Write to File's Last 32 Characters

Question

I want to write an info to binary file's last 32 characters. But when i call my writeInfo function, it deletes the whole content. I can read the data before i write, but after i write with this function, it deletes the whole content, instead of writing.

void Info::writeInfo(char *filedestination)
{
ofstream test;
test.open(filedestination, ios::binary); 
test.seekp(-32, ios::end); // not sure about seekp
test.write(info, 31);
test.close();
}

Hope you can help, thank you

score 2 · Accepted Answer · answered Mar 17 '13 at 18:50

2

You have to open the file in read-write mode to prevent the call to open from truncating it:

test.open(filedestination, ios::binary | ios::in | ios::out);

answered Mar 17 '13 at 18:50

Joni

108,737
14
143
193

score 0 · Answer 2 · answered Mar 17 '13 at 18:44

0

http://www.cplusplus.com/reference/cstdio/fseek/

try using fseek(). link above is documentation

answered Mar 17 '13 at 18:44

sublime.Hat

51
10

That is the C equivalent of `seekp`, which he is already using. Also mixing C and C++ is a bad idea. – loganfsmyth Mar 17 '13 at 18:54

Write to File's Last 32 Characters

2 Answers2