![REFERENCING AND DEREFERENCING OF
FUNCTION POINTER IN C
• Suppose we want to create a sorting function. It makes more sense to allow
the function’s caller to decide the order in which values are sorted (ascending,
descending, etc).
• One way is to provide a flag in the function argument to decide what to do,
but this is not flexible.
• Another way is to provide user flexibility to pass a function in our sort
function. This function can take two values as input and perform a
comparison between them. A syntax for our new function will look like.
void sort(int array[], int n, function comparison);](https://image.slidesharecdn.com/c-programmingfunctionpointers-220819084506-317d2bed/85/C-Programming-Function-pointers-pptx-10-320.jpg)
C-Programming Function pointers.pptx
- 2. INTRODUCTION • Function pointers are pointers that point to functions instead of data types. • They can be used to allow variability in the function that is to be called, at run-time. Syntax: •returnType (*name)(parameters) •typedef returntype (*name)(parameters) •typedef returnType Name(parameters); Name *name; •typedef returnType Name(parameters); typedef Name *NamePtr;
- 3. DECLARING A FUNCTION POINTER IN C Now that we know that functions have a unique memory address, we can use Function pointers in C that can point to the first executable code inside a function body. SYNTAX OF FUNCTION POINTER IN C return_type (* pointer_name) (datatype_arg_1, datatype_arg_1, ...);
- 4. • Declaring a function pointer in C is comparable to declaring a function except that when a function pointer is declared, we prefix its name which is an Asterisk * symbol. • For example, if a function has the declaration float foo (int, int); • Declaration Of a function pointer in C for the function foo will be // function pointer declaration float (*foo_pointer) (int, int); /* assigning the address of the function (foo) to function pointer */ foo_pointer = foo;
- 5. CALLING A FUNCTION THROUGH A FUNCTION POINTER IN C • Calling a function using a pointer is similar to calling a function in the usual way using the name of the function. • Suppose we declare a Function and its pointer as given below int (*pointer) (int); // function pointer declaration int areaSquare (int); // function declaration pointer = areaSquare;
- 6. To call the function areaSquare, we can create a function call using any of the three ways int length = 5; // Different ways to call the function // 1. using function name int area = areaSquare(length); // 2. using function pointer (a) int area = (*pointer)(length); // 3. using function pointer (b) int area = pointer(length); •The effect of calling functions using pointers or using their name is the same.
- 7. FUNCTIONS USING POINTER VARIABLES • C allows pointers to be passed in as function arguments and also return pointers from the function. • To pass pointers in the function, we simply declare the function parameter as pointer type. • When functions have their pointer type arguments, the changes made on them inside the function persists even after program exists function scope because the changes are made on the actual address pointed by the pointer. • This approach to pass arguments to a function is called as pass by reference because as shown in the figure below reference of the variable is passed to the function instead of the value stored in the address.
- 8. SAFE WAYS TO RETURN A POINTER FROM A FUNCTION 1. Return variables are either created using the keyword static or created dynamically at run time because such variables exist in memory beyond the scope of the called function. 2. Use arguments that are passed by their reference because such functions exist in the calling function scope.
- 9. FUNCTIONS USING POINTER VARIABLES • C allows pointers to be passed in as function arguments and also return pointers from the function. • To pass pointers in the function, we simply declare the function parameter as pointer type. • When functions have their pointer type arguments, the changes made on them inside the function persists even after program exists function scope because the changes are made on the actual address pointed by the pointer. • This approach to pass arguments to a function is called as pass by reference because as shown in the figure below reference of the variable is passed to the function instead of the value stored in the address.
- 10. REFERENCING AND DEREFERENCING OF FUNCTION POINTER IN C • Suppose we want to create a sorting function. It makes more sense to allow the function’s caller to decide the order in which values are sorted (ascending, descending, etc). • One way is to provide a flag in the function argument to decide what to do, but this is not flexible. • Another way is to provide user flexibility to pass a function in our sort function. This function can take two values as input and perform a comparison between them. A syntax for our new function will look like. void sort(int array[], int n, function comparison);