[arp242]

There are tons of reasons an fopen() call can fail and sometimes you really want to know why; these pokemon exceptions don't give me that. And your code is racy as files can be created in-between the file_exists() and fopen() calls. Yes, this happens, and in some cases it's a security problem (which is why you need to use mkstemp and not mktemp in C).

[nolok]

The core of PHP is very close to the libc function it offers, and so you will do that in a similar way that you do that in C : call error_get_last(), which gives you the details of the last error.