重载 std::string operator+ 以打印枚举名称

Question

我有一个枚举

    enum ft_dev_type
    {
        SPI_I2C,
        GPIO
    };

我希望能够构造这样的字符串

std::string s = "enum =" + SPI_I2C; //would contain "enum = SPI_I2C"

为此，我试图重载 + 运算符

    std::string operator+(const ft_dev_type type) const
    {
        switch (type)
        {
            case SPI_I2C: return std::string("SPI_I2C");
            case GPIO: return std::string("GPIO");
        }
    }

但我得到

将 'ft_dev_type' 添加到字符串不会附加到字符串。

如何正确重载 + 运算符？

[编辑] 下面是类

class driver_FT4222
{

public:
    driver_FT4222() {}

    enum ft_dev_type
    {
        SPI_I2C,
        GPIO
    };

    std::string operator+(const ft_dev_type type) const //this line is probably wrong
    {
        switch (type)
        {
            case SPI_I2C: return std::string("SPI_I2C");
            case GPIO: return std::string("GPIO");
        }
    }

    void doSomething()
    {
        ...
        std::string s = "enum =" + SPI_I2C; //would contain "enum = SPI_I2C"
        std::cout <<s;
        ...
    }
}

Answer 1

看来您想要免费功能：

std::string operator+(const char* s, const ft_dev_type type)
{
    switch (type)
    {
        case SPI_I2C: return s + std::string("SPI_I2C");
        case GPIO: return s + std::string("GPIO");
    }
    throw std::runtime_error("Invalid enum value");
}

（和类似的std::string...）

但更好的 IMO 有一个 to_string

std::string to_string(const ft_dev_type type)
{
    switch (type)
    {
        case SPI_I2C: return std::string("SPI_I2C");
        case GPIO: return std::string("GPIO");
    }
    throw std::runtime_error("Invalid enum value");
}

具有

std::string s = "enum =" + to_string(SPI_I2C);