为什么 switch 语句不能应用于字符串? [英] Why the switch statement cannot be applied on strings?

问题描述

编译下面的代码，得到类型非法的错误.

Compiling the following code and got the error of type illegal.

int main()
{
    // Compilation error - switch expression of type illegal
    switch(std::string("raj"))
    {
    case"sda":
    }
}

您不能在 switch 或 case 中使用字符串.为什么?是否有任何解决方案可以很好地支持类似于打开字符串的逻辑?

You cannot use string in either switch or case. Why? Is there any solution that works nicely to support logic similar to switch on strings?

推荐答案

原因与类型系统有关.C/C++ 并不真正支持字符串作为一种类型.它确实支持常量字符数组的想法，但它并没有真正完全理解字符串的概念.

The reason why has to do with the type system. C/C++ doesn't really support strings as a type. It does support the idea of a constant char array but it doesn't really fully understand the notion of a string.

为了生成 switch 语句的代码，编译器必须理解两个值相等的含义.对于整数和枚举之类的项目，这是一个微不足道的比较.但是编译器应该如何比较 2 个字符串值呢?区分大小写、不敏感、文化意识等......如果不完全了解字符串，则无法准确回答.

In order to generate the code for a switch statement the compiler must understand what it means for two values to be equal. For items like ints and enums, this is a trivial bit comparison. But how should the compiler compare 2 string values? Case sensitive, insensitive, culture aware, etc ... Without a full awareness of a string this cannot be accurately answered.

此外，C/C++ switch 语句通常生成为分支表.为字符串样式开关生成分支表并不容易.

Additionally, C/C++ switch statements are typically generated as branch tables. It's not nearly as easy to generate a branch table for a string style switch.

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