C语言 #ifdef 里面 #define
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#ifdef inside #define
提问by agent.smith
I am trying to write something like this:
我正在尝试写这样的东西：
#define COV_ON(x) \
#ifdef COVERAGE_TOOL \
_Pragma (COVERAGE #x)
#endif
Is there any way to define COV_ONlike this? I know what I have done above is wrong as I can't have #ifdefinside #define. (#is not an allowed character in #define).
So is there any solution?
有没有办法COV_ON像这样定义？我知道我在上面所做的事情是错误的，因为我不能#ifdef在#define 中进行操作。(#中不允许使用的字符#define)。那么有什么解决办法吗？
回答by Hans Passant
Not possible. Do it the other way around:
不可能。反过来做：
#ifdef COVERAGE_TOOL
#define COV_ON(x) _Pragma (COVERAGE #x)
#else
#define COV_ON(x)
#endif
回答by Philip
Simply turn it around:
简单地扭转它：
#ifdef COVERAGE_TOOL
#define COV_ON(x) _Pragma (COVERAGE #x)
#else
#define COV_ON(x) /* foo */
#endif
回答by technosaurus
This is an old question, but it needed an up to date answer.
这是一个古老的问题，但它需要一个最新的答案。
Instead of using an inline ifdef within the macro you can selectively define a __VA_ARGS__macro to do the same thing
您可以有选择地定义一个__VA_ARGS__宏来做同样的事情，而不是在宏中使用内联 ifdef
#ifdef COVERAGE_TOOL
#define IF_COVERAGE_TOOL(...) __VA_ARGS__
#else
#define IF_COVERAGE_TOOL(...)
#endif
#define COV_ON(x) IF_COVERAGE_TOOL( _Pragma (COVERAGE #x) )
This has similar functionality to an ifdef except that you get parentheses to delineate the beginning and end (which most IDEs have no problems code-folding) While you can still use #defineand #ifdefwithin the context, #includeis not allowed. In order to get inline capabilities similar to #else, you can define a corresponding macro like this:
这与 ifdef 具有类似的功能，除了您使用括号来描述开头和结尾（大多数 IDE 代码折叠没有问题）虽然您仍然可以在上下文中使用#define和，但这是不允许的。为了获得类似于 的内联功能，您可以像这样定义相应的宏：#ifdef#include#else
//#define FOO
#ifdef FOO
#define IF_FOO(...) __VA_ARGS__
#define NO_FOO(...)
#else
#define IF_FOO(...)
#define NO_FOO(...) __VA_ARGS__
#endif
IF_FOO(
#define BAR 5
int foo = BAR;
)
NO_FOO(
#define foo 5
)
Only one of NO_FOO()/IF_FOOwill produce code.
只有其中之一NO_FOO()/IF_FOO会产生代码。
OK, that's a handy hack, but can we make it MOREuseful than #ifdefs... Boolean logic and configuration perhaps? Lets set up some truth tables (and a couple helper macros).
OK，这是一个方便的黑客，但我们可以让更多有用比#ifdefs...布尔逻辑和配置吧？让我们设置一些真值表（和几个辅助宏）。
#define PASTE_(x,y) x##y
#define PASTE(x,y) PASTE_(x,y)
#define PASTE3_(x,y,z) x##y##z
#define PASTE3(x,y,z) PASTE3_(x,y,z)
#define Y(...) __VA_ARGS__
#define N(...)
#define IF(x) x //alternate method similar to IFNOT()
#define NOT_N Y
#define NOT_Y N
#define IF_NOT(x) PASTE(NOT_,x)
#define NOT(x) PASTE(NOT_,x)
#define N_OR_N N
#define N_OR_Y Y
#define Y_OR_N Y
#define Y_OR_Y Y
#define OR(x,y) PASTE3(x,_OR_,y)
#define N_AND_N N
#define N_AND_Y N
#define Y_AND_N N
#define Y_AND_Y Y
#define AND(x,y) PASTE3(x,_AND_,y)
#define N_XOR_N N
#define N_XOR_Y Y
#define Y_XOR_N Y
#define Y_XOR_Y N
#define XOR(x,y) PASTE3(x,_XOR_,y)
#define N_NOR_N Y
#define N_NOR_Y N
#define Y_NOR_N N
#define Y_NOR_Y N
#define NOR(x,y) PASTE3(x,_NOR_,y)
#define N_NAND_N Y
#define N_NAND_Y Y
#define Y_NAND_N Y
#define Y_NAND_Y N
#define NAND(x,y) PASTE3(x,_NAND_,y)
#define N_XNOR_N Y
#define N_XNOR_Y N
#define Y_XNOR_N N
#define Y_XNOR_Y Y
#define XNOR(x,y) PASTE3(x,_XNOR_,y)
#define IF2(x,y,z) PASTE3(x,y,z)
config.h
配置文件
#define FOO Y
#define BAR N
#define BAZ Y
code.c
代码.c
AND(FOO,BAR)(/*do stuff if both FOO and BAR are enabled*/)
IF2(FOO,_AND_,BAR)( /*do stuff if both FOO and BAR are enabled*/ )
OR(BAZ,AND(FOO,BAR))(
/*do stuff if both FOO and BAR are enabled or BAZ is enabled*/
)
回答by EboMike
#ifdef COVERAGE_TOOL
#define COV_ON(x) _Pragma (COVERAGE #x)
#else
#define COV_ON(x)
#endif
回答by sam hocevar
You cannot. But you can swap #ifdefand #define:
你不能。但是你可以交换#ifdef和#define：
#ifdef COVERAGE_TOOL
# define COV_ON(x) _Pragma (COVERAGE #x)
#else
# define COV_ON(x)
#endif
回答by jberg
As you mentioned it is not possible to have an #ifdef in a #define. What you should do instead is reverse the order:
正如您所提到的，#define 中不可能有 #ifdef。你应该做的是颠倒顺序：
#ifdef COVERAGE_TOOL \
#define COV_ON(x) \
etc.
#endif
