c – 是否可以从宏定义宏

2019年7月21日 281次阅读

这就是我的想法.

#define prefix_1 1
#define prefix_2 2
#define prefix_3 3

我想用上面的前缀定义一个宏 – 比如宏macro_prefix_1 macro_prefix_2 – 我希望它们变成macro_1 macro_2等.就像下面的代码一样

#define macro_##prefix_1 I_am_macro_1
#define macro_##prefix_2 I_am_macro_2

这可能吗？

最佳答案 不幸的是,你要做的事情是不可能的. (##)指令在宏声明中是不可能使用的.只能在定义中使用它.

#define glue(a,b) a ## b
glue(c,out) << "test";

从cplusplus.com借来的例子

下面,我写了一个你想做的例子.

#include <stdio.h>

#define prefix_1 1
#define prefix_2 2
#define prefix_3 3

#define macro_##prefix_1 "macro_1"
#define macro_##prefix_2 "macro_2"
#define macro_##prefix_3 "macro_3"

int main(){
    printf("%s\n%s\n%s\n", macro_prefix_1, macro_prefix_2, macro_prefix_3);
    return 0;
}

当您尝试编译上面的代码时,您将获得此构建日志.

||=== Build: Debug in file_test (compiler: GNU GCC Compiler) ===|
main.cpp|7|warning: missing whitespace after the macro name [enabled by default]|
main.cpp|7|error: '##' cannot appear at either end of a macro expansion|
main.cpp|8|warning: missing whitespace after the macro name [enabled by default]|
main.cpp|8|error: '##' cannot appear at either end of a macro expansion|
main.cpp|9|warning: missing whitespace after the macro name [enabled by default]|
main.cpp|9|error: '##' cannot appear at either end of a macro expansion|

main.cpp||In function 'int main()':|
main.cpp|13|error: 'macro_prefix_1' was not declared in this scope|
main.cpp|13|error: 'macro_prefix_2' was not declared in this scope|
main.cpp|13|error: 'macro_prefix_3' was not declared in this scope|
||=== Build failed: 6 error(s), 3 warning(s) (0 minute(s), 0 second(s)) ===|

因此,如果您希望能够拥有宏,则必须正常添加前缀.幸运的是,你基本上已经这样做了,但添加了“##”.希望这有帮助.

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