C11中_Generic的语法和用法示例

Question

我听说C11增加了泛型。我用谷歌搜索了一下，看了一些文章，了解到有一个新的关键字( _Generic )等等。但我似乎不能全部掌握。

它是类似于C#中的泛型还是C++中的模板？谁能给我简单解释一下泛型的C11定义，它的语法和一个简单的示例用法示例？

Answer 1

This是一个非常好的介绍。以下是概述：

通用选择是通过一个新关键字实现的：_Generic。其语法类似于类型的简单切换语句：_Generic( 'a', char: 1, int: 2, long: 3, default: 0)的计算结果为2(字符常量在C中为整数)。

基本上，它的工作方式类似于一种switch，其中的标签是根据第一个表达式(上面的'a' )的类型进行测试的类型名称。结果将成为对_Generic()求值的结果。

Answer 2

The best example I have seen启发了以下(可运行的)示例，它为破解的自省解锁了各种奇怪的可能性……

#include <stdio.h>
#include <stddef.h>
#include <stdint.h>

#define typename(x) _Generic((x),        /* Get the name of a type */             \
                                                                                  \
        _Bool: "_Bool",                  unsigned char: "unsigned char",          \
         char: "char",                     signed char: "signed char",            \
    short int: "short int",         unsigned short int: "unsigned short int",     \
          int: "int",                     unsigned int: "unsigned int",           \
     long int: "long int",           unsigned long int: "unsigned long int",      \
long long int: "long long int", unsigned long long int: "unsigned long long int", \
        float: "float",                         double: "double",                 \
  long double: "long double",                   char *: "pointer to char",        \
       void *: "pointer to void",                int *: "pointer to int",         \
      default: "other")

#define fmt "%20s is '%s'\n"
int main() {

  size_t s; ptrdiff_t p; intmax_t i; int ai[3] = {0}; return printf( fmt fmt fmt fmt fmt fmt fmt fmt,

     "size_t", typename(s),               "ptrdiff_t", typename(p),     
   "intmax_t", typename(i),      "character constant", typename('0'),
 "0x7FFFFFFF", typename(0x7FFFFFFF),     "0xFFFFFFFF", typename(0xFFFFFFFF),
"0x7FFFFFFFU", typename(0x7FFFFFFFU),  "array of int", typename(ai));
}

╔═══════════════╗ ═════════════════╣ Amazeballs... ╠═════════════════════════════════════ ╚═══════════════╝ size\_t is 'unsigned long int' ptrdiff\_t is 'long int' intmax\_t is 'long int' character constant is 'int' 0x7FFFFFFF is 'int' 0xFFFFFFFF is 'unsigned int' 0x7FFFFFFFU is 'unsigned int' array of int is 'other'

Answer 3

我使用的是clion 1.2.4，而clion现在不支持c11，所以我在c99中使用了以下代码，而不是_Generic

#include <stdio.h>

int main(int argc, char **argv) {
    char *s;
    if (__builtin_types_compatible_p(__typeof__(s), long)) {
        puts("long");
    } else if (__builtin_types_compatible_p(__typeof__(s), char*)) {
        puts("str");
    }
    return (0);
};