check() is like
assert() in C. If the condition is false, it will stop your program dead with a log message, an error window and - if a debugger is attached - a break into the debugger. You cannot continue execution after this point. It should be used to trap programmer errors that violate assumptions made by the following code - for example, indexing into a
TArray with an invalid index will cause a check failure, because indexing outside of an array is always a programmer error. Additionally, the compiler can optimise code following a
check() with the assumption that the condition is guaranteed true.
if() should be used to handle conditions that are possible (no matter how unlikely) during the execution of your code.
So in the above code, you should use an
if(), as null is a valid result from
UGameplayStatics::GetGameMode(), e.g. you're running on a client.
There is also the
ensure() macro which is halfway between the two - i.e. you expect the condition to always be true, you want to handle it if it isn't, but you also want to be told about it. For example:
AMyGameMode* MyGameMode = UGameplayStatics::GetGameMode();
This should be read in the same way as
if (MyGameMode) except that it will log and break into the debugger if
MyGameMode is null, i.e.
ensure() will return the same thing (converted to bool) as it has been passed. Unlike
check(), you may continue execution of your program after this break.
Each use of
ensure() will also only fire once, so future failures will not keep popping up in the debugger or log. If you want a message, you can use
ensure() also come in
ensureMsgf() flavours which allow you to write out a
printf-style helpful message to indicate the nature of the failure, e.g.:
if (ensureMsgf(MyGameMode, TEXT("Unexpected null game mode! (SomeState: %d)"), SomeState))
Hope this helps,
May 12 '16 at 09:53 AM
Steve Robb STAFF