#if defined MACRO 是否等同于#ifdef MACRO?

问题描述

我的代码有两种模式，debug 和 verbose.我在头文件中将它们定义为，

I have code that I want to have two modes, debug and verbose. I define them in my header file as,

#define verbose TRUE
#define debug TRUE

到目前为止，在我的代码中，我一直在使用

In my code so far, I have just been using

#if(debug)
  //code
#endif

但是使用起来更合适吗?

but is it more proper to use?

#ifdef debug
  // code
#endif

我读过一些关于预处理器宏的文章，但当时并没有什么意义.所以，我有一个问题:#if defined MACRO 是否等同于#ifdef MACRO?哪个更适合启用/禁用特定代码部分?

I read something about preprocessor macros but it didn't make sense at the time. So, I have a question: Is #if defined MACRO equivalent to #ifdef MACRO? and which one is better for enabling/disabling a particular section of code?

推荐答案

#ifdef MACRO
#if defined (MACRO)

会做同样的事情.但是，已定义 (MACRO) 只是一个表达式，在 #if 内部计算为 0 或 1，它可以与其他表达式组合.例如

will do the exact same thing. However, the defined (MACRO) is just an expression that evaluates to 0 or 1 inside the #if, and it can be combined with other expressions. For example

#if defined (MACRO) && ! defined (MACRO2)
    // Do this
#else
    // Do that
#endif

尝试使用#ifdef 执行此操作 - 除非您的代码变得非常笨拙，否则您不能这样做.

Try doing that with #ifdef - you can't unless your code gets really clumsy.

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