8

I wanted to print something using printf() function in C, without including stdio.h, so I wrote program as : 

int printf(char *, ...);
int main(void)
{
        printf("hello world\n");
        return 0;
}

Is the above program correct ?

Happy Mittal
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    Your format string should be `const char*`. You could just locate `stdio.h` and read the definition there. Why, out of curiosity, don't you want to `#include `? – user229044 Nov 14 '10 at 18:30
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    how do you expect to print anything on the screen without including stdio.h ?? You'll have to write your own libraries .. it's suicidal :) – sdadffdfd Nov 14 '10 at 18:31
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    @bemace @Vic The act of including `stdio.h` doesn't link anything, header files don't work that way. This question is completely valid, and will work just fine. – user229044 Nov 14 '10 at 18:32
  • @meager : It was just a quiz question. – Happy Mittal Nov 14 '10 at 18:34

5 Answers5

19

The correct declaration (ISO/IEC 9899:1999) is:

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

But it would be easiest and safest to just #include <stdio.h>.

CB Bailey
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13

Just:

man 3 printf

It will tell you printf signature:

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

this is the right one.

peoro
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4

I have no idea why you'd want to do this.

But it should be const char *.

Oliver Charlesworth
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  • @Oli : Does only char* affect anything ? – Happy Mittal Nov 14 '10 at 18:35
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    @Charles: In C99, yes. That won't compile for anything earlier. – Oliver Charlesworth Nov 14 '10 at 18:35
  • @Charles Just `const char*` here. – user229044 Nov 14 '10 at 18:35
  • @Happy Yes, it defines a completely different function than `printf(const char*,...)`. – user229044 Nov 14 '10 at 18:36
  • @meager : If I don't write const, then isn't it guaranteed that library's printf is called ? – Happy Mittal Nov 14 '10 at 18:39
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    @meagar: This is not C++. I agree it's *wrong* to omit the `const`, but it does not "define a completely different function", only an incorrect prototype for the same function. (I suspect this wrong prototype is actually guaranteed to work anyway, but I'm not sure.) – R.. GitHub STOP HELPING ICE Nov 14 '10 at 18:56
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    @Happy Mittal: If you don't include all the required type qualifiers then you have provided a function prototype that isn't compatible with the function definition. C doesn't have function overloading so you can't be referring to any other function but attempting to call it with an incompatible prototype in scope technically leads to undefined behaviour. – CB Bailey Nov 14 '10 at 18:57
0

Here is another version of the declaration:

extern int printf (__const char *__restrict __format, ...);
Zorayr
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-3
int printf(char *, ...);

works just fine, I don't know why people are telling you that char needs to be a const

lkl
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