Why do we need to use `int main` and not `void main` in C++? [duplicate]

Question

Why do we need to use int main and not void main in C++?

Answer 1

The short answer, is because the C++ standard requires main() to return int.

As you probably know, the return value from the main() function is used by the runtime library as the exit code for the process. Both Unix and Win32 support the concept of a (small) integer returned from a process after it has finished. Returning a value from main() provides one way for the programmer to specify this value.

Answer 2

Most Operating Systems report back to the user, or the calling process, if an application was successful or not. This is especially useful in scripting, where the script can conditionally branch (if-then) on the results of a program. Something along the lines of:

// pseudo-code screenscrape  http://mydatasource.com > results.txt if errorlevel == 0 then    processfile results.txt else    echo Screen Scraping Failed! end if 

This result status is done via the return value of main.

While some compilers allow for void main, for the sake of consistency and simplicity, the ANSI standard requires one single prototype of main:

int main(int argc, char *argv[]); 

Because in C, arguments are cleaned up by the caller, the author of main can neglect to declare or process the arguments argc & argv. However, if the setup-routines that call main expect an int return value, and instead don't find one, behavior can undefined.

Short answer:

• The return value of main is useful for scripting.
• The setup and cleanup routines that invoke main need a consistent interface to use.