增加迭代器标准映射 [英] Increment an iterator standard map

问题描述

ALL，

std::map<int, std::string> addressee;
std::map<int, std::string>::iterator it1, it2;

for( it1 = addressee.begin(); it1 != addressee().end(); it1++ )
{
    bool found = false;
    for( it2 = it1 + 1; it2 != addressee.end() && !found; it2++ )
    {
       if( it1->second == it1->second )
       {
           printf( "Multiple occurences of addressees found" );
           found = true;
       }
    }
}

gcc吐出错误：不匹配运算符+。

gcc spits out an error: no match for operator+.

此代码是我正在尝试做的简化版本。我想我可以使用std :: advance（），但它似乎只是浪费了函数调用。

This code is a simplified version of what I'm trying to do right now. I guess I can use std::advance(), but it seems it just going to be a waste of the function call.

有更好的解决方法吗？

Is there a better fix for that?

推荐答案

std :: map 没有随机访问迭代器，只有双向迭代器，因此没有 + n 操作。相反，请使用 std :: next ：

std::map does not have random access iterators, only bidirectional iterators, so there's no + n operation. Instead, use std::next:

#include <iterator>
#include <map>

// ...

for (auto it1 = addressee.begin(), e = addressee.end(); it1 != e; ++it1)
{
    for (auto it2 = std::next(it1); it2 != e; ++it2)
    {
        if (it1->second == it2->second)
        {
            // ...
            break;
        }
    }
}

事实上，你应该总是的使用的std ::接下来，因为它知道该迭代器类别的说法有和计算什么是最有效的方式接下来的迭代器。这样，您就不必关心您正在使用的特定容器。

In fact, you should always use std::next, since it knows which iterator category its argument has and what the most efficient way to compute the next iterator is. That way, you don't have to care about the specific container you happen to be using.

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