file scanning

[iwanttolearnc]

I am doing some code in C to scan a file for the occurance of perticular string or pattern. I can implement this by reading the file in some fixed size to a buffer and then searching for the pattern.
The problen is
supposse that part of the pattern exists at the end of the buffer
and then the remaining with come up with te next read only,then
simple string comparison fails.
A simple fix would be to read the whole file in the buffer and then
compare, which is not feassible always.

Can somebody suggest a solution, any idea how file scanners and programs like Grep do it.

The code has to run for windows or linux so I cannot resort to any
MFC , C++ can be used

[redhead]

Just in theory, perhaps not the most convenient way of achieving it, but here it goes.

 
  1) Read the desired buffer_length of the file 
     (could be a single line/ portion of a line/ whatever)
  2) Search for the patern / or as much of the first part of the
     patern, when getting closer than strlen(pattern) to end of buffer
  3) If the first part of the pattern matched at the end of the buffer
     search for the remainder of the pattern as the beginning of the
     next read from file, skipping what ever newline char there might
     have been, if the pattern was split over two lines in the file.

[iwanttolearnc]

thanks redhead
is there any optimised algorithm that can speed up the search process
and is there someother way thst using strstr()to detect the pattern.
A lot of software provides support fot search and replacement so there must be some standard technique.

Speed is of some concern here,it mustn't hog all the CPU time