations
●
Sharable/reusable
●
#defines
●
Datatypes
●
Used by more than 1
file
●
Function and variable
definitions
●
Non sharable/reusable
●
#defines
●
Datatypes

Embedded C
Preprocessor – Header Files - Syntax
Syntax
#include <file.h> ●
System header files
●
It searches for a file named file
in a standard list of system
directories
Syntax
#include “file.h” ●
Local (your) header files
●
It searches for a file named file
first in the directory containing the
current file, then in the quote
directories and then the same
directories used for <file>

Embedded C
Preprocessor – Header Files - Operation
int num;
#include “file2.h”
int main()
{
puts(test());
return 0;
}
file1.c
char *test(void);
file2.hfile2.c
char *test(void)
{
static char *str = “Hello”;
return str;
}
int num;
char *test(void);
int main()
{
puts(test());
return 0;
}

Embedded C
Preprocessor – Header Files – Search Path
●
On a normal Unix system GCC by default will look for
headers requested with #include <file> in:
– /usr/local/include
– libdir/gcc/target/version/include
– /usr/target/include
– /usr/include
●
You can add to this list with the -I <dir> command-line
option
`gcc -print-prog-name=cc1` -v would the search path info

Embedded C
Preprocessor – Header Files – Once-Only
●
If a header file happens to be included twice, the compiler
will process its contents twice causing an error
●
E.g. when the compiler sees the same structure definition
twice
●
This can be avoided like
#ifndef NAME
#define NAME
/* The entire file is protected */
#endif
Example

Embedded C
Preprocessor – Macro – Object-Like
●
An object-like macro is a simple identifier which will be
replaced by a code fragment
●
It is called object-like because it looks like a data object
in code that uses it.
●
They are most commonly used to give symbolic names to
numeric constants
#define SYMBOLIC_NAME CONSTANTS
Syntax
#define BUFFER_SIZE 1024
Example

Embedded C
Preprocessor – Macro – Arguments
●
Function-like macros can take arguments, just like true
functions
●
To define a macro that uses arguments, you insert
parameters between the pair of parentheses in the macro
definition that make the macro function-like
Example
#include <stdio.h>
#define SET_BIT(num, pos) (num | (1 << pos))
int main()
{
SET_BIT(0, 2);
return 0;
}

Embedded C
Preprocessor – Macro – Multiple Lines
●
You may continue the
definition onto multiple
lines, if necessary,
using backslash-
newline.
●
When the macro is
expanded, however, it
will all come out on one
line
Example
#include <stdio.h>
#define SWAP(a, b)
{
int temp = a;
a = b;
b = temp;
}
int main()
{
int num1 = 10, num2= 20;
SWAP(num1, num2);
printf(“%d %dn”, num1, num2);
return 0;
}

Embedded C
Preprocessor – Macro – Stringification
#include <stdio.h>
#define WARN_IF(EXP)
do
{
x--;
if (EXP)
{
fprintf(stderr, "Warning: " #EXP "n");
}
} while (x);
int main()
{
int x = 5;
WARN_IF(x == 0);
return 0;
}
●
You can convert a macro
argument into a string
constant by adding #
Example

Embedded C
Preprocessor – Macro – Concatenation
#include <stdio.h>
#define CAT(x) (x##_val)
int main()
{
int int_val = 4;
float float_val = 2.54;
printf("int val = %dn", CAT(int));
printf("float val = %fn", CAT(float));
return 0;
}
Example

Embedded C
Preprocessor – Macro – Standard Predefined
●
Several object-like macros are predefined; you use them
without supplying their definitions.
●
Standard are specified by the relevant language
standards, so they are available with all compilers that
implement those standards
Example
#include <stdio.h>
int main()
{
printf(“Program: “%s” ”, __FILE__);
printf(“was compiled on %s at %s. ”, __DATE__, __TIME__);
printf(“This print is from Function: ”%s” at line %dn”, __func__, __LINE__);
return 0;
}

Embedded C
Preprocessor – Conditional Compilation
●
A conditional is a directive that instructs the
preprocessor to select whether or not to include a chunk
of code in the final token stream passed to the compiler
●
Preprocessor conditionals can test arithmetic
expressions, or whether a name is defined as a macro, or
both simultaneously using the special defined operator
●
A conditional in the C preprocessor resembles in some
ways an if statement in C with the only difference being
it happens in compile time
●
Its purpose is to allow different code to be included in
the program depending on the situation at the time of
compilation.

Embedded C
Preprocessor – Conditional Compilation
●
There are three general reasons to use a conditional.
– A program may need to use different code depending
on the machine or operating system it is to run on
– You may want to be able to compile the same source
file into two different programs, like one for debug
and other as final
– A conditional whose condition is always false is one
way to exclude code from the program but keep it as a
sort of comment for future reference

Embedded C
Preprocessor – Conditional Compilation - ifdef
#ifdef MACRO
/* Controlled Text */
#endif
Syntax

Embedded C
Preprocessor – Conditional Compilation - defined
#if defined (ERROR) && (WARNING)
#endif
Syntax

Embedded C
Preprocessor – Conditional Compilation - if
#if expression
#endif
Syntax

Embedded C
Preprocessor – Conditional Compilation - else
#if expression
/* Controlled Text if true */
#else
/* Controlled Text if false */
#endif
Syntax

Embedded C
Preprocessor – Conditional Compilation - elif
#if DEBUG_LEVEL == 1
/* Controlled Text*/
#elif DEBUG_LEVEL == 2
#else
#endif
Syntax

Embedded C
Preprocessor – Conditional Com... – Deleted Code
#if 0
/* Deleted code while compiling */
/* Can be used for nested code comments */
/* Avoid for general comments */
#endif
Syntax

Embedded C
Preprocessor – Diagnostic
●
The directive ‘#error’ causes the preprocessor to report a
fatal error. The tokens forming the rest of the line
following ‘#error’ are used as the error message
●
The directive ‘#warning’ is like ‘#error’, but causes the
preprocessor to issue a warning and continue
preprocessing. The tokens following ‘#warning’ are used
as the warning message

Embedded C
User Defined Datatypes (UDT)
●
Sometimes it becomes tough to build a whole software that
works only with integers, floating values, and characters.
●
In circumstances such as these, you can create your own
data types which are based on the standard ones
●
There are some mechanisms for doing this in C:
– Structures
– Unions
– Typedef
– Enums
●
Hoo!!, let's not forget our old friend _r_a_ which is a user
defined data type too!!.

Embedded C
UDTs - Structures
●
A complex data type declaration that defines a physically
grouped list of variables to be placed under one name in a
block of memory
●
Unlike arrays, structures allows different data types in the
allocated memory region
●
Generally useful whenever a lot of data needs to be
grouped together
●
Allows us to have OOPS concepts in C,
– Data first
– Data centric (Manipulations on data)
– Better Design

Embedded C
UDTs - Structures
struct StructureName
{
/* Group of data types */
};
Syntax
●
So we if create a structure for the above requirement, it
would look like,
struct Student
{
int id;
char name[30];
char address[150]
};
Example
●
If we consider the Student as
an example, The admin
should have at least some
important data like name, ID
and address.

Embedded C
UDTs – Structures – Declartion and definition
struct Student
{
int id;
char name[30];
char address[150];
};
int main()
{
struct Student s1;
return 0;
}
Example
●
Name of the datatype. Note it's
struct Student and not Student
●
Are called as fields or members of
of the structure
●
Declaration ends here
●
The memory is not yet allocated!!
●
s1 is a variable of type
struct Student
●
The memory is allocated now

Embedded C
UDTs – Structures – Memory Layout
struct Student
{
int id;
char name[30];
char address[150];
};
int main()
{
struct Student s1;
return 0;
}
Example ●
What does s1 contain?
●
How can we draw it's memory
layout?
?
s1
id
? name
? address

Embedded C
UDTs – Structures - Access
struct Student
{
int id;
char name[30];
char address[150];
};
int main()
{
struct Student s1;
s1.id = 10;
return 0;
}
Example ●
How to write into id now?
●
It's by using “.” (Dot)
operator
10
s1
id
? name
? address
●
Now please assign the name for s1

Embedded C
UDTs – Structures - Initialization
struct Student
{
int id;
char name[30];
char address[150];
};
int main()
{
struct Student s1 = {10, “Tingu”, “Bangalore”};
return 0;
}
Example
10
s1
id
“Tingu” name
“Bangalore” address

Embedded C
UDTs – Structures - Copy
struct Student
{
int id;
char name[30];
char address[150];
};
int main()
{
struct Student s2;
s2 = s1;
return 0;
}
Example
10
s2
id
“Tingu” name
“Bangalore” address
Structure name does not represent its address. (No correlation with arrays)

Embedded C
UDTs – Structures - Address
struct Student
{
int id;
char name[30];
char address[150];
};
int main()
{
printf(“Structure starts at %pn”, &s1);
printf(“Member id is at %pn”, &s1.id);
printf(“Member name is at %pn”, &s1.name);
printf(“Member address is at %pn”, &s1.address);
return 0;
}
Example

Embedded C
UDTs – Structures - Pointers
●
Pointers!!!. Not again ;). Fine don't worry, not a big deal
●
But do you have any idea how to create it?
●
Will it be different from defining them like in other data
types?

Embedded C
UDTs – Structures - Pointer
struct Student
{
int id;
char name[30];
char address[150];
};
int main()
{
struct Student s1;
struct Student *sptr = &s1;
return 0;
}
Example
?
s1
id
? name
? address
1000
sptr
1000
2000

Embedded C
UDTs – Structures – Pointer - Access
struct Student
{
int id;
char name[30];
char address[150];
};
int main()
{
struct Student s1;
(*sptr).id = 10;
return 0;
}
Example
10
s1
id
? name
? address
1000
sptr
1000
2000

Embedded C
UDTs – Structures – Pointer – Access – Arrow
struct Student
{
int id;
char name[30];
char address[150];
};
int main()
{
struct Student s1;
sptr->id = 10;
return 0;
}
Example
10
s1
id
? name
? address
1000
sptr
1000
2000
Note: we can access the structure pointer as seen
in the previous slide. The Arrow operator is just
convenience and frequently used

Embedded C
UDTs – Structures - Functions
●
The structures can be passed as parameter and can be
returned from a function
●
This happens just like normal datatypes.
●
The parameter passing can have two methods again as
normal
– Pass by value
– Pass by reference

Embedded C
UDTs – Structures – Functions – Pass by Value
struct Student
{
int id;
char name[30];
char address[150];
};
void data(struct Student s)
{
s.id = 10;
}
int main()
{
struct Student s1;
data(s1);
return 0;
}
Example
Not recommended on
larger structures

Embedded C
UDTs – Structures – Functions – Pass by Reference
struct Student
{
int id;
char name[30];
char address[150]
};
void data(struct Student *s)
{
s->id = 10;
}
int main()
{
struct Student s1;
data(&s1);
return 0;
}
Example
Recommended on
larger structures

Embedded C
UDTs – Structures – Functions – Return
struct Student
{
int id;
char name[30];
char address[150]
};
struct Student data(struct Student s)
{
s.id = 10;
return s;
}
int main()
{
struct Student s1;
s1 = data(s1);
return 0;
}
Example

Embedded C
UDTs – Structures – Padding
●
Adding of few extra useless bytes (in fact skip address) in
between the address of the members are called
structure padding.
●
What!!?, wasting extra bytes!!, Why?
●
This is done for Data Alignment.
●
Now!, what is data alignment and why did this issue
suddenly arise?
●
No its is not sudden, it is something the compiler would
internally while allocating memory.
●
So let's understand data alignment in next few slides

Embedded C
Data Alignment
●
A way the data is arranged and accessed in computer
memory.
●
When a modern computer reads from or writes to a
memory address, it will do this in word sized chunks (4
bytes in 32 bit system) or larger.
●
The main idea is to increase the efficiency of the CPU,
while handling the data, by arranging at a memory
address equal to some multiple of the word size
●
So, Data alignment is an important issue for all
programmers who directly use memory.

Embedded C
Data Alignment
●
If you don't understand data and its address alignment
issues in your software, the following scenarios, in
increasing order of severity, are all possible:
– Your software will run slower.
– Your application will lock up.
– Your operating system will crash.
– Your software will silently fail, yielding incorrect results.

Embedded C
Data Alignment
int main()
{
char ch = 'A';
int num = 0x12345678;
}
Example ●
Lets consider the code as
given
●
The memory allocation we
expect would be like shown
in figure
●
So lets see how the CPU tries
to access these data in next
slides
'A'
78
56
34
12
?
?
?
0
1
2
3
4
5
6
7

Embedded C
Data Alignment
int main()
{
char ch = 'A';
int num = 0x12345678;
}
Example ●
Fetching the character by
the CPU will be like shown
below
41
78
56
34
12
?
?
?
0
1
2
3
4
5
6
7
0 4 Bytes
41
78
56
34
41
0
0
0

Embedded C
Data Alignment
int main()
{
char ch = 'A';
int num = 0x12345678;
}
Example ●
Fetching the integer by
below
41
78
56
34
12
?
?
?
0
1
2
3
4
5
6
7
0 4 Bytes
41
78
56
34

Embedded C
Data Alignment
int main()
{
char ch = 'A';
int num = 0x12345678;
}
Example ●
below
41
78
56
34
12
?
?
?
0
1
2
3
4
5
6
7
4 4 Bytes
41
78
56
34
12
?
?
?

Embedded C
Data Alignment
int main()
{
char ch = 'A';
int num = 0x12345678;
}
Example ●
below
41
78
56
34
12
?
?
?
0
1
2
3
4
5
6
7
41
78
56
34
12
?
?
?
78
56
34
0
Shift 1 Byte Up
0
0
0
12
78
56
34
12
Shift 3 Byte Down
Combine

Embedded C
UDTs – Structures – Data Alignment - Padding
●
Because of the data alignment issue, structures uses padding
between its members if the don't fall under even address.
●
So if we consider the following structure the memory
allocation will be like shown in below figure
struct Test
{
char ch1;
int num;
char ch2;
}
Example
ch1
pad
pad
pad
num
num
num
num
0
1
2
3
4
5
6
7
ch2
pad
pad
pad
8
9
A
B

Embedded C
UDTs – Structures – Data Alignment - Padding
●
You can instruct the compiler to modify the default padding
behavior using #pragma pack directive
#pragma pack(1)
struct Test
{
char ch1;
int num;
char ch2;
}
Example
ch1
num
num
num
num
ch2
0
1
2
3
4
5

Embedded C
UDTs – Structures – Bit Fields
●
The compiler generally gives the memory allocation in
multiples of bytes, like 1, 2, 4 etc.,
●
What if we want to have freedom of having getting
allocations in bits?!.
●
This can be achieved with bit fields.
●
But note that
– The minimum memory allocation for a bit field member
would be a byte that can be broken in max of 8 bits
– The maximum number of bits assigned to a member would
depend on the length modifier
– The default size is equal to word size

Embedded C
struct Nibble
{
unsigned char lower : 4;
unsigned char upper : 4;
};
Example
●
The above structure divides a char into two nibbles
●
We can access these nibbles independently

Embedded C
struct Nibble
{
};
int main()
{
struct Nibble nibble;
nibble.upper = 0xA;
nibble.lower = 0x2;
return 0;
}
Example
?1000
nibble
? ? ? ? ? ? ? ?

Embedded C
struct Nibble
{
};
int main()
{
nibble.upper = 0xA;
nibble.lower = 0x2;
return 0;
}
Example
0xA?1000
nibble
1 0 1 0 ? ? ? ?

Embedded C
struct Nibble
{
};
int main()
{
nibble.upper = 0xA;
nibble.lower = 0x2;
return 0;
}
Example
0xA21000
nibble
1 0 1 0 0 0 1 0

Embedded C
UDTs – Unions
●
Like structures, unions may have different members with
different data types.
●
The major difference is, the structure members get
different memory allocation, and in case of unions there
will be single memory allocation for the biggest data type

Embedded C
UDTs – Unions
union Test
{
char option;
int id;
double height;
};
Example
●
The above union will get the size allocated for the type
double
●
The size of the union will be 8 bytes.
●
All members will be using the same space when accessed
●
The value the union contain would be the latest update
●
So as summary a single variable can store different type of
data as required

Embedded C
UDTs – Unions
union Test
{
char option;
int id;
double height;
};
int main()
{
union Test temp_var;
temp_var.height = 7.2;
temp_var.id = 0x1234;
temp_var.option = '1';
return 0;
}
Example
?
?
?
?
1000 ?
?
?
?
1007
Total 8 Bytes
allocated
since longest
member is
double
temp_var

Embedded C
UDTs – Unions
0xCC
0xCC
0x1C
0x40
1000 0xCD
0xCC
0xCC
0xCC
1007
double uses
its memory
union Test
{
char option;
int id;
double height;
};
int main()
{
return 0;
}
Example
temp_var

Embedded C
UDTs – Unions
0xCC
0xCC
0x1C
0x40
1000 0x34
0x12
0x00
0x00
1007
int shares
double's
memory
union Test
{
char option;
int id;
double height;
};
int main()
{
return 0;
}
Example
temp_var

Embedded C
UDTs – Unions
0xCC
0xCC
0x1C
0x40
1000 0x31
0x12
0x00
0x00
1007
char shares
double's
memory
union Test
{
char option;
int id;
double height;
};
int main()
{
return 0;
}
Example
temp_var

Embedded C
UDTs - Typedefs
●
Typedef is used to create a new name to the existing
types.
●
K&R states that there are two reasons for using a
typedef.
– First, it provides a means to make a program more
portable. Instead of having to change a type everywhere it
appears throughout the program's source files, only a single
typedef statement needs to be changed.
– Second, a typedef can make a complex definition or
declaration easier to understand.

Embedded C
UDTs - Typedefs
typedef unsigned int uint;
int main()
{
uint number;
return 0;
}
Example
typedef int * intptr;
int main()
{
intptr ptr1, ptr2, ptr3;
return 0;
}
Example
typedef struct _Student
{
int id;
char name[30];
char address[150]
} Student;
void data(Student s)
{
s.id = 10;
}
int main()
{
Student s1;
data(s1);
return 0;
}
Example

Embedded C
UDTs - Typedefs
#include <stdio.h>
typedef int (*fptr)(int, int);
int add(int num1, int num2)
{
return num1 + num2;
}
int main()
{
fptr function;
function = add;
printf(“%dn”, function(2, 4));
return 0;
}
Example

Embedded C
UDTs – Enums
●
Set of named integral values
enum Boolean
{
e_false,
e_true
};
Examples ●
The above example has two members
with its values starting from 0. i.e,
e_false = 0 and e_true = 1.
●
The member values can be explicitly
initialized
●
There is no constraint in values, it can be
in any order and same values can be
repeated
●
Enums does not have name space of its
own, so we cannot have same name used
again in the same scope.
typedef enum
{
e_red = 1,
e_blue = 4,
e_green
} Color;
typedef enum
{
red,
blue
} Color;
int blue;

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Embedded C - Day 2

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