...bir tane C başlık dosyamız olsun.

```c
#ifndef KAT_H
#define KAT_H

#define UC...

...SOCKET;
#else
typedef unsigned int SOCKET;
#endif

#ifndef FD_SETSIZE
#define FD_SETSIZE      64
#endif...

...h> directly; include <byteswap.h> instead."
#endif

#ifndef _BITS_BYTESWAP_H
#define _BITS_BYTESWAP_H...

...c) 2012 Apple Inc. All rights reserved.
 * [...]
 */
#ifndef _INT8_T
#define _INT8_T
typedef __signed...

...feature A enabled");
    }

}

```

Unfortunatly there is not #ifndef, so in case you want to make...

...not. They can be used like this:

#ifndef __has_feature         // Optional of course.
  #define __has...

...Have_Qsort_R = true;
```

gcc/config.c
```
#ifndef GCC_CONFIG_H
#define GCC_CONFIG_H...

...Have_Qsort_R = true;
```

gcc/config.h
```
#ifndef GCC_CONFIG_H
#define GCC_CONFIG_H...

...bool expr) {...}
```

library.c
```
include "config.h"
#ifndef USE_MY_ASSERT
    void MY_ASSERT(bool...

...include guard idiom:

// This is foo.h
#ifndef INCLUDED_FOO_H_
#define INCLUDED_FOO_H...