ofstream writes hex instead of char* - c++

Question

I try to write a simple Logger but the ofstream writes hex instead of the characters to the file.
Definition:
#pragma once
#include <iostream>
#include <fstream>
#include <string>
#define LOG Logger::getInstance()
class Logger
{
public:
static Logger m_instance;
static Logger &getInstance()
{
if (m_logfile == nullptr)
{
m_logfile = new std::ofstream(m_logfile_string.c_str(),
std::ofstream::out | std::ofstream::app);
}
return m_instance;
}
Logger &operator<<(const std::string &c);
Logger &operator<<(const char c[]);
private:
static std::ofstream *m_logfile;
static std::string m_logfile_string;
Logger() {};
Logger(const Logger &) = delete;
Logger(Logger &&other) = delete;
Logger &operator=(const Logger &other) = delete;
Logger &operator=(Logger &&other) = delete;
~Logger()
{
if (m_logfile != nullptr)
m_logfile->close();
};
std::string currentDateTime() const;
};
Impl.
#include "Logger.h"
#include <iostream>
#include <ctime>
Logger Logger::m_instance;
std::ofstream *Logger::m_logfile = nullptr;
std::string Logger::m_logfile_string = "log.txt";
Logger &Logger::operator<<(const std::string &c)
{
this->operator<<(c.c_str());
return *this;
}
Logger &Logger::operator<<(const char c[])
{
std::cout << currentDateTime() << " - "
<< c << std::endl;
m_logfile->operator<<(c);
return *this;
}
// Get current date/time, format is YYYY-MM-DD.HH:mm:ss
std::string Logger::currentDateTime() const
{
auto now = time(nullptr);
struct tm tstruct;
char buf[80];
tstruct = *localtime(&now);
strftime(buf, sizeof(buf), "%Y-%m-%d.%X", &tstruct);
return buf;
}
Usage:
#include "Logger.h"
void main()
{
LOG << "started"; // Logger::getInstance() << "started";
}
Outcome:
00007FF696EF3C00 in the log.txt The console output is right.
Whats going wrong here?

Answer 1

You use member function of iostream:
m_logfile->operator<<(c);
There is no member function operator<<(char* c), but there is operator<<(void* p), so pointer is implicitly converted. See documentation on ostream.
Operators for char* are not class member functions:
ostream& operator<< (ostream& os, const char* s);
See here: operator<< (ostream)
So you need this code:
operator<<(*m_logfile, c);
Or much more cleaner:
(*m_logfile) << c;
Test example:
#include <iostream>
int main() {
std::cout.operator<<("test");
operator<<(std::cout, "test");
std::cout << "test";
}
Prints 0x400944testtest.

Answer 2

If you use
(*m_logfile)<<c;
instead of
m_logfile->operator<<(c);
It will work.
Reason:
Your syntax calls the member function ostream::operator<<() which is not defined for char* nor for string. It's only defined for void* which always displays address in hex.
The classic syntax calls here the non member function ostream std::operator<<(...) which has overloads for string and char*