问题:

Is it possible to iterate over all of the values in a std::map using just a foreach?

This is my current code:

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?

for (MyClass* i : /*magic here?*/) {
    i->bar() ;
}

回答1:

The magic lies with Boost.Range's map_values adaptor:

#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". :)

回答2:

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

回答3:

From C++1z/17, you can use structured bindings:

#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;
}