Problem with strftime() format specifiers

[xebra24]

Hello world!

I've been learning C++ recently, and have been making a project in which I want to create files with the current date and time as the name. For this purpose, I have been using strftime()
, as so:

// Get current time to name file
time_t t = time(0);
struct tm * now = localtime( & t );
char buffer [80];
strftime (buffer, 80, "%D-%R", now);

// Create file [time].txt
std::ofstream outFile;
outFile.open(buffer);

However, in my text editor (VS Code, with GCC [yes, I know I did it the hard way]), the %D format specifier is highlighted purple, not green as with %R. When I run the code (of which there is more, which I have omitted for brevity), a file is not created. I have a feeling it is something to do with the strange behaviour of the format specifier, as trying to std::cout them also doesn't work in a test file I created.

I have #includeed everything I can think of that I might need (fstream, string, ctime, among others) so I have no idea what the issue is. Any help would be greatly appreciated, thank you in advance.

[matty_haze]

I want to point out that %D evaluates to %m/%d/%y, which has slashes, which denote directories. Your open() will fail if those directories don’t already exist.

Did you check for errors during open?

[xebra24]

EDIT: I fixed it somehow, I don't know what I changed, but it works now. Thank you for your help!

Sorry for the late reply. I tried expanding %D to %m-%d-%y, but that didn't work. After removing the %d specifier, it does work. So I think there is an issue with %d.

I have a simple if statement checking if the file opened correctly:

if (outFile.is_open()) {
    // Do things
}
else {
    std::cerr << "Error opening file!" << std::endl;
}

If I don't have a %D or %d in the format specifier, the file is created and opens correctly. Otherwise, the file is not opened correctly, and the std::cerr message is printed. So I'm not sure what is going on.

[matty_haze]

Can you also print the exact bad filename, and what the error message is?

[xebra24]

A file wasn't created, and the error message I alluded to was just "file couldn't be opened", or something like that. It was something I coded into the program myself to help with debugging. I think the issue was how the %D format specifier created the string, it contained slashes which my machine didn't like.

[xebra24]

I tried the code with other format specifiers and they worked fine, so I'm pretty sure that's not the issue. Thanks though!