c - C11中_Generic的语法和示例用法

Question

我听说 C11 添加了泛型。我用谷歌搜索了一下，看了一些文章，知道有一个新的关键字（_Generic）等等。但我似乎无法掌握这一切。

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

Answer 1

我见过的最好的例子启发了下面的（可运行的）例子，它为破解内省提供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 2

这是一个很好的介绍。这是概述：

通用选择是使用新关键字实现的：_Generic。语法类似于简单的类型 switch 语句：_Generic( 'a', char: 1, int: 2, long: 3, default: 0) 计算结果为 2（字符常量在 C 中是整数）。

基本上它的工作原理类似于一种，其中标签是针对第一个表达式（如上）switch的类型进行测试的类型名称。'a'结果成为评估的结果_Generic()。

Answer 3

我用的是 clion 1.2.4，现在 clion 不支持 c11，所以我在 c99 中使用下面的代码，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);
};