C++ ostream not creating a new file

Question

This is the WriteAppLog code I used to create a log that app produces but I want to override the previous log OR create a new file with a new name every time.

Can someone help me modify?

void WriteAppLog (const std::string &s) { std::ofstream file ("AppLog.txt", std::ios::app); file << "[" << Helper::DateTime().GetDateTimeString () << "]" << "\n" << s << std::endl << "\n"; file.close(); }

If you don’t want the output appended, don’t use the append flag. But I think you’ll find that you do want to append messages. It is easier to see what was going on after the event if you have all the logged messages. — Jonathan Leffler
– Jonathan Leffler, Commented Oct 14, 2018 at 14:41
You don't need file.close(), the stream closes itself when going out of scope. — skalet
– skalet, Commented Oct 14, 2018 at 14:43
@skalet True, but closing the file manually is the only way to check for errors of the close operation. — zett42
– zett42, Commented Oct 14, 2018 at 16:58

Rabbid76 · Accepted Answer · 2018-10-14 17:18:21Z

The mode flag std::ios::app indicates that the output should be appended to the file. You have to use std::ios::out:

std::ofstream file ("AppLog.txt", std::ios::out);

See std::ofstream

OR create a new file with a new name

If you want to check if a file exists, then you can try to open the file for reading and check by std::ios::good() if this succeeded:

bool exists( const std::string& fileName ) { std::ifstream infile(fileName.c_str()) return infile.good(); }

Dependent on the result you can create a new file with a new name.

Using the exist() function would pose a TOCTOU race condition.

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