the structure of the main function in C

portia · 09-22-2010, 09:46 AM

I have started learning C and am following Ivor Horton's "Beginning C - From Novice to Professional".

I've noticed that in the book the structure of the main function is:

int main (void)

however on the internet I found a lot of cases:

void main (void)

Which one is preferred and why?

Thank you

JohnGraham · 09-22-2010, 10:13 AM

Quote:

Originally Posted by portia

I have started learning C and am following Ivor Horton's "Beginning C - From Novice to Professional".

I've noticed that in the book the structure of the main function is:

int main (void)

however on the internet I found a lot of cases:

void main (void)

Which one is preferred and why?

Thank you

It doesn't matter, unless you want to look at the return value of your program (from bash, enter "echo $?" as the next command after you run your program). If you use "int main(void)" then what you return from main() will be the return value of your program - if you use "void main(void)" you'll get some random return value.

In general, just use "int main(void)" and return 0 when things go well, 1 when things don't. Programs on *nix generally expect this behaviour.

Wim Sturkenboom · 09-23-2010, 12:10 AM

In future you might also encounter the following

Code:

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

argc gives the number of arguments and argv is an array containing those arguments. This way, a program can take command line arguments.

Code:

#include <stdio.h>

int main(int argc, char *argv[])
{
int cnt;
    printf("%d argument%s\n",argc,argc==1?"":"s");

    for(cnt=0; cnt < argc; cnt++)
    {
        printf("%s\n",argv[cnt]);
    }

    return 0;
}

Code:

wim@btd-techweb01:~/forums_linuxquestions/lq833796$ ./a.out hi there
3 arguments
./a.out
hi
there
wim@btd-techweb01:~/forums_linuxquestions/lq833796$ ./a.out "hi there"
2 arguments
./a.out
hi there
wim@btd-techweb01:~/forums_linuxquestions/lq833796$

MTK358 · 09-23-2010, 07:54 AM

NEVER use "void main()". It's just plain wrong, but some compilers tolerate it.

gozlemci · 09-23-2010, 01:46 PM

MTK358;
While I was learning C, I realized that most books use "int main." However you have strongly not recommend to use "void main." Why?

dugan · 09-23-2010, 01:48 PM

http://www.parashift.com/c++-faq-lit....html#faq-29.3

Because it's not valid C. This is can be confirmed by reading the standard.