C预处理器宏是否可以包含预处理程序指令？

我想做相同的以下内容:

#define print_max(TYPE) \
#  ifdef TYPE##_MAX \
     printf("%lld\n", TYPE##_MAX); \
#  endif

print_max(INT);

现在#ifdef,就我在函数宏中看到的那样,不允许使用任何嵌套的预处理程序指令.有任何想法吗？

更新:所以看起来这是不可能的.即使是在运行时检查的黑客也无法实现.所以我想我会选择以下内容:

#ifndef BLAH_MAX
#  define BLAH_MAX 0
#endif
# etc... for each type I'm interested in

#define print_max(TYPE) \
    if (TYPE##_MAX) \
       printf("%lld\n", TYPE##_MAX);

print_max(INT);
print_max(BLAH);

Josh Kelley.. 13

该升压预处理器(它支持C和C++,即使升压作为一个整体是一个C++库)库可以用这种任务的帮助.它不是在宏中使用#ifdef(不允许),而是帮助您多次包含文件,每次定义不同的宏,以便文件可以使用#ifdef.

如果保存到max.c,下面的代码应该对文件顶部的MAXES #define中列出的每个单词执行所需的操作.但是,如果任何_MAX值都是浮点数,它将无法工作,因为预处理器无法处理浮点数.

(Boost处理器是一个方便的工具,但它并不简单;你可以决定这种方法是否比复制和粘贴更好.)

#define MAXES (SHRT)(INT)(LONG)(PATH)(DOESNT_EXIST)

#if !BOOST_PP_IS_ITERATING

/* This portion of the file (from here to #else) is the "main" file */

#include 
#include 
#include 

/* Define a function print_maxes that iterates over the bottom portion of this
 * file for each word in MAXES */
#define BOOST_PP_FILENAME_1 "max.c"
#define BOOST_PP_ITERATION_LIMITS (0,BOOST_PP_DEC(BOOST_PP_SEQ_SIZE(MAXES)))
void print_maxes(void) {
#include BOOST_PP_ITERATE()
}

int main(int argc, char *argv[])
{
    print_maxes();
}

#else

/* This portion of the file is evaluated multiple times, with
 * BOOST_PP_ITERATION() resolving to a different number every time */

/* Use BOOST_PP_ITERATION() to look up the current word in MAXES */
#define CURRENT BOOST_PP_SEQ_ELEM(BOOST_PP_ITERATION(), MAXES)
#define CURRENT_MAX BOOST_PP_CAT(CURRENT, _MAX)

#if CURRENT_MAX
printf("The max of " BOOST_PP_STRINGIZE(CURRENT) " is %lld\n", (long long) CURRENT_MAX);
#else
printf("The max of " BOOST_PP_STRINGIZE(CURRENT) " is undefined\n");
#endif

#undef CURRENT
#undef CURRENT_MAX

#endif

Johannes Sch.. 6

我之前尝试过.问题是#已经保留了字符串化宏参数.它不会被解析为预处理器令牌,如#define中的那个.

该升压预处理器(它支持C和C++,即使升压作为一个整体是一个C++库)库可以用这种任务的帮助.它不是在宏中使用#ifdef(不允许),而是帮助您多次包含文件,每次定义不同的宏,以便文件可以使用#ifdef.

如果保存到max.c,下面的代码应该对文件顶部的MAXES #define中列出的每个单词执行所需的操作.但是,如果任何_MAX值都是浮点数,它将无法工作,因为预处理器无法处理浮点数.

(Boost处理器是一个方便的工具,但它并不简单;你可以决定这种方法是否比复制和粘贴更好.)

#define MAXES (SHRT)(INT)(LONG)(PATH)(DOESNT_EXIST)

#if !BOOST_PP_IS_ITERATING

/* This portion of the file (from here to #else) is the "main" file */

#include 
#include 
#include 

/* Define a function print_maxes that iterates over the bottom portion of this
 * file for each word in MAXES */
#define BOOST_PP_FILENAME_1 "max.c"
#define BOOST_PP_ITERATION_LIMITS (0,BOOST_PP_DEC(BOOST_PP_SEQ_SIZE(MAXES)))
void print_maxes(void) {
#include BOOST_PP_ITERATE()
}

int main(int argc, char *argv[])
{
    print_maxes();
}

#else

/* This portion of the file is evaluated multiple times, with
 * BOOST_PP_ITERATION() resolving to a different number every time */

/* Use BOOST_PP_ITERATION() to look up the current word in MAXES */
#define CURRENT BOOST_PP_SEQ_ELEM(BOOST_PP_ITERATION(), MAXES)
#define CURRENT_MAX BOOST_PP_CAT(CURRENT, _MAX)

#if CURRENT_MAX
printf("The max of " BOOST_PP_STRINGIZE(CURRENT) " is %lld\n", (long long) CURRENT_MAX);
#else
printf("The max of " BOOST_PP_STRINGIZE(CURRENT) " is undefined\n");
#endif

#undef CURRENT
#undef CURRENT_MAX

#endif

我之前尝试过.问题是#已经保留了字符串化宏参数.它不会被解析为预处理器令牌,如#define中的那个.