![CSE 332: C++ program structure and development environment
A Very Simple C++ Program
#include <iostream> // precompiler directive
using namespace std; // compiler directive
// definition of function named “main”
int main (int, char *[])
{
cout << “hello, world!” << endl;
return 0;
}](https://image.slidesharecdn.com/cprograms-230603064111-e88c8c30/85/C-_programs-ppt-4-320.jpg)
![CSE 332: C++ program structure and development environment
What is int main (int, char*[]) { ... } ?
• Defines the main function of any C++ program
• Who calls main?
– The runtime environment, specifically a function often called
something like crt0 or crtexe
• What about the stuff in parentheses?
– A list of types of the input arguments to function main
– With the function name, makes up its signature
– Since this version of main ignores any inputs, we leave off
names of the input variables, and only give their types
• What about the stuff in braces?
– It’s the body of function main, its definition](https://image.slidesharecdn.com/cprograms-230603064111-e88c8c30/85/C-_programs-ppt-7-320.jpg)
![CSE 332: C++ program structure and development environment
A Slightly Bigger C++ Program
#include <iostream>
using namespace std;
int main (int argc, char * argv[])
{
for (int i = 0; i < argc; ++i)
{
cout << argv[i] << endl;
}
return 0;
}](https://image.slidesharecdn.com/cprograms-230603064111-e88c8c30/85/C-_programs-ppt-10-320.jpg)
![CSE 332: C++ program structure and development environment
int argc, char * argv[]
• A way to affect the program’s behavior
– Carry parameters with which program was called
– Passed as parameters to main from crt0
– Passed by value (we’ll discuss what that means)
• argc
– An integer with the number of parameters (>=1)
• argv
– An array of pointers to C-style character strings
– Its array-length is the value stored in argc
– The name of the program is kept in argv[0]](https://image.slidesharecdn.com/cprograms-230603064111-e88c8c30/85/C-_programs-ppt-11-320.jpg)
![CSE 332: C++ program structure and development environment
{cout << argv[i] << endl;}
• Body of the for loop
• I strongly prefer to use braces with for, if,
while, etc., even w/ single-statement body
– Avoids maintenance errors when
adding/modifying code
– Ensures semantics/indentation say same thing
• argv[i]
– An example of array indexing
– Specifies ith position from start of argv](https://image.slidesharecdn.com/cprograms-230603064111-e88c8c30/85/C-_programs-ppt-13-320.jpg)
C++_programs.ppt
- 1. CSE 332: C++ program structure and development environment C++ Program Structure (and tools) Today we’ll talk generally about C++ development (plus a few platform specifics) • We’ll develop, submit, and grade code in Windows • It’s also helpful to become familiar with Linux – E.g., on shell.cec.wustl.edu • For example, running code through two different compilers can catch a lot more “easy to make” errors
- 2. CSE 332: C++ program structure and development environment Writing a C++ Program C++ source files (ASCII text) .cpp Programmer (you) emacs editor C++ header files (ASCII text) .h 1 source file = 1 compilation unit Makefile (ASCII text) Also: .C .cxx .cc Also: .H .hxx .hpp readme (ASCII text) Eclipse Visual Studio
- 3. CSE 332: C++ program structure and development environment What Goes Into a C++ Program? • Declarations: data types, function signatures, classes – Allows the compiler to check for type safety, correct syntax – Usually kept in “header” (.h) files – Included as needed by other files (to keep compiler happy) class Simple { typedef unsigned int UINT32; public: Simple (int i); int usage (char * program_name); void print_i (); private: struct Point2D { int i_; double x_; }; double y_; }; • Definitions: static variable initialization, function implementation – The part that turns into an executable program – Usually kept in “source” (.cpp) files void Simple::print_i () { cout << “i_ is ” << i_ << endl; } • Directives: tell compiler (or precompiler) to do something – More on this later
- 4. CSE 332: C++ program structure and development environment A Very Simple C++ Program #include <iostream> // precompiler directive using namespace std; // compiler directive // definition of function named “main” int main (int, char *[]) { cout << “hello, world!” << endl; return 0; }
- 5. CSE 332: C++ program structure and development environment What is #include <iostream> ? • #include tells the precompiler to include a file • Usually, we include header files – Contain declarations of structs, classes, functions • Sometimes we include template definitions – Varies from compiler to compiler – Advanced topic we’ll cover later in the semester • <iostream> is the C++ label for a standard header file for input and output streams
- 6. CSE 332: C++ program structure and development environment What is using namespace std; ? • The using directive tells the compiler to include code from libraries that have separate namespaces – Similar idea to “packages” in other languages • C++ provides a namespace for its standard library – Called the “standard namespace” (written as std) – cout, cin, and cerr standard iostreams, and much more • Namespaces reduce collisions between symbols – Rely on the :: scoping operator to match symbols to them – If another library with namespace mylib defined cout we could say std::cout vs. mylib::cout • Can also apply using more selectively: – E.g., just using std::cout
- 7. CSE 332: C++ program structure and development environment What is int main (int, char*[]) { ... } ? • Defines the main function of any C++ program • Who calls main? – The runtime environment, specifically a function often called something like crt0 or crtexe • What about the stuff in parentheses? – A list of types of the input arguments to function main – With the function name, makes up its signature – Since this version of main ignores any inputs, we leave off names of the input variables, and only give their types • What about the stuff in braces? – It’s the body of function main, its definition
- 8. CSE 332: C++ program structure and development environment What’s cout << “hello, world!” << endl; ? • Uses the standard output iostream, named cout – For standard input, use cin – For standard error, use cerr • << is an operator for inserting into the stream – A member operator of the ostream class – Returns a reference to stream on which its called – Can be applied repeatedly to references left-to-right • “hello, world!” is a C-style string – A 14-postion character array terminated by ‘0’ • endl is an iostream manipulator – Ends the line, by inserting end-of-line character(s) – Also flushes the stream
- 9. CSE 332: C++ program structure and development environment What about return 0; ? • The main function should return an integer – By convention it should return 0 for success – And a non-zero value to indicate failure • The program should not exit any other way – Letting an exception propagate uncaught – Dividing by zero – Dereferencing a null pointer – Accessing memory not owned by the program • Indexing an array “out of range” can do this • Dereferencing a “stray” pointer can do this
- 10. CSE 332: C++ program structure and development environment A Slightly Bigger C++ Program #include <iostream> using namespace std; int main (int argc, char * argv[]) { for (int i = 0; i < argc; ++i) { cout << argv[i] << endl; } return 0; }
- 11. CSE 332: C++ program structure and development environment int argc, char * argv[] • A way to affect the program’s behavior – Carry parameters with which program was called – Passed as parameters to main from crt0 – Passed by value (we’ll discuss what that means) • argc – An integer with the number of parameters (>=1) • argv – An array of pointers to C-style character strings – Its array-length is the value stored in argc – The name of the program is kept in argv[0]
- 12. CSE 332: C++ program structure and development environment for (int i = 0; i < argc; ++i) • Standard (basic) C++ for loop syntax – Initialization statement done once at start of loop – Test expression done before running each time – Expression to increment after running each time • int i = 0 – Declares integer i (scope is the loop itself) – Initializes i to hold value 0 (not an assignment!) • i < argc – Tests whether or not we’re still inside the array! – Reading/writing memory we don’t own can crash the program (if we’re really lucky!) • ++i – increments the array position (why prefix?)
- 13. CSE 332: C++ program structure and development environment {cout << argv[i] << endl;} • Body of the for loop • I strongly prefer to use braces with for, if, while, etc., even w/ single-statement body – Avoids maintenance errors when adding/modifying code – Ensures semantics/indentation say same thing • argv[i] – An example of array indexing – Specifies ith position from start of argv
- 14. CSE 332: C++ program structure and development environment Lifecycle of a C++ Program C++ source code Makefile Programmer (you) object code (binary, one per compilation unit) .o make “make” utility xterm console/terminal/window Runtime/utility libraries (binary) .lib .a .dll .so gcc, etc. compiler link linker E-mail executable program Eclipse debugger precompiler compiler turnin/checkin An “IDE” WebCAT Visual Studio window
- 15. CSE 332: C++ program structure and development environment Development Environment Studio • We’ll follow a similar format most days in the course – Around 30 minutes of lecture and discussion – Then about 60 minutes of studio time – Except for open studio/lab days, reviews before the midterm and final, and the day of the midterm itself • In the studios, please work in groups of 2 or 3 – Exercises are posted on the course web page – Record your answers to the exercises, and e-mail your answers to the course account when you’re done – We’ll migrate throughout the studio to answer questions • Use studio time to develop skills and understanding – A good chance to explore ideas you can use for the labs – Exams will test understanding of the studio material – You’re encouraged to try variations beyond the exercises