Safe KVC macro by Andrew Pouliot. In the public domain.

gistfile1.txt

//o is an object type, k is the key on which to check validity
//returns a NSString constant of the relevant key

#define KVC(o, k) (0 && sizeof(o.k) ? @#k : @#k)

//Usage:
ObjectWithMethodCalledKeyName *object = ...;
[object addObserver:self forKeyPath:KVC(object, keyName) options:0 context:NULL];