why is string not declared in scope

问题

I have the following code:

#include <string>
#include <boost/thread/tss.hpp>

static boost::thread_specific_ptr<string> _tssThreadNameSptr;

I get the following error

g++ -c -I$BOOST_PATH tssNaming.h

tssNaming.h:7: error: 'string' was not declared in this scope

But I am including string in my #include.

回答1:

You have to use std::string since it's in the std namespace.

回答2:

string is in the std namespace. You have the following options:

• Write using namespace std; after the include and enable all the std names: then you can write only string on your program.
• Write using std::string after the include to enable std::string: then you can write only string on your program.
• Use std::string instead of string

回答3:

I find that including:

using namespace std;

To your C++ code saves a lot of time in debugging especially in situations like yours where std:: string is required and also it will help in keeping your code clean.

With this in mind, your code should be:

#include <string>
using namespace std;
#include <boost/thread/tss.hpp>

static boost::thread_specific_ptr<string> _tssThreadNameSptr;

来源：https://stackoverflow.com/questions/12230156/why-is-string-not-declared-in-scope