When are you able to return NULL as the returning value of a C function?

Question

I was wondering if you could tell me when you are able to return NULL, as the result of a function in C.

For instance int lenght() can\'t retur

Answer 1

NULL is a pointer value - or rather a null-pointer value.

NULL means that the function can't find where your pointer should point to - for example if you want to open a file, but it doesn't work your file pointer is returned as NULL. So you can test the value of a pointer and check to see if it worked or not.

If you are writing a routine

int length()

then you could return a negative value if length is unable to read the length of whatever you send it - this would be a way of indicating an error, because normally lengths can never be negative....