What is the difference between read() and fread()?

read is a syscall, whereas fread is a function in the C standard library.

read() is a low level, unbuffered read. It makes a direct system call on UNIX.

fread() is part of the C library, and provides buffered reads. It is usually implemented by calling read() in order to fill its buffer.

As I remember it the read() level APIs do not do buffering - so if you read() 1 byte at a time you will have a huge perf penalty compared to doing the same thing with fread(). fread() will pull a block and dole it out as you ask for it. read() will drop to the kernel for each call.

Family read() -> open, close, read, write
Family fread() -> fopen, fclose, fread, fwrite

Family read:

• are system calls
• are not formatted IO: we have a non formatted byte stream

Family fread

• are functions of the standard C library (libc)
• use an internal buffer
• are formatted IO (with the "%.." parameter) for some of them
• use always the Linux buffer cache

More details here, although note that this post contains some incorrect information.