通过boost lambda占位符访问成员变量 [英] Accessing member variables through boost lambda placeholder

问题描述

我试图使用lambda表达式打印stl地图中所有项目的第二个成员变量

I'm trying to print the second member variable of all items in an stl map using a lambda expression

map<int, int> theMap;
for_each(theMap.begin(), theMap.end(), 
         cout << bind(&pair<int, int>::second, _1) << constant(" "));

但这不是编译。我本质上想取消引用占位符。

but this is not compiling. I essentially want to de-reference the placeholder. Any idea what I'm missing here?

提前感谢！

推荐答案

std :: map 将向其键添加 const 这是为了防止弄乱排序。您的对应为：

std::map will add const to its key; this is to prevent messing up the ordering. Your pair should be:

std::pair<const int, int>

像dirkgently建议，使用 value_type 总是得到正确的类型。使用typedef可以减轻冗长性：

Like dirkgently suggests, use the value_type to always get the correct type. The verbosity is alleviated with a typedef:

typedef std::map<int, int> int_map;

int_map::value_type::second

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