What do parentheses in a C variable declaration mean?

Question

Can someone explain what this means?

int (*data[2])[2]; 

Answer 1

What are the parentheses for?

In C brackets [] have a higher precedence than the asterisk *

Good explanation from Wikipedia:

To declare a variable as being a pointer to an array, we must make use of parentheses. This is because in C brackets ([]) have higher precedence than the asterisk (*). So if we wish to declare a pointer to an array, we need to supply parentheses to override this:

double (*elephant)[20]; 

This declares that elephant is a pointer, and the type it points at is an array of 20 double values.

To declare a pointer to an array of pointers, simply combine the notations.

int *(*crocodile)[15]; 

Source.

And your actual case:

int (*data[2])[5]; 

data is an array of 2 elements. Each element contains a pointer to an array of 5 ints.

So you you could have in code using your 'data' type:

int (*data[2])[5]; int x1[5]; data[0] = &x1; data[1] = &x1;  data[2] = &x1;//<--- out of bounds, crash data has no 3rd element int y1[10]; data[0] = &y1;//<--- compiling error, each element of data must point to an int[5] not an int[10] 

Answer 2

There is a very cool program called "cdecl" that you can download for Linux/Unix and probably for Windows as well. You paste in a C (or C++ if you use c++decl) variable declaration and it spells it out in simple words.