C++ 我可以使用基于范围的 for 循环轻松迭代地图的值吗？
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Can I easily iterate over the values of a map using a range-based for loop?
提问by Blacklight Shining
Is it possible to iterate over all of the values in a std::map using just a foreach?
是否可以仅使用 foreach 迭代 std::map 中的所有值？
This is my current code:
这是我当前的代码：
std::map<float, MyClass*> foo ;
for (map<float, MyClass*>::iterator i = foo.begin() ; i != foo.end() ; i ++ ) {
MyClass *j = i->second ;
j->bar() ;
}
Is there a way I can do this?
有没有办法做到这一点？
for (MyClass* i : /*magic here?*/) {
i->bar() ;
}
采纳答案by Xeo
The magic lies with Boost.Range's map_valuesadaptor:
神奇之处在于Boost.Range 的map_values适配器：
#include <boost/range/adaptor/map.hpp>
for(auto&& i : foo | boost::adaptors::map_values){
i->bar();
}
And it's officially called a "range-based for loop", not a "foreach loop". :)
它被正式称为“基于范围的 for 循环”，而不是“foreach 循环”。:)
回答by Daniel Langr
From C++1z/17, you can use structured bindings:
从C++1z/17 开始，您可以使用结构化绑定：
#include <iostream>
#include <map>
#include <string>
int main() {
std::map<int, std::string> m;
m[1] = "first";
m[2] = "second";
m[3] = "third";
for (const auto & [key, value] : m)
std::cout << value << std::endl;
}
回答by lovaya
std::map<float, MyClass*> foo;
for (const auto& any : foo) {
MyClass *j = any.second;
j->bar();
}
in c++11 (also known as c++0x), you can do this like in C# and Java
在 c++11（也称为 c++0x）中，你可以像在 C# 和 Java 中那样做
