Read a file backwards line by line using fseek

Question

How do I read a file backwards line by line using fseek?

code can be helpful. must be cross platform and pure php.

many thanks in advance

regards

Answer 1

Reading the entire file into an array and reversing is fine unless the file is enormous.

You could perform a buffered read of your file from back to front with something like this:

• establish a buffer_size B - this should be longer than the longest anticipated line otherwise you'll need some logic for growing the buffer size when lines are too long
• set offset = file length - buffer_size
• while the offset>=0
  • read buffer_size bytes from offset
  • read a line - it will be incomplete as we'll have jumped into the middle of a line, so we want to ensure the next buffer we read ends with it. Set offset = offset - buffer_size + line length
  • discard that line, read all following lines into an array and reverse them
  • process this array to do whatever you wanted to do