Thread: Questions about a mass amount of headers

Hi i had a theory question i guess? if its called that I wanted to know what do u do when theres a bunch of class files and eventually u accidentally rewrite a header file for one class thats already redefine in another class. basically how do u avoid recalling the same header files over again with a mass of files. Im not sure if what im looking for is

#ifndef BAR_H
#define BAR_H

And this is too avoid the errors and warnings about already defined functions and variables

That's how I do it...

Code:

#ifndef HEADER_H
#define HEADER_H

... huge mass of stuff...


#endif // HEADER_H

Also many compilers support #pragma once instead, but I'm not sure if that's part of the standards or not.

Yea i actually wanted to know what #pragma once does cuz i tried googling it up and didnt find anything that could explain it to me i thought that was a good method but i used it on an itnerview and they didnt like it or thought it was completely different to use for this situation

I use Pelles C and beginning with ver 5.0 (now at 6.0) it supports the "#pragma once" as a means of ensuring you don't double-read headers. It is pre-included in the windows headers but you need to put it in your own headers manually.

I don't see it in my copy of the C-99 standard so if your interviewer knew the standard well, he might not be pleased to see you using non standard code.

Originally Posted by Elysia

It's not standard. All #pragma are compiler-specific.
I'm not sure to what the original question is. Include guards are used to guard against a header being included multiple times in one translation unit (read: source file). This protects against multiple definitions errors.

Also, simply HEADER_H might not be unique enough. I recommend putting time and date into it to make it unique. Eg:

#ifndef MY_HEADER_H_20101007_0930
...

HEADER_H was only an example, used to clarify the concept.