C program without main

Yes it is possible to write a program in c without using main.

Here is the code:
/* prog_without_main.c */
_start()
{
_exit(my_main());
}

int my_main(void)
{
printf(“Hello\n”);
return 42;
}

And use this command (% is command prompt) to compile:
%gcc -O3 -nostartfiles prog_without_main.c

Try compiling this example:

#include<stdio.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()
{
printf(“hello”);

}
here is how it works once we say define we need to understand that
#define x y
then ‘x’ ix replaced by ‘y’
similarly in this case
#define begin decode(a,n,i,m,a,t,e)
decode(a,n,i,m,a,t,e) is replaced by m##a##i##n
bcoz s is replaced by a,t by n,u by i and so on
s->a
t->n
u->i
m->m
p->a
e->t
d->e
now the statement becomes
void m##a##i##n
And u must be knowing that ## is used for string concatenation so it becomes
“main”
finally the code crops down to
void main()
{
printf(“hello”);
}

Filed under: Basic, Functions & Structures