Question

How do I edit a specific line of a text file in C++? Let’s say I want to open a file and change the focus or pointer or whatever its called to line 17 column 20. That way I can edit text after line 17, column 20.

I tried this, but it didnt work.

ofstream txtFile("textFile.txt");
fseek(txtFile, 17, 20);
txtFile << "New stuff to enter at this point (overwrites old not insert)";

How do I do this?

Answer 1

fseek is not seeking counting lines, but rather bytes. What you instruct the program is not to position the pointer at column 20 of 17th line, but rather at the 17 + 20 = 37th byte of the file.

The first parameter of the function is the origin, i.e. the count of bytes from the origin from which you count, and the second – how many more you offset.

See the reference of fseek.

I am not aware of any library that can do byte positioning in respect of lines and columns in C++. You will probably need to use a higher level function and parse lines one by one (e.g. using getline if you are after C++ solution).