Possible Duplicate:
C++ static constant string (class member)
static const C++ class member initialized gives a duplicate symbol error when linking
My experience with C++ pre-dated the addition of the string class, so I'm starting over in some ways.
I'm defining my header file for my class and want to create a static constant for a url. I'm attempting this by doing as follows:
#include <string>
class MainController{
private:
static const std::string SOME_URL;
}
const std::string MainController::SOME_URL = "www.google.com";
But this give me a duplicate definition during link.
How can I accomplish this?
Move the
const std::string MainController::SOME_URL = "www.google.com";
to a cpp file. If you have it in a header, then every .cpp that includes it will have a copy and you will get the duplicate symbol error during the link.
You need to put the line
const std::string MainController::SOME_URL = "www.google.com";
in the cpp file, not the header, because of the one-definition rule. And the fact that you cannot directly initialize it in the class is because std::string
is not an integral type (like int).
Alternatively, depending on your use case, you might consider not making a static member but using an anonymous namespace instead. See this post for pro/cons.
Define the class in the header file:
//file.h
class MainController{
private:
static const std::string SOME_URL;
}
And then, in source file:
//file.cpp
#include "file.h"
const std::string MainController::SOME_URL = "www.google.com";
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