Simple Logger in C++ with log level - c++

Question

After a long time I started doing some C++ development again. Right now I'm struggling with my logging class. It's already working quite nicely, but I want to introduce some log levels. To be honest, I'm not quite sure how to continue in the right way.
My logger works with five simple macros:
#define PLUGINLOG_INIT(path, fileName) logInstance.initialise(path, fileName);
#define LOG_ERROR (logInstance << logInstance.prefix(error))
#define LOG_WARN (logInstance << logInstance.prefix(warn))
#define LOG_INFO (logInstance << logInstance.prefix(info))
#define LOG_DEBUG (logInstance << logInstance.prefix(debug))
The first one opens the file stream and the other four write log entries into the file. It's a rather simple approach. The prefix methods writes a datetime stamp and the log level as text:
2021-05.26 12:07:23 WARN File not found!
For the log level, I created an enum and store the current log level in my class. My questions is however, how can I avoid logging if the log level is set lower?
Example:
LogLevel in class = warn
When I log an info entry, I'd put the following line into my source code:
LOG_INFO << "My info log entry" << std::endl;
Since the LogLevel is set to warning, this info entry should not be logged. I could try putting an if statement into the LOG_INFO macro, but I would rather avoid complicated macros. Is there a better way to achieve what I need?
Many thanks,
Marco
Complete header file of my logger:
#ifndef PLUGINLOGGER_H_
#define PLUGINLOGGER_H_
// Standard
#include <fstream>
#include <iostream>
#include <memory>
#include <string>
#include <string_view>
// Forward declarations
class PluginLogger;
extern PluginLogger logInstance;
// Enumerations
enum LogLevel {
error = 0,
warn = 1,
info = 2,
debug = 3
};
// Macros
#define PLUGINLOG_INIT(path, fileName) logInstance.initialise(path, fileName);
#define LOG_ERROR (logInstance << logInstance.prefix(error))
#define LOG_WARN (logInstance << logInstance.prefix(warn))
#define LOG_INFO (logInstance << logInstance.prefix(info))
#define LOG_DEBUG (logInstance << logInstance.prefix(debug))
class PluginLogger {
public:
PluginLogger();
void initialise(std::string_view path, std::string_view fileName);
void close();
template<typename T> PluginLogger& operator<<(T t);
// to enable std::endl
PluginLogger& operator<<(std::ostream& (*fun) (std::ostream&));
std::string prefix(const LogLevel logLevel);
private:
std::string m_fileName;
std::ofstream m_stream;
LogLevel m_logLevel;
};
template<typename T> inline PluginLogger& PluginLogger::operator<<(T t) {
if (m_stream.is_open())
m_stream << t;
return* this;
}
inline PluginLogger& PluginLogger::operator<<(std::ostream& (*fun)( std::ostream&)) {
if (m_stream.is_open())
m_stream << std::endl;
return* this;
}
#endif // PLUGINLOGGER_H_
Complete source file of my logger:
#include <chrono>
#include "PluginLogger.h"
PluginLogger logInstance;
PluginLogger::PluginLogger() {
m_fileName = "";
m_logLevel = error;
}
void PluginLogger::initialise(std::string_view path, std::string_view fileName) {
if (!path.empty() && !fileName.empty()) {
m_fileName = std::string(path) + std::string(fileName) + "_log.txt";
m_stream.open(m_fileName);
unsigned char bom[] = { 0xEF,0xBB,0xBF };
m_stream.write((char*)bom, sizeof(bom));
}
}
void PluginLogger::close() {
if (m_stream.is_open())
m_stream.close();
}
std::string PluginLogger::prefix(const LogLevel logLevel) {
// add a date time string
std::time_t now = std::chrono::system_clock::to_time_t(std::chrono::system_clock::now());
std::string dateTimeStr(25, '\0');
std::strftime(&dateTimeStr[0], dateTimeStr.size(), "%Y-%m-%d %H:%M:%S", std::localtime(&now));
// add log level
std::string logLevelText;
switch (logLevel) {
case error:
logLevelText = " ERROR ";
break;
case warn:
logLevelText = " WARN ";
break;
case info:
logLevelText = " INFO ";
break;
case debug:
logLevelText = " DEBUG ";
break;
}
return dateTimeStr + logLevelText;
}