Communicating 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
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
config.h
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
config.h
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; }
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セクション 4. 章 1
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セクション 4. 章 1
