Can we reduce size of existing file?

Question

I want to know whether size of text or binary file can be reduced without creating temporary file. So that we can delete the data present at very end of file.

If yes then how. If no then why.

Yes, it is possible to *truncate* a file to a given size. – Jesper Juhl Jul 29 '18 at 09:39 — Jesper Juhl, Jul 29 '18 at 09:39
LOL How was this question "unclear"? – Galik Jul 29 '18 at 11:28 — Galik, Jul 29 '18 at 11:28
Duplicate of https://stackoverflow.com/questions/873454 – Tom Zych Jul 30 '18 at 00:10 — Tom Zych, Jul 30 '18 at 00:10

score 7 · Accepted Answer · answered Jul 29 '18 at 09:47

7

Yes, you can reduce file size using truncate() or ftruncate() functions that are available on POSIX systems.

For Windows, use SetFilePointer to set the current position to desired file size, then call SetEndOfFile to actually truncate it.

answered Jul 29 '18 at 09:47

mvp

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You could also mention the new (standard) *filesystem* option for `C++17`: https://en.cppreference.com/w/cpp/filesystem/resize_file – Galik Jul 29 '18 at 10:03
Thanks a lot, it saved too many calls to file io – Santosh Kale Jul 29 '18 at 12:40

score 2 · Answer 2 · answered Jul 29 '18 at 10:28

2

You can use the resize_file() function from the <filesystem> addition to the Standard Library in C++17:

#include <filesystem>
namespace fs = std::filesystem;

// ...

fs::resize_file(p, 1024); // resize to 1024 bytes

answered Jul 29 '18 at 10:28

Galik

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Will use it future. Currently I'm using older standard. – Santosh Kale Jul 29 '18 at 12:45

Can we reduce size of existing file?

2 Answers2