C++ Log File Class
C++ can become very difficult to use especially with large projects where you can't see all the variables. Here's a very simple C++ logging class that can take logs for your software without any effort. This will make you a better programmer as you won't have to rely on debuggers like in Microsoft's Visual Studio.
First you should create a project, with files like log.h and log.cpp. Let's show you the log.h file:
using namespace std;
class Log {
public:
Log(char* filename);
~Log();
void Write(char* logline);
private:
ofstream m_stream;
};
I included fstream for ofstream (which is an output file stream).
The logging class is called Log, it has one private (non-accessible variable by non-class-members) member called m_stream which will be the file stream to write our logs.
I have 3 functions, one constructor called Log, which takes a char pointer input filename, and a destructor ~Log to close our file and avoid memory leaks, and finally a void Write function which will take a logline char pointer.
Here's the log.cpp file:
Log::Log(char* filename) {
m_stream.open(filename);
}
void Log::Write(char* logline){
m_stream << logline << endl;
}
Log::~Log(){
m_stream.close();
}
I included the log.h, then defined the implementation for the 3 functions.
The constructor will open the file delivered by filename on our stream.
The Write function will take a string and write it to the log using << operator, and will add a new line (endl) to the end of each call.
~Log the destructor will close the stream.
This really helps with debugging, so now I'll demonstrate how it can be used in a project. Of course the code can be improved so that you write less code in your main project.
#include <cstdlib>
int main(){
Log *pLog = new Log("errors.log");
pLog->Write("Going into our loop");
for(int i = 0; i < 10; i++){
char c[50];
sprintf(c, "Looped: %d times", i);
pLog->Write(c);
}
return 0;
}
I created a Log class pointer, with the parameter "errors.log" which will be my error logs file.
I call Write to write a line of errors to my log.
If you need to include integers or other variable types, it may be an idea to use sprintf to add the integer i to a char, which you can then write to your log.
Variadic Functions
If you want to avoid using sprintf, and just using Write with va_list, or variadic argument lists:
Using the following modification to Write function, you can create a C++ variadic function. This should allow you to avoid using sprintf every time.
void Log::Write(const char* logline, ...){
va_list argList;
char cbuffer[1024];
va_start(argList, logline);
vsnprintf(cbuffer, 1024, logline, argList);
va_end(argList);
m_stream << cbuffer << endl;
}