I am facing problem while overwriting a file at a particular position in C++. I have opened my file using ios::app|ios::binary. Then I seek to that position which I want to overwrite. But instead of overwriting it, I append from the end of the file. Any suggestions?
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nikolas
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user2764874
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8What do you think `ios::app` does? – Jesse Good Sep 10 '13 at 12:45
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2remove the ios::app option? – Theolodis Sep 10 '13 at 12:46
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1About `ios_base::app` (`§27.5.3.1.4`): `seek to end before each write` – Marcin Łoś Sep 10 '13 at 12:46
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if remove it then it will overwrite whole file. – user2764874 Sep 10 '13 at 12:53
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1http://stackoverflow.com/questions/6427698/write-to-the-middle-of-an-existing-binary-file-c – doctorlove Sep 10 '13 at 12:56
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You need to specify ios::in as well as ios::out. It overwrites if you have only ios::out (default in ofstream). As stated ios::app means data is written to the end of the file, which is not what you want.
Mats Petersson
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You can open your file with ios::in|ios::out|ios::binary. After that you should use seekp() to seek to the desired position of the file before the write.
Diego Giagio
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1Using only `ios::out` will empty the file, you need `ios::in` to prevent the file from being emptied (or `ios::app` if you want to write only to the end. – Mats Petersson Sep 10 '13 at 13:00