Question

Using PHP, it’s possible to read off the contents of a file using fopen and fgets. Each time fgets is called, it returns the next line in the file.

How does fgets know what line to read? In other words, how does it know that it last read line 5, so it should return the contents of line 6 this time? Is there a way for me to access that line-number data?

(I know it’s possible to do something similar by reading the entire contents of the file into an array with file, but I’d like to accomplish this with fopen.)

Answer 1

There is a “position” kept in memory for each file that is opened ; it is automatically updated each time you are reading a line/character/whatever from the file.

You can get this position with ftell, and modify it with fseek :

ftell — Returns the current position
of the file read/write pointer

fseek — Seeks on a file pointer

You can also use rewind to… rewind… the position of that pointer.

This is not getting you a position as a line number, but closer to a position as a character number (actually, you are getting the position as a number of bytes from the beginning of the file) ; when you have that, reading a line is just a metter of reading characters until yu hit an end of line character.

BTW : as far as I remember, these functions are coming from the C language — PHP itself being written in C 😉