C++: 'set' and 'vector' "undeclared despite #include statements

问题

I am using Netbeans 7.1 on Ubuntu 11.04.

The following call

set< Triangle > V;

gives the error message

error: ‘set’ was not declared in this scope

and the following call

vector< Triangle > ans;

gives the error message

error: ‘vector’ was not declared in this scope

This despite my having

#include <vector>
#include <set>
#include <map>

at the beginning of the C++ file.

At help resolving this would be greatly appreciated.
Peter.

回答1:

you forgot about namespace std :

std::set< Triangle > V; std::vector< Triangle > V;

回答2:

Vectors Sets and map are part of the c++ Standard Library so you need to call vector/set/map with

std::vector< Triangle > ans;

or add

using namespace std;

after the include statements.

回答3:

They live in the std namespace. So, either fully quality the types (std::vector) or use a using statement (using namespace std;).

The latter option pollutes the global namespace. Never do that in a header file (otherwise the entire namespace is imported when you include the header) and only do it in your implementation file if you know that it isn't going to cause any collisions.

#include <vector>

int main(...) {
    vector v;      // no worky
    std::vector v; // ok!
}

来源：https://stackoverflow.com/questions/9243629/c-set-and-vector-undeclared-despite-include-statements