Thread: int main vs void main

Originally Posted by Elysia

I am not aware of any standard in either C or C++ that allows the use of void main (though technically there was a possibility in C90).
Many embedded compilers are often non-standard.

Originally Posted by C99 5.1.2.1 p1

In a freestanding environment (in which C program execution may take place without any
benefit of an operating system), the name and type of the function called at program
startup are implementation-defined. Any library facilities available to a freestanding
program, other than the minimal set required by clause 4, are implementation-defined.

Emphasis mine. It doesn't even have to be called main, let alone return an int.

EDIT: Guess Jim got there first.

From the C++ 0x draft standard.

3.6
Start and termination
3.6.1
1
Main function
[basic.start]
[basic.start.main]
A program shall contain a global function called main, which is the designated start of the program. It
is implementation-defined whether a program in a freestanding environment is required to define a main
function. [ Note: In a freestanding environment, start-up and termination is implementation-defined; start-
up contains the execution of constructors for objects of namespace scope with static storage duration;
termination contains the execution of destructors for objects with static storage duration. — end note ]

Jim

Originally Posted by Annonymous

Recently, I am seeing a lot of people use void main() instead of int main. Is this a good practice? I use int main, isn't that the correct way? Unless, your trying to shut off warnings about main not returning a value. What are the pros/cons? Which is better?

It's not a choice. The correct forms of main are either...

Code:

int main (void)
  {

    return errorlevel;  // usually 0
}

or

Code:

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

     return errorlevel;  //usually 0
}

Although it's apparently not taught in class... the operating system actually does make use of the return value of main() ... It's used in batch files and shell scripts, it's used when one program launches a child program and so on.

If you use void main() and do not return a value, the address reserved for the return value is uninitialized, basicially containing a random number, and can cause wild misbehaviors in cases where a return value is expected.

Originally Posted by Annonymous

Ok, if this is not good practice. Why are people using it? Any ideas? Could the colleges possibly be teaching this practice?

Yes, they are... Many schools, especially in India, are hopelessly out of date; still teaching with Turbo C (a 16 bit compiler who's output won't even ruin on 64 bit windows) and course designs that date back to MS-DOS.