Pass system date and time as a filename in C++ - c++

Question

I wanted to make an Attendance system which would take system date and time as file name of the file for ex:
this is how normally it is
int main () {
time_t t = time(0); // get time now
struct tm * now = localtime( & t );
cout << (now->tm_year + 1900) << '-'
<< (now->tm_mon + 1) << '-'
<< now->tm_mday
<< endl;
ofstream myfile;
myfile.open ("example.txt");
myfile << "Writing this to a file.\n";
myfile.close();
return 0;
}
but i want system date and time in place of example.txt
i have calculated time by including ctime header file in the program above program is just example .

Answer 1

You can use strftime() function to format time to string,It provides much more formatting options as per your need.
int main (int argc, char *argv[])
{
time_t t = time(0); // get time now
struct tm * now = localtime( & t );
char buffer [80];
strftime (buffer,80,"%Y-%m-%d.",now);
std::ofstream myfile;
myfile.open (buffer);
if(myfile.is_open())
{
std::cout<<"Success"<<std::endl;
}
myfile.close();
return 0;
}

Answer 2

#include <algorithm>
#include <iomanip>
#include <sstream>
std::string GetCurrentTimeForFileName()
{
auto time = std::time(nullptr);
std::stringstream ss;
ss << std::put_time(std::localtime(&time), "%F_%T"); // ISO 8601 without timezone information.
auto s = ss.str();
std::replace(s.begin(), s.end(), ':', '-');
return s;
}
Replace std::localtime* with std::gmtime* if you work together abroad.
Usage e.g.:
#include <filesystem> // C++17
#include <fstream>
#include <string>
namespace fs = std::filesystem;
fs::path AppendTimeToFileName(const fs::path& fileName)
{
return fileName.stem().string() + "_" + GetCurrentTimeForFileName() + fileName.extension().string();
}
int main()
{
std::string fileName = "example.txt";
auto filePath = fs::temp_directory_path() / AppendTimeToFileName(fileName); // e.g. MyPrettyFile_2018-06-09_01-42-00.log
std::ofstream file(filePath, std::ios::app);
file << "Writing this to a file.\n";
}
*See here for a thread-safe alternative of those functions.

Answer 3

You could try using ostringstream to create a date string (as you're doing with cout), then use it's str() member function to retrieve the corresponding date string.

Answer 4

You can use stringstream class for this purpose, for example:
int main (int argc, char *argv[])
{
time_t t = time(0); // get time now
struct tm * now = localtime( & t );
stringstream ss;
ss << (now->tm_year + 1900) << '-'
<< (now->tm_mon + 1) << '-'
<< now->tm_mday
<< endl;
ofstream myfile;
myfile.open (ss.str());
myfile << "Writing this to a file.\n";
myfile.close();
return 0;
return(0);
}