Question

我之前使用过代码库，它有一个用于启用和禁用代码段的宏系统。它看起来像下面这样：

#define IN_USE      X
#define NOT_IN_USE  _

#if defined( WIN32 )
    #define FEATURE_A       IN_USE
    #define FEATURE_B       IN_USE
    #define FEATURE_C       NOT_IN_USE
#elif defined( OSX )
    #define FEATURE_A       NOT_IN_USE
    #define FEATURE_B       NOT_IN_USE
    #define FEATURE_C       IN_USE
#else
    #define FEATURE_A       NOT_IN_USE
    #define FEATURE_B       NOT_IN_USE
    #define FEATURE_C       NOT_IN_USE
#endif

然后功能的代码如下：

void DoFeatures()
{
#if USING( FEATURE_A )
    // Feature A code...
#endif

#if USING( FEATURE_B )
    // Feature B code...
#endif

#if USING( FEATURE_C )
    // Feature C code...
#endif

#if USING( FEATURE_D ) // Compile error since FEATURE_D was never defined
    // Feature D code...
#endif
}

我的问题（我不记得的部分）是如何定义'USING'宏，以便在功能尚未定义为'IN_USE'或'NOT_IN_USE'时出错？如果您忘记包含正确的头文件，可能就是这种情况。

#define USING( feature ) ((feature == IN_USE) ? 1 : ((feature == NOT_IN_USE) ? 0 : COMPILE_ERROR?))

Answer 1

您的示例已经达到了您想要的效果，因为如果未定义#if USING(x)，USING将生成错误消息。您在头文件中需要的只是

#define IN_USE 1
#define NOT_IN_USE 0
#define USING(feature) feature

如果你想确保你只是因为做

之类的事情而得到错误

#if FEATURE

或

#if USING(UNDEFINED_MISPELED_FEETURE)

那么你可以做，比方说，

#define IN_USE == 1
#define NOT_IN_USE == 0
#define USING(feature) 1 feature

但你无法阻止这种误用

#ifdef FEATURE

Answer 2

如果它没有被使用，就不要定义它

#if defined( WIN32 )
    #define FEATURE_A       
    #define FEATURE_B       
#else if defined( OSX )
    #define FEATURE_C      
#else

#endif

然后在你的代码中：

void DoFeatures()
{
#ifdef FEATURE_A
    // Feature A code...
#endif

#ifdef FEATURE_B
    // Feature B code...
#endif

#ifdef FEATURE_C
    // Feature C code...
#endif

#ifdef FEATURE_D // Compile error since FEATURE_D was never defined
    // Feature D code...
#endif
}

Answer 3

你不能只使用另一组#ifdef s？

#if defined(WIN32)
    #define FEATURE_A
    #define FEATURE_B
#elif defined (OSX)
    #define FEATURE_C
#endif

// ...

#if defined(FEATURE_A)
    do_a();
#endif

等

Answer 4

#define IN_USE      1
//#define NOT_IN_USE  _  //Not required


#if defined( WIN32 )
    #define FEATURE_A       IN_USE
    #define FEATURE_B       IN_USE
    #define FEATURE_C       NOT_IN_USE
#elif defined( OSX )
    #define FEATURE_A       NOT_IN_USE
    #define FEATURE_B       NOT_IN_USE
    #define FEATURE_C       IN_USE
#else
    #define FEATURE_A       NOT_IN_USE
    #define FEATURE_B       NOT_IN_USE
    #define FEATURE_C       NOT_IN_USE
#endif

#define USING( feature ) feature

然后你的代码

Answer 5

这样的事情怎么样？

#define IN_USE      1
#define NOT_IN_USE  0

#if defined( WIN32 )
    #define FEATURE_A       IN_USE
    #define FEATURE_B       IN_USE
    #define FEATURE_C       NOT_IN_USE
#elif defined( OSX )
    #define FEATURE_A       NOT_IN_USE
    #define FEATURE_B       NOT_IN_USE
    #define FEATURE_C       IN_USE
#else
    #define FEATURE_A       NOT_IN_USE
    #define FEATURE_B       NOT_IN_USE
    #define FEATURE_C       NOT_IN_USE
#endif

#define USING(f) ((f == IN_USE) ? 1 : (f == NOT_IN_USE) ? 0 : (f))

#include <stdio.h>

void DoFeatures()
{
#if USING( FEATURE_A )
    // Feature A code...
    printf("Feature A\n");
#endif

#if USING( FEATURE_B )
    // Feature B code...
    printf("Feature B\n");
#endif

#if USING( FEATURE_C )
    // Feature C code...
    printf("Feature C\n");
#endif

#if defined( FEATURE_D ) // Compile error since FEATURE_D was never defined
    // Feature D code...
    printf("Feature D\n");
#else
#error FEATURE_D not defined.
#endif
}

int main(int argc, char **argv)
{
    DoFeatures();
    return 0;
}

对于编译错误，我不知道如何将它集成到宏中。如果有人能为我们提供一些启示，将不胜感激。：P

Answer 6

以下作品。它将为FEATURE_D提供编译错误。如果您注释掉FEATURE_D的代码，那么它将执行FEATURE_A和FEATURE_B的代码。代码几乎是不言自明的。您可以将它们放在if块中，而不是检查是否在DoFeatures函数中定义了FEATURE_D或其他内容。这样，编译器将尝试执行代码块。如果是1，则if块中的代码将被执行;在0的情况下，它将不会被执行。如果它从未被定义，那么将得到编译错误。

#include <stdio.h>

#define IN_USE      1
#define NOT_IN_USE  0

#define FEATURE_A       IN_USE
#define FEATURE_B       IN_USE
#define FEATURE_C       NOT_IN_USE


void DoFeatures()
{
    if(FEATURE_A){
        // Feature A code...
        printf("Feature A\n");
    }

    if(FEATURE_B){
        // Feature B code...
        printf("Feature B\n");
    }

    if(FEATURE_C){
        // Feature C code...
        printf("Feature C\n");
    }

    if(FEATURE_D) {// Compile error since FEATURE_D was never defined
        // Feature D code...
        printf("Feature D\n");
    }
}

int main(int argc, char **argv)
{
    DoFeatures();
    return 0;
}

C宏启用和禁用代码功能

6 个答案: