File edition

[hazardpeter]

Hello, I have been trying to open a file in append mode and write something in a determined position of the file, I have been trying to do it like this:

file.open("file.html", std::ios::out | std::ios::app);//Opens the file in output mode and append mode
file.seekp(23, std::ios::end);//goes to 23 bytes(I think) before the end of file
file << "something" << std::endl;//Writes that something

file.open("file.html", std::ios::out | std::ios::app);//Opens the file in output mode and append mode
file.seekp(23, std::ios::end);//goes to 23 bytes(I think) before the end of file
file << "something" << std::endl;//Writes that something

To copy to clipboard, switch view to plain text mode 

However even with the seekp function what i write always end's up at the end of the file. I would like to know how can I avoid that from happening.

Thanks for now.

[caduel]

that is the intended behaviour if you open the file for appending.

try

file.open("file.html", std::ios::out); //Opens the file in output mode
file.seekp(-23, std::ios::end); //goes to 23 bytes [I]before[/I] the end of file
file << "something" << std::endl;//Writes that something

file.open("file.html", std::ios::out); //Opens the file in output mode
file.seekp(-23, std::ios::end); //goes to 23 bytes [I]before[/I] the end of file
file << "something" << std::endl;//Writes that something

To copy to clipboard, switch view to plain text mode 

note, however, that opening a file in ascii mode and writing out a string as done above usually does not make sense with byte counting and going to 23 bytes before the end...

[hazardpeter]

note, however, that opening a file in ascii mode and writing out a string as done above usually does not make sense with byte counting and going to 23 bytes before the end...

Hum, I will keep that in mind. And thanks for the answer it was really helpful for now.

Edit: unfortunately it didn't work. I think when we open a file in append mode every think just goes to the end of the file and the seekp and seekg don't work. Can I open a file and add something there in a determined position without erasing the rest of of the file???

[caduel]

when you open a file in append mode, you can seek and *read* at different positions. all written data is, however, appended (at the end):

From the manpage of "open" (and I guess we can assume that std::ios::app will behave the same):

APPEND Set the file pointer to the end of the file prior to each write.

When you write data at any position (but the end), the data present at that position will be overwritten. there is no "insert 10 bytes here" mode. You would have to do that yourself.

Finally: "didn't work"... you did notice that in my code snippet the std::ios:app was missing?

[hazardpeter]

(...)
Finally: "didn't work"... you did notice that in my code snippet the std::ios:app was missing?

Lol, sorry I didn't notice that. But Thanks again for everything!