C++ – Why the switch statement cannot be applied on strings

cstringswitch statement

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":
    }
}

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?

Best Answer

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.

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.

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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