CODEWITHSUNDEEP
c++cfile
Cenoc
Cenoc

Reputation: 11672

Clearing Contents of a File in C++ knowing only the FILE *

Is it possible to clear the contents (ie. set EOF to the beginning/reset the file) in C++ knowing just the FILE*? I'm writing to a temp file with wb+ access and wish to sometimes clear it and truncate it without adding the calls to fclose and fopen. I dont think it's possible... but if not, why not?

Thanks in advance!

Upvotes: 2

Views: 612

Answers (3)

M3t0r
M3t0r

Reputation: 182

#include <cstdio>

freopen(null, "w", filePtr);

see http://www.cplusplus.com/reference/clibrary/cstdio/freopen/ for more. espacialy the description for the parameter filename.

Upvotes: -1

Jonathan Leffler
Jonathan Leffler

Reputation: 753805

It will depend on your platform. The POSIX standard provides ftruncate(), which requires a file descriptor, not a FILE pointer, but it also provides fileno() to get the file descriptor from the FILE pointer.

The analogous facilities will be available in Windows environments - but under different names.

Upvotes: 7

Mark B
Mark B

Reputation: 96241

I don't believe this can be done using just the FILE*. You can always write null data through the end of the file but that won't truncate it.

Alternately if you have access to the filename (I can't tell from the question) you could use freopen which hides the close/open/truncate into a single function call.

Upvotes: 0

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