[SOLVED] How to correctly buffer lines using fread

How to correctly buffer lines using fread

I want to use fread() for IO for some reason (speed and ...). i have a file with different sized lines. by using a code like:

while( !EOF ){ 
  fread(buffer,500MB,1,fileName);
  // process buffer
}

the last line may read incompletely and we have to read the last line again in next trial, so how to force fread() to continue from the beginning of the last line?

or if possible how to force fread() to read more than 500MB untill reaching a \n or another specific character?

Thanks All

Ameer.

Solution

Assuming a bufferof bytes that you have reverse found a \n character in at position pos, then you want to roll back to the length of the buffer minus this pos. Call this step.

You can use fseek to move the file pointer back by this much:

int fseek( FILE *stream, long offset, int origin );

In your case

int ret = fseek(stream, -step, SEEK_END);

This will involve re-reading part of the file, and a fair bit of jumping around - the comments have suggested alternative ways that may be quicker.