Complicated declarations & definitions
As an aside, once you figure out how the
C and C++ declaration syntax works you can create much more complicated items.
For instance:
//: C03:ComplicatedDefinitions.cpp
/* 1. */ void * (*(*fp1)(int))[10];
/* 2. */ float (*(*fp2)(int,int,float))(int);
/* 3. */ typedef double (*(*(*fp3)())[10])();
fp3 a;
/* 4. */ int (*(*f4())[10])();
int main() {} ///:~
Walk through each one and use the
right-left guideline to figure it out. Number 1 says “fp1 is a
pointer to a function that takes an integer argument and returns a pointer to an
array of 10 void pointers.”
Number 2 says “fp2 is a
pointer to a function that takes three arguments (int, int, and
float) and returns a pointer to a function that takes an integer argument
and returns a float.”
If you are creating a lot of complicated
definitions, you might want to use a typedef. Number 3 shows how a
typedef saves typing the complicated description every time. It says
“An fp3 is a pointer to a function that takes no arguments and
returns a pointer to an array of 10 pointers to functions that take no arguments
and return doubles.” Then it says “a is one of these
fp3 types.” typedef is generally useful for building
complicated descriptions from simple ones.
Number 4 is a function declaration
instead of a variable definition. It says “f4 is a function that
returns a pointer to an array of 10 pointers to functions that return
integers.”
You will rarely if ever need such
complicated declarations and definitions as these. However, if you go through
the exercise of figuring them out you will not even be mildly disturbed with the
slightly complicated ones you may encounter in real life.
