overwriting a specific line on a text file?

Question

how do I go about overwriting a specific line on a text file in c?. I have values in multiple variables that need to be written onto the file.

Answer 1

This only works when the new line has the same size as the old one:

• Open the file in the mode a+
• fseek() to the start of the file
• Before reading the next line, use ftell() to note the start of the line
• Read the line
• If it's the line you want, fseek() again with the result from ftell() and use fwrite() to overwrite it.

If the length of the line changes, you must copy the file.