c語言 宏定義 去除宏定義

To check whether a Macro is defined or not in C language – we use #ifdef preprocessor directive, it is used to check Macros only.

要檢查是否用C語言定義了宏 -我們使用#ifdef預處理程序指令，它僅用于檢查宏。

Syntax:

句法：

    #ifdef MACRO_NAME
//body
#endif 

If MACRO_NAME is defined, then the compiler will compile //body (a set of statements written within the #ifdef ... #endif block).

如果定義了MACRO_NAME ，則編譯器將編譯// body (在#ifdef ... #endif塊中編寫的一組語句)。

Example:

例：

#include <stdio.h>
#define NUM 100
int main()
{
//checking a defined Macro 
#ifdef NUM
printf("Macro NUM is defined, and its value is %d\n",NUM);
#else
printf("Macro NUM is not defined\n");
#endif 
//checking an undefined Macro 
#ifdef MAX
printf("Macro MAX is defined, and its value is %d\n",MAX);
#else
printf("Macro MAX is not defined\n");
#endif     
return 0;
}

Output

輸出量

    Macro NUM is defined, and its value is 100Macro MAX is not defined

翻譯自: https://www.includehelp.com/c-programs/check-whether-a-macro-is-defined-or-not-in-c.aspx

c語言 宏定義 去除宏定義