Can't allocate a pointer to object of abstract type?

Question

For some reason, I'm not able to initialize a set of pointers to an abstract data type like so:

gkAnimation* run = NULL, walk = NULL, idle = NULL;

I'm getting an error saying:

jni/STEP3D_GK_Wrapper_JNI.cpp:283:34: error: cannot allocate an object of abstract type 'gkAnimation'

I haven't had this issue happen before, and I don't think the class itself is doing anything special for this error to happen or that it would matter. I can post more code if it helps, but I'm pretty stumped here. Any ideas?

I'm not certain I see the error, but I'm going to go with "put all declarations on separate lines" — Mooing Duck, Jul 10 '13 at 20:30

Justin Meiners · Accepted Answer · 2013-07-10T20:02:17.897

8

The problem is that this syntax:

gkAnimation* run = NULL, walk = NULL, idle = NULL;

Does not mean:

gkAnimation* run = NULL;
gkAnimation* walk = NULL;
gkAnimation* idle = NULL;

It means:

gkAnimation* run = NULL;
gkAnimation walk = NULL; /* invalid */
gkAnimation idle = NULL; /* invalid */

You need to explicitly define each item in the list as a pointer:

gkAnimation *run = NULL, *walk = NULL, *idle = NULL;

This is why many prefer the syntax style of placing the pointer next to the variable rather than next to the type.

edited Jul 10 '13 at 20:02

answered Jul 10 '13 at 19:55

Justin Meiners

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...and why many prefer the convention of declaring at most one variable per source line. – Casey Jul 10 '13 at 20:10
@Casey Im not a big fan either. – Justin Meiners Jul 10 '13 at 20:14
1

Thanks, I also found this helpful: http://stackoverflow.com/questions/13618282/c-declaring-multiple-object-pointers-on-one-line-causes-compiler-error – mpellegr Jul 10 '13 at 20:51

Can't allocate a pointer to object of abstract type?

1 Answers1