I have the following C program (as simple as it gets):
#include <stdio.h>
main()
{
printf("Test");
}
But using the gcc compiler within Cygwin, I cannot get this program to work unless I make the following modifications:
#include <stdio.h>
int main()
{
printf("Test");
return 0;
}
Could anyone explain why? What is so special about the "int" and the "return 0;" ?
Thanks! Amit
With C you are always required to specify your output type. So the int is always required (with some compilers, void will work too).
The "normal" minimal version is this:
int main(int argc, char **argv){
return 0;
}
Depending on your system you could also have a char **envp and char **apple there aswell.
http://en.wikipedia.org/wiki/Main_function_(programming)#C_and_C.2B.2B
argc and argv arguments ;).
void is not an allowed return type in any C or C++ standard.
argc and argv are required.
int main(void) must be accepted by conforming C (and C++) compilers.int is the required return type for main per the C standard.
return 0; doesn't prevent main from returning an unspecified values because "[...] reaching the } that terminates the main function returns a value of 0." (ISO/IEC 9899:1999 5.1.2.2.3)
main without encountering a return statement, the effect is that of executing return 0;" (ISO/IEC 14882:2003 3.6.1 [basic.start.main] / 5)The int is a return code. I believe C defaults to returning 0. Generally speaking a return of 0 means successful completion of program while 1,2,3... would be error codes. It is often used by programs that want to test if the program ran successfully.
intis the return type for the function, in this case the main(). As you know, you always need to specify the return type of a function in C (it could be void; there you don't need to return anything)!
When your function has a return type (int, for example), you are obligated to put a return sentence (return 0;, for example). In C, is a "standard" to return 0 when a function executed correctly. Also, when you run your program, you can obtain the value returned after the execution (in this case it will be 0). If the execution of your program would terminate erroneously, then you could return any other value (-1, 1, 2, etc.) and it is easier for you to detect the error and debug it.
return 0inmainis incorrect in C (as opposed to C++), leaving out the return type should make itintby default. Your first code compiles successfully (but with warnings) on MinGW GCC 4.5 in-ansi,-std=c90and-std=c99modes.return 0;inmain()IIRC - a standards-aware compiler is then required to make it behave as if there was areturn 0;. Not that it's important...