mmap() is standardized by POSIX:
mmap
So, it's not included in the C standard library, but it is available on Linux, MacOS, AIX, etc.
mmap() tells the system to map a file to the process's virtual memory. read() and its derivatives (fgetc(), etc.) get bytes from a file and copy them into a user-supplied buffer. In the ideal case, mmap() can allow for faster access because you don't need to copy into an intermediate buffer. Also, the C standard functions fgetc() and friends operate on FILE streams, not directly on files. In that case you're copying from the file into a FILE buffer and then possibly into a user-supplied buffer.
mmap() isn't certain to make your program faster, but it will make your program more complicated and less portable.
If your program is heavy on I/O and a profiler tells you that you're spending a lot of time in read/write syscalls, then you might consider switching to mmap() and see whether performance improves. Otherwise, I'd stick with the standard functions.
Originally Posted by CodeMonkey
