What does the error message "invalid application of ‘sizeof’ to incomplete type" generally indicate in programming, particularly in C or C++?
a) The code is attempting to use the sizeof operator on a type that has been declared but not fully defined.
b) The sizeof operator is being used on a type that is not recognized by the compiler.
c) The sizeof operator is applied to a pointer type, which is invalid.
d) The sizeof operator is being used in a way that is incompatible with the system architecture.