How to insert char in middle of text file?

Question

Firstly, I want to insert characters into a text file. I want to print the characters (DAD1) into the middle of the text file (HERE with DA D1) and the

Answer 1

The other answers are suggesting loading the entire file into memory, so I thought I would leave a comment:

If memory is an issue, try the following:

1. Iterate through file to determine its size (do not load into memory).
2. Set file pointer to size/2 and read the latter half of the file into memory.
3. Insert byte(s) at index of size/2.
4. Append latter half of memory after inserted bytes.

Advantages: Can handle a file twice the size of your memory, less copying.

Disadvantage: More iteration