getimagesize()

[dud3r]

If getimagesize() fails, how do I make php forward a user to another page?

[Atomiku]

Hmm...

if(!getimagesize()){
   //foward user code here
}

[dud3r]

So you can use that (if!(function){ ) for pretty much anything?

[madwormer2]

Only if the function returns false if it doesn't do what you want it to.

[bradgrafelman]

If you're expecting a function to return FALSE if it fails, the following two expressions are pratically identical:

if(!getimagesize()) {

if(getimagesize() === FALSE) {

Here's the quote from the manual page for [man]getimagesize[/man] that let's you know it returns a bool FALSE:

If accessing the filename image is impossible, or if it isn't a valid picture, getimagesize() will return FALSE and generate an error of level E_WARNING.

Many functions do this, allowing you to use the if(!function()) syntax a lot.