#define st(x)      do { x } while (__LINE__ == -1) 讲解: __LINE__ 是个宏，它代表当前代码在源文件的行号，它是大于0的，所以__LINE__ == -1 等同于0,化简为： #define st(x)      do { x } while (0) Example: #define a(x) if(x) { printf("%s\n", "OK"); } int i = 1; if(0)     a(i); else     printf("%s\n", "KO"); Will expand to something equivalent to: if(0) {     if(x)     {         printf("%s\n", "OK");     }     else printf("%s\n", "KO"); } However if you define a(x) as: #define a(x) st(if(x) { printf("%s\n", "OK"); }) it will work, expanding to: if(0) {     do     {         if(x)         {             printf("%s\n", "OK");         }     }     while(0); } else printf("%s\n", "KO");

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