C++ map - expression must be an integral constant

问题:

This question already has an answer here:

• Am I missing anything here in my statement about c++? 5 answers

#include <map>
#include <string>

std::map<std::string, int> foo;
foo["bar"] = 1;

Why do I get the error "expression must be an integral constant expression" in visual studio 12?

I can't work this one out...

回答1:

You need to place the code inside a function.

#include <map>
#include <string>

void xyz()
{
   std::map<std::string, int> foo;
   foo["bar"] = 1;
}

I verified VS 2013 has a problem otherwise, but it works when inside a function. As others have noted, most statements aren't allowed outside of a function.