A simple C program without #include <stdio.h>

Question

How to call "printf" directly without including stdio.h ?

I found a interesting tutorial here:
http://www.halcode.com/archives/2008/05/11/hello-world-c-and-gnu-as/

So, here's my attempt:

int main(){
 char ss[] = "hello";

 asm (
  "pushl %ebp ;"
  "movl %esp, %ebp ;"
  "subl $4, %esp ;"
  "movl $ss, (%esp) ;"
  "call _printf ;"
  "movl  $0, %eax ;"
  "leave ;"
  "ret ;"
 );

 return 0;
}

I'm using MinGW 4.4, and here's how I compile it:

gcc -c hello.c -o hello.o
ld hello.o -o hello.exe C:/mingw/lib/crt2.o C:/mingw/lib/gcc/mingw32/4.4.0/crtbegin.o C:/mingw/lib/gcc/mingw32/4.4.0/crtend.o -LC:/mingw/lib/gcc/mingw32/4.4.0 -LC:/mingw/lib -lmingw32 -lgcc -lmsvcrt -lkernel32

Unfortunately, it fails:

hello.o:hello.c:(.text+0x26): undefined reference to `ss'

How to fix this?

Answer 1

You can copy the declaration of printf into your program. In C, including other file is a mere copy-pasting its text into your program. So you can do this job by doing the copy-paste on your own.

extern int printf (const char* format, ...);

int main()
{
  printf("Hello, world!\n");
  return 0;
}

Linker will surely find the proper definition in the libraries, against which you program is linked by default.

Answer 2

int main() {

    char ss[] = "hello";
    char *p = ss;

    asm (
        "movl %0, (%%esp);"
        "call _printf;" : "=r" (p)
    );

    return 0;
}

Answer 3

int main(void)
{
    char ss[] = "hello";

    __asm(
        "pushl %[ss]\n"    // push args to stack
        "call _puts\n"
        "addl $4, %%esp\n" // remove args from stack
        :: [ss] "r" (ss)   // no output args, no clobbered registers
    );

    /*  C equivalent:
        extern int puts(const char *);
        puts(ss);
    */
}

Answer 4

Its very ease Write one c program using printf statement then save the program with .c extension and Run the program It will work.... Even it can contain function like clrscr(), getch() which are part of conio.h