What does write() write if null terminator is already reached?

Question

For write(fd[1], string, size) - what would happen if string is shorter than size?

I looked up the man page but it doesn't clearly specify that situation. I know that for read, it would simply stop there and read whatever string is, but it's certainly not the case for write. So what is write doing? The return value is still size so is it appending null terminator? Why doesn't it just stop like read.

Answer 1

When you call write(), the system assumes you are writing generic data to some file - it doesn't care that you have a string. A null-terminated string is seen as a bunch of non-zero bytes followed by a zero byte - the system will keep writing out until it's written size bytes.

Thus, specifying size which is longer than your string could be dangerous. It's likely that the system is reading data beyond the end of the string out your file, probably filled with garbage data.