C -- Print To Screen Without #include <stdio.h>? [closed] - c

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Closed 11 years ago.
Is there a way to have a C source file print to the screen without including <stdio.h>?
Here's my situation: I was asked to programatically handle 1000 C source files that will each implements several numerical functions in C (these functions are supposed to work on data that is in memory, eithout any I/O). The origin of these source files in unclear, and hence, I'd like to make sure there will be no harm to my machine when I compile & run these source files.
Is there a way to find out if a C source file is potentially harmful? I thought of asking the developers to avoid any #include statements whatsoever, but I do need just printf -- as I'd like them to include an output of their calculations within main().
Any ideas?

Answer 1

Sure, add the prototype for printf at the top of your source file, as long as you're linking to the CRT libraries you can use the function without including stdio.h
printf prototype
int printf ( const char * format, ... );

Answer 2

There are, though they are probably a bit larger than the scope of the format of SO. In essence you leverage assembler calls in C. The blog KSplice touches on the subject ( with code and examples ) here.

Answer 3

Is there a way to find out if a C source file is potentially harmful?
No, there is none. A malicious source file could possibly do anything it wanted by defining its own prototypes, or by using inline assembly -- #include is just a compile-time convenience.

Answer 4

I would like to clarify why we need printf and studio.h to maybe make the concept more clear. C is a portable language. You can compile c for Linux, Mac OSX, Windows. In each, causing output normally boils down to a system call, or in embedded systems, dealing directly with a frame buffer or Uart device.
So of course it is possible, do you want to do it? Depends why. If you are coding against a specific platform and dont have printf(), then you may have to look into invoking a system call directly for that platform/writing some platform specific assembly code. It all depends on your use case.

Answer 5

Sure, put the necessary function prototypes in your program.
If you mean by not using printf, then you have several options - you can use fwrite, or you could dispense with streams and use write, or you could invoke operating system I/O services directly, or perhaps you could talk to the display hardware directly, or many other things.
If you want a better answer, perhaps explain why you want to not include stdio.h

Answer 6

This is silly but still:
#include <string.h>
int main() {
puts ("hi");
return 0;
}
and Output:
$ gcc -o try try.c
$ ./try
hi