This was asked to me in an interview! i really got confused
could anybody please help?
Here's a straightforward, mechanical method for figuring out hairy declarations: a -- a a[N] -- is an N-element array *a[N] -- of pointers (*a[N])() -- to functions *(*a[N])() -- returning pointers (*(*a[N])())() -- to functions *(*(*a[N])())() -- returning pointers char *(*(*a[N])())() -- to char.
Return Function Pointer From Function: To return a function pointer from a function, the return type of function should be a pointer to another function. But the compiler doesn't accept such a return type for a function, so we need to define a type that represents that particular function pointer.
int (*f) (int * ): A pointer to a function that takes an integer pointer as argument and returns an integer.
A whole array cannot be passed as an argument to a function in C++. You can, however, pass a pointer to an array without an index by specifying the array's name. In C, when we pass an array to a function say fun(), it is always treated as a pointer by fun(). The below example demonstrates the same.
Typedefs are for wusses. Here's a straightforward, mechanical method for figuring out hairy declarations:
a -- a
a[N] -- is an N-element array
*a[N] -- of pointers
(*a[N])() -- to functions
*(*a[N])() -- returning pointers
(*(*a[N])())() -- to functions
*(*(*a[N])())() -- returning pointers
char *(*(*a[N])())() -- to char.
So, the answer is in the neighborhood of char *(*(*a[N])())();
. I say "in the neighborhood" since it's never specified what arguments the functions take.
It's an obnoxious interview question (types this ugly are truly rare IME), but it does give the interviewer an idea of how well you understand declarators. Either that or they were bored and just wanted to see if they could make your brain sieze.
EDIT
Most everyone else recommends using typedefs. The only time I recommend using a typedef is if the type is intended to be truly opaque (i.e., not manipulated directly by the programmer, but passed to an API, sort of like the FILE type). Otherwise, if the programmer is meant to manipulate objects of that type directly, then IME it's better to have all that information available in the declaration, ugly as it may be. For example, something like
NameFuncPickerPointer a[N];
gives me no information on how to actually use a[i]
. I don't know that a[i]
is callable, or what it returns, or what arguments it should take (if any), or much of anything else. I have to go looking for the typedef
typedef char *NameFunc();
typedef NameFunc *NameFuncPicker();
typedef NameFuncPicker *NameFuncPickerPointer;
and from that puzzle out how to write the expression that actually calls one of the functions. Whereas using the "naked", non-typedef'd declaration, I know immediately that the structure of the call is
char *theName = (*(*a[i])())();
typedef char* (* tCharRetFunc)();
typedef tCharRetFunc (* tFuncRetCharFunc)();
tFuncRetCharFunc arr[N];
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