Question

I just saw this thread, describing how to add conditional macros: Conditional value for a #define

但就我的情况而言,我正在确定一项职能。

#if TARGET_IPHONE_SIMULATOR

#define doSomething(){
    \ does something
}

#else

#define doSomething(){
    \ does something else
}

#endif

这样做确实可行,但我却使编审员屈服于这一警告:

"doSomething" redefined
This is the location of the previous arguments

是否有任何工作帮助消除警告?

<><>UPDATE:

因此,我试图在我的定义中列入条件:

#define doSomething(){

#if TARGET_IPHONE_SIMULATOR
    \ do something
#else 
    \ do something else
#endif

}

但是,这犯了一个错误:

error:  #  is not followed by a macro parameter.

Answer 1

我找到了对我问题的答复:here。

Conclusion: you cannot include #ifdef etc... inside #define, because there should only be one pre-processing directive per line.

So although we can break the line with a backslash this helps writing readable multiline macros, but the preprocessor will see it as one line:

#define doSomething(){ #if TARGET_IPHONE_SIMULATOR ... #endif }

造成这一错误的:

error:  #  is not followed by a macro parameter.

这是有意义的,因此,我必须重新思考我的执行。

Answer 2

Also, this might address the error you received:
# and ## have special purposes inside macro definitions. # is used to surround a macro parameter with double quotes. ## is used to concatenate two macro parameters. Example:
#define ABC(X) #X
ABC(hello) results in "hello".
#define XYZ(X,Y) X##Y
XYZ(O,K) results in OK. Note that this feature is (possibly) unique to ANSI C.
Also, why would you be using a macro like this? Might a function work better for you?

Answer 3

你们的想法是比照/延伸。罗马语必须被视为类似于功能的宏观。因此,其定义模糊不清。摘录如下:

doSomething() {
#if TARGET_IPHONE_SIMULATOR
   // conditionally compiled code
#else
   // platform-specific code
#endif
}

Answer 4

考虑的一个选择是,在一个将及时解决的宏观中创造条件。考虑如下:

If I would like to call a different function based on the value of c as a pre-processor action, I can define a macro that checks the value of c statically.

#define AorB(c) ((c>0) ? (Do_A(c)) : (Do_B(c)))

那么,如果你把一个最优化的等级混为一谈,把永远无法达到的分行移走,那么就应该排除哪一种情况。这并不是你所期待的。

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