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bookCommunicating with the Compiler

Each #pragma directive can vary widely, but most follow a general pattern. The instruction being given is specified by the directive-name. The optional arguments depend on the specific directive and the compiler in use.

header.h

header.h

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1

            
#pragma directive-name [optional arguments]

Include Once

The old way to ensure the header is included only once is using #ifndef / #define guards. While still widely used and fully portable, it requires boilerplate and manual work.

main.c

main.c

config.h

config.h

copy

              
12345678

            
#include <stdio.h>
#include "config.h"
#include "config.h" // Reinclusion — NO duplication will occur

int main() {
    printf("%s v%s\n", APP_NAME, APP_VERSION);
    return 0;
}

Ensures that a header file is included in the compilation only once, even if it is included multiple times in different places. It is an alternative (and more modern) approach to the traditional #ifndef pattern.

main.c

main.c

config.h

config.h

copy

              
12345678

            
#include <stdio.h>
#include "config.h"
#include "config.h" // Reinclusion — NO duplication will occur

int main() {
    printf("%s v%s\n", APP_NAME, APP_VERSION);
    return 0;
}
question mark

What is the purpose of the #pragma once directive in a header file?

Select the correct answer

Var allt tydligt?

Hur kan vi förbättra det?

Tack för dina kommentarer!

Avsnitt 4. Kapitel 1

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bookCommunicating with the Compiler

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Each #pragma directive can vary widely, but most follow a general pattern. The instruction being given is specified by the directive-name. The optional arguments depend on the specific directive and the compiler in use.

header.h

header.h

copy

              
1

            
#pragma directive-name [optional arguments]

Include Once

The old way to ensure the header is included only once is using #ifndef / #define guards. While still widely used and fully portable, it requires boilerplate and manual work.

main.c

main.c

config.h

config.h

copy

              
12345678

            
#include <stdio.h>
#include "config.h"
#include "config.h" // Reinclusion — NO duplication will occur

int main() {
    printf("%s v%s\n", APP_NAME, APP_VERSION);
    return 0;
}

Ensures that a header file is included in the compilation only once, even if it is included multiple times in different places. It is an alternative (and more modern) approach to the traditional #ifndef pattern.

main.c

main.c

config.h

config.h

copy

              
12345678

            
#include <stdio.h>
#include "config.h"
#include "config.h" // Reinclusion — NO duplication will occur

int main() {
    printf("%s v%s\n", APP_NAME, APP_VERSION);
    return 0;
}
question mark

What is the purpose of the #pragma once directive in a header file?

Select the correct answer

Var allt tydligt?

Hur kan vi förbättra det?

Tack för dina kommentarer!

Avsnitt 4. Kapitel 1
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