How can I write some trace in my log file in C++ - c++

Question

I want to write the date of the execution and the end of execution of a file in my log file.
I can't install anything, just use standard module ( I execute my code in command line with linux ).
I want something like this :
[TRACE] 2014-07-24 14:18:50,2014-07-24 14:18:52
I have this result for the moment :
[TRACE] , Start date of execution : Aug 25 2014 : 10:43:02
End date of execution : Mon Aug 25 10:43:06 2014
here my code :
#include <iostream>
#include <string>
#include <fstream>
#include <ctime>
using namespace std;
void startDateExecution(fstream& file) {
if(fichier)
{
file << "[TRACE]" << " , " << "Start date of execution : " << __DATE__ << " : " << __TIME__ << endl;
}
else
cerr << "Unable to open file" << endl;
}
void endDateExecution(fstream& file) {
time_t result = time(NULL);
file << "End date of execution : " << asctime(localtime(&result)) << endl;
file.close();
}
void displayDate(fstream& file) {
startDateExecution(file);
endDateExecution(file);
}
int main(){
fstream file("trace.log", ios::out | ios::trunc);
displayDate(file);
return 0;
}

Answer 1

You can use log4cpp library. It has lots of other features too. There are sample programs available on the following website.
http://log4cpp.sourceforge.net/
You just need to instantiate the appender based on the needs. I have used RollingFileAppender in my project where I needed the log file to be divided after some threshold (i.e. file size reaches 1MB). Then you need to set the pattern in which you want the logs to be written.
Hope this helps.

Answer 2

As many have commented, __DATE__ and __TIME__ refer to the time of compilation, not execution.
You'll need to retrieve the current time both at the start and at the end of the execution; you'll use the same method, whichever one you use, in both cases.
Here's an example of how you can format time using strftime.
std::string format(time_t when)
{
char timestr[256] = {0};
const char* my_format = "%m/%d/%y # %H:%M:%S";
std::strftime(timestr, sizeof(timestr), my_format, std::localtime(&when));
return timestr;
}
You would use it like this:
int main()
{
time_t start = std::time(NULL);
// Do stuff
time_t end = std::time(NULL);
std::cout << "Start: " << format(start) << std::endl
<< "End: " << format(end) << std::endl;
}
Read the documentation for strftime to learn how to specify your own format.