我如何检查，如果一个变量是某种类型的C（比较两种类型）？ [英] How do I check if a variable is of a certain type (compare two types) in C?

问题描述

在C（不是C ++ / C＃）我该如何检查，如果一个变量是某种类型的。例如这样的事情：

In C (not C++/C#) how do I check if a variable is of a certain type. For example something like this:

double doubleVar;
if( typeof(doubleVar) == double ) {
    printf("doubleVar is of type double!");
}

或者更一般的：我怎样比较两个类型，以便比较（double1，double2）将evalute真实和比较（INT，双） 将评估假的。此外，我想比较不同的组成结构为好。感谢您的帮助。

Or more general: How do I compare two types so that compare(double1,double2) will evalute true and compare(int,double) will evaluate false. Also I'd like to compare structs of different composition as well. Thanks for any help.

修改：
基本上我有对类型结构a和结构B的变量操作的功能。我想做一件事的结构体一个变量和其他与结构B的变量。由于C不支持重载和无效指针损失的类型信息，我需要检查的类型。顺便说一句。这将是在有的typeof 运营商SENCE，如果你不能比较类型？

Edit: Basically I have a function that operates on variables of type "struct a" and "struct b". I want to do one thing with the "struct a" variables and the other with the "struct b" variables. Since C doesn't support overloading and the void pointer losses its type information I need to check for type. Btw. what would be the sence in having a typeof operator, if you can't compare types?

EDIT2 ：
sizeof运算法似乎是对我来说是切实可行的解决方法解决方案。谢谢你的帮助。我还觉得有点奇怪，因为类型知道编译时，但如果我想象中的机器，我可以看到，为什么信息不会存储在类型方面，而是在字节大小方面的进程。尺寸是除了地址真正相关的唯一的事情。

Edit2: The sizeof-method seems to be a practical workaround solution for me. Thanks for your help. I still find it a bit strange since the types are know at compiletime but if I imagine the processes in the machine I can see, why the information is not stored in terms of types but rather in terms of byte size. Size is the only thing really relevant besides addresses.

推荐答案

获取一个变量的类型是，截至目前，有可能在C11与 _Generic 通用选择。它的工作原理在编译时。

Getting the type of a variable is, as of now, possible in C11 with the _Generic generic selection. It works at compile-time.

该构造结是有点像开关。下面是一个示例（从这个答案）：

The syntaxis is a bit like switch. Here's a sample (from this answer):

#define typename(x) _Generic((x),                                                 \
        _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")

要真正使用它的编译时手动类型检查，你可以定义一个枚举与所有你所期望的类型，像这样：

To actually use it for compile-time manual type checking, you can define an enum with all of the types you expect, something like this:

enum t_typename {
    TYPENAME_BOOL,
    TYPENAME_UNSIGNED_CHAR,
    TYPENAME_CHAR,
    TYPENAME_SIGNED_CHAR,
    TYPENAME_SHORT_INT,
    TYPENAME_UNSIGNED_CHORT_INT,
    TYPENAME_INT,
    /* ... */
    TYPENAME_POINTER_TO_INT,
    TYPENAME_OTHER
};

然后用 _Generic 来匹配类型本枚举：

#define typename(x) _Generic((x),                                                       \
        _Bool: TYPENAME_BOOL,           unsigned char: TYPENAME_UNSIGNED_CHAR,          \
         char: TYPENAME_CHAR,             signed char: TYPENAME_SIGNED_CHAR,            \
    short int: TYPENAME_SHORT_INT, unsigned short int: TYPENAME_UNSIGNED_SHORT_INT,     \
          int: TYPENAME_INT,                     \
    /* ... */                                    \
        int *: TYPENAME_POINTER_TO_INT,          \
      default: TYPENAME_OTHER)

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