使用std :: string作为std :: map的键 [英] Using an std::string as a key for an std::map

问题描述

我想要一个std :: map（int .NET 4.0）。我们当然知道地图是一棵树，那个字符串没有为我们定义。

错误24错误C2676：二进制'<'：'const std :: string'不定义此运算符或转换为类型可以预先定义的操作符c：\program files\microsoft visual studio 10.0 \vc\include\xfunctional 125 1 FXCMMarketDataServer

所以我把我的google-foo工作，找到这个解决方案：

  struct StringComparerForMap 
 {
 public：
 bool operator（）（const std :: string x，const std :: string y）
 {
 //添加比较逻辑
} 
}; 
 
 ... 
 std :: map< std :: string，CustomObject，StringComparerForMap> MYMAP; 
  

这工作正常了一段时间，现在我遇到了一个我认为是由这个。在STL框架的某个地方，似乎忽略了上述定义，默认为运算符<。

VS2010 .NET 4.0中是否有一种方法来使用字符串作为地图的关键？

我明白，我可以拿这个字符串并写一个函数将其哈希到一个int，但那里的乐趣在哪里？ p>

编辑

我将尽力为大卫做最好的解释。当映射使用比较器结构体时，它在释放中崩溃，并且在调试中失败了调试断言。断言失败的是xtree行1746.

表达式：无效运算符<

|中止| |重试| |忽略|

这是什么让我相信，尽管给了地图一个比较器，但是仍然下降某些路径默认为运算符&作比较。我的代码中导致这个的行是：

  CustomObject o = stringObjectMap [key]; 
  

解决方案

错误24错误C2676 ：binary'<'：'const std :: string'不定义此运算符或转换为预定义运算符可接受的类型c：\program files\microsoft visual studio 10.0\vc\include\ xfunctional 125 1 FXCMMarketDataServer

当您忘记包含< string> 。那个标题肯定定义了这个操作符。

I would like to have an std::map (int .NET 4.0). We of course know that a map is a tree and requires an operator< that string does not define for us.

Error 24 error C2676: binary '<' : 'const std::string' does not define this operator or a conversion to a type acceptable to the predefined operator c:\program files\microsoft visual studio 10.0\vc\include\xfunctional 125 1 FXCMMarketDataServer

So I put my google-foo to work and found this solution:

struct StringComparerForMap
{
public:
    bool operator()(const std::string x, const std::string y)
    {
         // Add compare logic here
    }
};

...
std::map<std::string, CustomObject, StringComparerForMap> myMap;

This worked fine for a while, and now I'm encountering a bug that I believe is due to this. Somewhere deep down in the STL framework it would seem that it ignores the above definition and defaults to operator<.

Is there a way in VS2010 .NET 4.0 to use a string as the key of a map?

I understand that I can take that string and write a function to hash it to an int, but where's the fun in that?

EDIT

I will try and explain this as best I can for David. When the map uses the comparer struct, it crashes in release and fails a debug assertion in debug. The assert that fails is in xtree line 1746.

Expression: invalid operator<

|Abort| |Retry| |Ignore|

That is what leads me to believe that despite giving map a comparer, it still down certain paths defaults to operator< for comparison. The line in my code that causes this is:

CustomObject o = stringObjectMap[key];

解决方案

Error 24 error C2676: binary '<' : 'const std::string' does not define this operator or a conversion to a type acceptable to the predefined operator c:\program files\microsoft visual studio 10.0\vc\include\xfunctional 125 1 FXCMMarketDataServer

That's what VC spits into your face when you forgot to include <string>. That header definitely defines this operator.

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