C program without a main function? [closed]

Answer 1

Yes, you can.

_start function is the entry point of a C program which makes a call to main().

Going further into it, main() is the starting point of a C program from the programmer's perspective. Before calling main(), a process executes a bulk of code to "clean up the room for execution".

_start is the function which gets called first, which then allocates necessary resources and then calls main() which has to be defined by the programmer.

You can override _start and tell the compiler to not to look for main() by using "-nostartfiles" option.

#include <stdio.h> //for using printf()
_start()
{
    printf("Hello world!!\n");
    _exit(0);
}

To Compile : gcc -nostartfiles code.c -o a.out

Also look at http://linuxgazette.net/issue84/hawk.html for more basic information.

Answer 2

No. C is totally based off of the assumption that you start the program in main(). Anyway, why would you want this? This would make inconsistencies for other programmers reading your code.

Answer 3

Maybe this could work: http://www.gohacking.com/2008/03/c-program-without-main-function.html

An alternative is to write a C program and look at the Assembly output: http://users.aber.ac.uk/auj/voidmain.shtml

More information about what happens before main() is called can be found here (How Initialization Functions Are Handled): http://gcc.gnu.org/onlinedocs/gccint/Initialization.html

Answer 4

C defines the entry point in a hosted environment to be main. In a "freestanding" environment, however, the entry point can have some other name. That's about the only latitude the language (at least officially) allows in that particular respect.

Answer 5

The following linker abuse

char main[] = { /* Machine code for your target implementation */ };

will work on some platforms.