Argument for main()

[Alien]

Hi,

I am trying to get an understanding of main( ) functions with arguements.

I read in a book where the code had some thing like this

[code=c]
int main(int argc, char *argv[])
{
/* Lines of codes in the body of main function */
}
[/code]

Question is that main always have only this arguement? Can we make up something like this?

[code=c]
int main(int x)
{
printf("%d\n", x);
}
[/code]

Regards,

Alien

[JosAH]

According to the C and C++ Standards main should have either no arguments; as in:

[code=c]
int main() { ... }
[/code]

or exactly two arguments as in:

[code=c]
int main(int argc, char** argv) { ... }
[/code]

Of course the names of the arguments can be different, but the first argument
is an int and the second argument is a pointer to an array of char pointers, each
pointing to one command line argument when the process was started.

All others, and that includes the return type of the main function induce undefined
behaviour which can be anything at all including the canonical deamons flying
out of your nose ;-)

kind regards,

Jos

[weaknessforcats]

main() can only have these arguments:
[code=c]
int main(int argc, char *argv[])
{

}
[/code]

The reason is that this is the starting point of the program and the operating system has to know how to call your main(). The first argument is always the number of strings in the second argument and argv[0] is always the program name.

By doing it this way, your main() can have unlimited arguments. They just appear as an array of strings. To use an int argument, it will appear as a string in the argv array. All you do is convert the string to an int and off you go.

[oler1s]

You have to realize that main is a very special function that gets called by the compiler crt. So you have to define the return type of main and arguments according to the C and C++ standards, or it's a bit difficult for the compiler to work with your code.

main either takes no arguments, because you don't care about the command line arguments, or it takes an int and a char** argument to hold the parsed command line arguments. That's defined, and that's what the compiler expects. Do anything else, and either it won't compile outright, or your compiler will try and put something together, and you'll have completely undefined behavior as was said before.

[Alien]

Thank you guys for the responses. It helped me a lot to understand.

Kind Regards.