#if和#ifdef Objective-C预处理器宏之间的区别是什么?

How to define preprocessor macros in build settings, like IPAD_BUILD, and IPHONE_BUILD (and how to use them in my factory methods)?

如何在构建设置中定义预处理器宏，比如IPAD_BUILD和IPHONE_BUILD(以及如何在我的工厂方法中使用它们)?

I'm using these by heart now, would be cool to know what is going behind.

我现在把这些都记在心里了，如果知道后面发生了什么就好了。

2 个解决方案

#1

/#if works as usual if:

/#if如:

#if __IPHONE_OS_VERSION_MAX_ALLOWED >= 30200
  if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad) {
    return YES;
  }
#endif
  return NO;
}

/#ifdef means "if defined - some value or macros":

/#ifdef表示“if defined - some value or macros”:

#ifdef    RKL_APPEND_TO_ICU_FUNCTIONS
#define RKL_ICU_FUNCTION_APPEND(x) _RKL_CONCAT(x, RKL_APPEND_TO_ICU_FUNCTIONS)
#else  // RKL_APPEND_TO_ICU_FUNCTIONS
#define RKL_ICU_FUNCTION_APPEND(x) x
#endif // RKL_APPEND_TO_ICU_FUNCTIONS

or:

或者:

#ifdef __OBJC__
    #import <Foundation/Foundation.h>
#endif

Use this link for more information http://www.techotopia.com/index.php/Using_Objective-C_Preprocessor_Directives

更多信息请使用此链接http://www.techotopia.com/index.php/using_objective - c_preprocessor_directive

To test whether you running iPad or not you should have smth like this:

要测试你是否运行iPad，你应该有以下smth:

#define USING_IPAD UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad

if (USING_IPAD) {
    NSLog(@"running iPad");
}

Here's another useful preprocessor functions:

下面是另一个有用的预处理函数:

#ifdef DEBUG
    //here we run application through xcode (either simulator or device). You usually place some test code here (e.g. hardcoded login-passwords)
#else
    //this is a real application downloaded from appStore
#endif

#2

A macro can be undefined, it can be defined with no value, or it can be defined with some value, possibly a number. Examples:

宏可以是无定义的，可以是无值的，也可以是有值的，可能是一个数字。例子:

#undef MACRO
#define MACRO
#define MACRO ??????
#define MACRO 0
#define MACRO 1

#ifdef MACRO or #if defined (MACRO) checks whether the macro is defined, with or without value.

#ifdef宏或#if defined(宏)检查是否定义了宏，是否有值。

#if MACRO substitutes the macro definition; if the macro is not defined then it substitutes 0. It then evaluates the expression that it find. If we take the five examples above, #if MACRO will be turned into

#如果宏替换了宏定义;如果宏没有定义，那么它将替换0。然后计算它找到的表达式。如果我们以上面的五个例子为例，# If宏将被转换为

#if 0
#if
#if ??????
#if 0
#if 1

Number 2 and 3 give a compile time error. Number 1 and 4 evaluate to false, so the following code is skipped. Number 5 evaluates to true.

2和3给出一个编译时间错误。1和4的值为false，因此跳过以下代码。5的值为true。

#if is more flexible: You could write

#if更灵活:你可以写作

#if MACRO == 2

which will only compile the following code if the macro was defined for example as

如果宏被定义为

#define MACRO 2

#1