C++ cannot name txt file after current sytem time and date - c++

Question

Hi im having issue with this code i have made. It will compile but once i hit enter in the program it says this:
Unhandled exception at 0x008E8641 in Log Test.exe: 0xC0000005: Access violation reading location 0x566D846A.
Here is the code:
#include <iostream>
#include <time.h>
#include <fstream>
using namespace std;
int main() {
cin.get();
time_t Time;
Time = time(0);
string Date = __DATE__;
string LOG = Time + "_" + Date;
ofstream TEST;
TEST.open(LOG);
TEST << "This Text Should Appear Inside Of File.";
TEST.close();
cout << "Log has been Made.";
cin.get();
return 0;
}
I beleive that the problem is the time and how i tried putting it into a string but i dont see what i did doesn't work.

Answer 1

I would think that Time is an integer type so this:
Time + "_"
results in pointer addition so that what gets added to the string is a bad pointer to some location beyond the beginning of "_".
You see string literals like "_" actually resolve to an address (pointer). Adding an integer like Time to it simple makes it point elsewhere in memory.
First you need to convert your Time to a string.
I happen to have this code laying around that may work for you:
std::string get_stamp()
{
time_t t = std::time(0);
char buf[sizeof("YYYY-MM-DD HH-MM-SS")];
return {buf, std::strftime(buf, sizeof(buf), "%F %H-%M-%S", std::localtime(&t))};
}
Note: Using std::localtime is not threas-safe.

Answer 2

If you enabled compiler warnings, it should have screamed at you about this line:
string LOG = Time + "_" + Date;
Here, Time is being converted to a pointer, and you're getting undefined behaviour. For a not completely C++ solution, I recommend this simple approach:
time_t t = time(0);
struct tm ttm;
localtime_r( &t, &ttm );
char timestamp[20]; // actually only need 17 chars plus terminator.
sprintf_s( timestamp, sizeof(timestamp), "%04d-%02d-%02d_%02d%02d%02d",
ttm.tm_year + 1900, ttm.tm_mon + 1, ttm.tm_day, ttm.tm_hour, ttm.tm_min, ttm.tm_sec );
string logfilename = string(timestamp) + ".log";
ofstream logfile( logfilename.c_str() );
Note that localtime_r is not completely portable. On windows, use localtime_s, which unfortunately also reverses the order of the arguments.