C ifdef 或
http://duoduokou.com/cplusplus/50837266774651094938.html Web#ifdef, #ifndef 检查标识符是否被定义为宏名 这就是”标识符“的意思,这两个预处理条件用来判断这个宏是否被定义,而不是宏的值。 第二个例子的错误就在于,#ifdef OPEN_AUTH 是判断OPEN_AUTH这个宏是否被定义,但从上下文看, OPEN_AUTH被定义为0,语义上就 …
C ifdef 或
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WebC语言条件编译(#if,#ifdef,#ifndef,#endif,#else,#elif) 条件编译(conditional compiling)命令指定预处理器依据特定的条件来判断保留或删除某段源代码。 例如,可 … WebMar 25, 2015 · 2 Answers. #ifdef DEBUG or #ifdef _DEBUG are used to handle some code that you use for debugging purposes. If you add #undef _DEBUG or similar to this at the very beginning of your code, the compiler will skip the code contained in #ifdef DEBUG /* bla bla */ #endif. inside this block and thinking this will work, I assure you, it won't until …
WebAug 2, 2024 · The #ifdef identifier statement is equivalent to #if 1 when identifier has been defined. It's equivalent to #if 0 when identifier hasn't been defined, or has been undefined by the #undef directive. These directives check only for the presence or absence of identifiers defined with #define, not for identifiers declared in the C or C++ source code. Web1 day ago · C语言条件编译(#if,#ifdef,#ifndef,#endif,#else,#elif). 条件编译(conditional compiling)命令指定预处理器依据特定的条件来判断保留或删除某段源代码。. 例如,可以使用条件编译让源代码适用于不同的目标系统,而不需要管理该源代码的各种不同版本。. 条件 ...
WebBelow is the syntax of #ifdef in the C programming language that has an else part as well. The definition of the macro has to be defined for the preprocessor for including the source code of C into the application which is compiled. As mentioned in the above syntax, the #ifdef directive has to be closed with an #endif directive. WebOct 26, 2012 · 1.头文件中的#ifndef头件的中的#ifndef,这是一个很关键的东西。比如你有两个C文件,这两个C文件都include了同一个头文件。而编译时,这两个C文件要一同编译 …
Web1.“与”判断 (即判断多个宏是否同时定义) #if defined(WIN32) && !defined(__LWIP_OPT_H__) && !defined(LWIP_HDR_OPT_H) #endif /* …
WebMar 9, 2024 · OR condition in #ifdef. #if defined LINUX defined ANDROID // your code here #endif /* LINUX ANDROID */. #if defined (LINUX) defined (ANDROID) // your code here #endif /* LINUX ANDROID */. Both above are the same, which one you use simply depends on your taste. P.S.: #ifdef is simply the short form of #if defined, however, does … green praying mantis with brown wingsWebAug 17, 2024 · 条件编译的指令总结如下:. #define :定义一个预处理宏. #undef :取消宏的定义. #if :编译预处理中的条件命令,相当于C语法中的if语句. #ifdef :判断某个宏是否被定义,若已定义,执行随后的语句. #ifndef :与#ifdef相反,判断某个宏是否未被定义. … green praying mantis factsWebMay 14, 2024 · C source file. In your src_file.c you need neither #ifndef nor #define.What you are implementing that way is an include guard, which is not what you want, what you actually need is:. #ifdef WITH_ATS #include "ats.h" #endif That is, to include ats.h if WITH_ATS is defined.. Note that, in your C source file, WITH_ATS is just an empty … green precision watchWebApr 10, 2024 · C++ 为什么要使用#ifdef ifdef是C++中的条件编译符号,#ifdef后面是写一个宏,如果宏已经定义泽编译,否则不编译。 C++的预处理包含宏、文件包含和条件编译 … greenpredictionsWebApr 2, 2024 · 每個巢狀 #else 、 #elif 或 #endif 指示詞都屬於最接近的上述 #if 指示詞。. 所有條件式編譯指示詞,例如 #if 和 #ifdef ,都必須符合檔案結尾之前的結尾 #endif 指示詞。. 否則會產生錯誤訊息。. 當 Include 檔包含條件式編譯指示詞時,這些指示詞必須滿足相同的條 … fly to the philippinesWebApr 12, 2024 · extern "C"的双重含义 extern 是C/C++ 语言中表明函数和全局变量作用范围(可见性)的关键字,该关键字告诉编译器,其声明的函数和变量可以在本模块或其它模块中使用。 记住下列语句: 1 extern int a; 2 C与C++的相互调用: 作为一种面向对象的语言,C++ 支持函数重载,而过程式语言C 则不支持。 fly to the scilly islesWebJan 10, 2015 · Let us presume that we have the next fragment of code in a C program: #ifdef USE_FORK CODE... #else phtread_t thread; pthread_create(&thread,NULL,clientDispatch,&client); #endif Can you explain me what are these directives, ifdef, else, endif. What happens when we use C directives? green prefab homes in california