Question

I’m trying to do this:

#pragma once
#include <fstream>
#include <string>

static std::ofstream ErrorLog;

void InitErrorLog(std::string FileName) {
    ErrorLog.open(FileName);
}

but am getting a “One or more multiply defined symbols found” error when #include-ing in multiple CPP files. What is the STL doing (to provide cout, cin, cerr, etc. — this approach originates as an alternative to redirecting cerr) that I’m not?

Answer 1

You’re breaking the one definition rule. You need to make the method inline.

inline void InitErrorLog(std::string FileName) {
    ErrorLog.open(FileName);
}

Also, note that by declaring your variable static, you’ll have a copy per translation unit – i.e. it’s not a global. To make it global, you need to declare it extern in the header and define it in a single implementation file.