how to initialize static reference to std::ofstream? - c++

Question

I have a class Cl with public member
static std::ofstream &_rout;
In main file
ofstream out("output.txt");
ofstream& Cl::_rout(out);
But I have a compilation error: illegal definition or redefinition.
How can I correct it?

Answer 1

Try this.
Logger.h
#include <string>
#include <fstream>
#include <iostream>
using namespace std;
class Logger{
public:
static void open( const string & logFile);
static void close();
// write message
static void write( const string & message);
private:
Logger();
ofstream fileStream;
//Logger instance (singleton)
static Logger instance;
};
Logger.cpp
#include "Logger.h"
Logger Logger::instance;
Logger::Logger(){}
void Logger::open( const string& logFile){
instance.fileStream.open(logFile.c_str());
}
void Logger::close(){
instance.fileStream.close();
}
void Logger::write(const string& message){
ostream& stream = instance.fileStream ;
stream << message<< endl;
}
main.cpp
#include "Salida/Logger.h"
int main(){
Logger::open(path);
Logger::write("text");
Logger::close();
return 0;
}

Answer 2

You can only set the reference at the static/global scope
#include<CL.h>
ofstream& Cl::_rout(out);
int main() {
// ...
}
It is not possible to re-set a reference after it was declared (and initialized). You could achieve what you are after by using pointers instead of references:
class Cl {
static std::ofstream* _rout;
};
std::ofstream* CL::_rout = NULL;
int main() {
ofstream out("output.txt");
Cl::_rout = &out;
}
Note that the pointer will be valid only until out goes out of scope. If this is an issue, allocate the memory dynamically:
ofstream* out = new ofstream("output.txt");
Cl::_rout = out;
And don't forget to delete it when you no longer need the object to avoid memory leaks

Answer 3

Well, you could use the following approach:
#include <fstream>
class CI
{
public:
static std::ofstream &_rout;
};
static std::ofstream out("output.txt");
std::ofstream& CI::_rout = out;
int main()
{
}
The problem with this, however, is that the name of the output file is fixed (hard-coded into the program).
I suggest that you use a pointer instead of a reference:
#include <cstddef>
#include <fstream>
class CI
{
public:
static std::ofstream *_rout;
};
std::ofstream* CI::_rout = NULL;
int main()
{
const char *output_file = "output.txt";
std::ofstream out(output_file);
CI::_rout = &out;
}