无法在 C++ 中定义 ++ 运算符，这里有什么问题?

2022-01-19 00:00:00 enums operator-overloading switch-statement c++ c++11

我正在研究 Bjarne Stroustrup 的《C++ 编程语言》，但我被困在其中一个示例上.这是代码，除了空格差异和注释之外，我的代码与书中的代码相同(第 51 页).

I'm working through Bjarne Stroustrup's The C++ Programming Language and I'm stuck on one of the examples. Here's the code, and aside from whitespace differences and comments my code is identical to what's in the book (p.51).

enum class Traffic_light { green, yellow, red};
int main(int argc, const char * argv[])
{
    Traffic_light light = Traffic_light::red;
//    DEFINING OPERATORS FOR ENUM CLASSES
//    enum classes don't have all the operators, must define them manually.
    Traffic_light& operator++(Traffic_light& t) {
        switch (t) {
            case Traffic_light::green:
                return t = Traffic_light::yellow;
            case Traffic_light::yellow:
                return t = Traffic_light::red;
            case Traffic_light::red:
                return t = Traffic_light::green;
        }
    }

    return 0;
}

然而，当我在 Mac OS X 10.9 上使用 clang++ -std=c++11 -stdlib=libc++ -Weverything main.cpp 编译它时，出现以下错误:

Yet when I compile it with clang++ -std=c++11 -stdlib=libc++ -Weverything main.cpp on Mac OS X 10.9 I get the following errors:

main.cpp:24:9: error: expected expression
        switch (t) {
        ^
main.cpp:32:6: error: expected ';' at end of declaration
    }
     ^
     ;

真正的障碍是 expected expression 错误，但 expected ; 也是有问题的.我做了什么?

The real baffeler is the expected expression error, but the expected ; is problematic as well. What have I done?

推荐答案

Traffic_light&operator++(Traffic_light& t) 是一个名为 operator++ 的函数.每个功能都应在任何其他功能之外定义.所以把操作符的定义放在main之前.

Traffic_light& operator++(Traffic_light& t) is a function with name operator ++. Each function shall be defined outside any other function. So place the definition of the operator before main.

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