Question

我正在尝试std :: map，使用枚举类和std :: string但是我收到了一些错误。我正在使用gcc 4.4.7和-std = c ++ 0x（这是固定的）

在.h档案：

enum class state_t{
    unknown,
    off,
    on,
    fault
};

typedef std::map<state_t,std::string> statemap_t;

在.cpp文件：

statemap_t state={
   {state_t::unknown,"unknown"}
   {state_t::off,"off"}
   {state_t::on,"on"}
   {state_t::fault,"fault"}
}

允许状态转换的方法如下：

Foo::allowStateChange(const state_t localState, const state_t globalState, const state_t newState){
    //Some code to verify if the state transition is allowed.
    std::cout << "Device Local State:" << state.find(localState)->second << "Device Global State:" << state.find(globalState)->second << "Device New State:" << state.find(newState)->second << std::endl;
}

在进行计算时，我会收到下一个错误：错误：类型的无效操作数＆＃39; state_t＆＃39;和＆＃39; state_t＆＃39;到二元＆＃39;运算符＆lt;＆＃39;

如果我将enum class state_t更改为enum state_t则可行。有没有办法在地图中找到枚举类？

提前致谢。

Answer 1

以下代码工作正常（在Visual Studio 2015（v140）上;在您的情况下使用哪个编译器？）：

#include <string>
#include <iostream>
#include <map>

using namespace std;

enum class state_t {
    unknown,
    off,
    on,
    fault
};

typedef std::map<state_t, std::string> statemap_t;

statemap_t state = {
    { state_t::unknown,"unknown" },
    { state_t::off,"off"},
    { state_t::on,"on"},
    { state_t::fault,"fault"}
};

void allowStateChange(const state_t localState, const state_t globalState,     const state_t newState) {
    //Some code to verify if the state transition is allowed.
    std::cout 
        << "Device Local State:" 
        << state.find(localState)->second 
        << ", Device Global State:" 
        << state.find(globalState)->second 
        << ", Device New State:" 
        << state.find(newState)->second 
        << std::endl;
}

int main()
{
    allowStateChange(state_t::on, state_t::off, state_t::fault);
    return 0;
}

BWT，state_t中有一个拼写错误的“unkmown”。

Answer 2

我假设您使用的GCC编译器版本不支持与枚举类关联的所有基础结构。因此，您需要自己实现缺少的运算符，如下所示：

inline bool operator <(const state_t left, const state_t right)
{
    return static_cast<int>(left) < static_cast<int>(right);
}

inline bool operator >(const state_t left, const state_t right)
{
    return static_cast<int>(left) > static_cast<int>(right);
}

在C ++ 11中，这些功能可能是通过模板专门化来实现的，对static_cast使用std :: underlying_type并将限定词专门与枚举类绑定，其中某些可能在-std = c ++ 0x下不可用特定的编译器版本

如何std :: map <enum class，=“”std :: string =“”>？

2 个答案: