How to write C program without 'main'?

How to write C program without using Main...! When I'm lear开发者_运维知识库ning how to write ASM file by for a simple C file [of length 3 lines], I got this doubt. I assembly file I used preamble and post ambles, at function.

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There is a great article and creating the smalest possible elf binary here. It has a lot of info of what is required to have something runnable by the os.

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This is logical trick. Those who are unaware of it, can learn this trick.

#include<stdio.h>
#include<conio.h>
#define decode(s,t,u,m,p,e,d) m##s##u##t
#define begin decode(a,n,i,m,a,t,e)
void begin()
{
    clrscr();
    printf("\nHello !!! Kaushal Patel.");
    getch();
}

Explanation :
The pre-processor directive #define with arguments is used to give an impression that the program runs without main(). But in reality it runs with a hidden main().

The ‘##‘ operator is called the token pasting or token merging operator. That is how, I can merge two or more characters with it.

#define decode(s,t,u,m,p,e,d) m##s##u##t

The macro decode(s,t,u,m,p,e,d) is being expanded as “msut” (The ## operator merges m,s,u & t into msut). The logic is when I pass (s,t,u,m,p,e,d) as argument it merges the 4th,1st,3rd & the 2nd characters.

#define begin decode(a,n,i,m,a,t,e)

Here the pre-processor replaces the macro “begin” with the expansion decode(a,n,i,m,a,t,e). According to the macro definition in the previous line the argument must be expanded so that the 4th, 1st, 3rd & the 2nd characters must be merged. In the argument (a,n,i,m,a,t,e) 4th,1st,3rd & the 2nd characters are ‘m’,’a’,’i’ & ‘n’.

So the third line “void begin” is replaced by “void main” by the pre-processor before the program is passed on for the compiler.

Source : http://ctechnotips.blogspot.in/2012/04/writing-c-c-program-without-main.html

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Here is your answer:->

#include <stdio.h>

extern void _exit(register int);

int _start(){

printf(“Hello World\n”);

_exit(0);

}