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

编译以下代码，并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":
    }
}

在任何一个中都不能使用字符串开关或情况。为什么？有什么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

与类型有关的原因系统。 C / C ++并不真正支持将字符串作为一种类型。它确实支持常量char数组的概念，但是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，编译器必须了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？区分大小写，不区分大小写，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 ++转换语句通常生成为分支表。为字符串样式开关生成分支表几乎不那么容易。

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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