What should main() return in C and C++?

What is the correct (most efficient) way to define the main() function in C and C++ — int main() orvoid main() — and why? If int main() then return 1 or return 0?

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There are numerous duplicates of this question, including:

• What are the valid signatures for C's main() function?
• The return type of main() function
• Difference between void main() and int main()?
• main()'s signature in C++
• What is the proper declaration of main()? — For C++, with a very good answer indeed.
• Styles of main() functions in C
• Return type of main() method in C
• int main() vs void main() in C

Related:

• C++ — int main(int argc, char **argv)
• C++ — int main(int argc, char *argv[])
• Is char *envp[] as a third argument to main() portable?
• Must the int main() function return a value in all compilers?
• Why is the type of the main() function in C and C++ left to the user to define?
• Why does int main(){} compile?

Answers:-

The return value for main should indicate how the program exited. Normal exit is generally represented by a 0 return value from main. Abnormal termination is usually signalled by a non-zero return but there is no standard for how non-zero codes are interpreted. Also as noted by others, void main() is explicitly prohibited by the C++ standard and shouldn't be used. The valid C++ main signatures are:

int main()

and

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

which is equivalent to

int main(int argc, char** argv)

It's also worth noting that in C++, int main() can be left without a return value at which point it defaults to returning 0. This is also true with a C99 program. Whether return 0 should be omitted or not is open to debate. The range of valid C program main signatures is much greater.

Also, efficiency is not an issue with the main function. It can only be entered and left once (marking program start and termination) according to the C++ standard. For C, the case is different and re-entering main() is allowed, but should probably be avoided.

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