Editing Function pointer (section)

== Alternate C and C++ syntax ==
The C and C++ syntax given above is the canonical one used in all the textbooks - but it's difficult to read and explain. Even the above <code>typedef</code> examples use this syntax. However, every C and C++ compiler supports a more clear and concise mechanism to declare function pointers: use <code>typedef</code>, but ''don't'' store the pointer as part of the definition. Note that the only way this kind of <code>typedef</code> can actually be used is with a pointer - but that highlights the pointer-ness of it.

=== C and C++ ===
<syntaxhighlight lang="C">
// This declares 'F', a function that accepts a 'char' and returns an 'int'. Definition is elsewhere.
int F(char c);

// This defines 'Fn', a type of function that accepts a 'char' and returns an 'int'.
typedef int Fn(char c);

// This defines 'fn', a variable of type pointer-to-'Fn', and assigns the address of 'F' to it.
Fn *fn = &F;      // Note '&' not required - but it highlights what is being done.

// This calls 'F' using 'fn', assigning the result to the variable 'a'
int a = fn('A');

// This defines 'Call', a function that accepts a pointer-to-'Fn', calls it, and returns the result
int Call(Fn *fn, char c) {
   return fn(c);
} // Call(fn, c)

// This calls function 'Call', passing in 'F' and assigning the result to 'call'
int call = Call(&F, 'A');   // Again, '&' is not required

// LEGACY: Note that to maintain existing code bases, the above definition style can still be used first;
// then the original type can be defined in terms of it using the new style.

// This defines 'PFn', a type of pointer-to-type-Fn.
typedef Fn *PFn;

// 'PFn' can be used wherever 'Fn *' can
PFn pfn = F;
int CallP(PFn fn, char c);
</syntaxhighlight>

=== C++ ===
These examples use the above definitions. In particular, note that the above definition for <code>Fn</code> can be used in pointer-to-member-function definitions:
<syntaxhighlight lang="CPP">
// This defines 'C', a class with similar static and member functions,
// and then creates an instance called 'c'
class C {
public:
static int Static(char c);
int Member(char c);
} c; // C

// This defines 'p', a pointer to 'C' and assigns the address of 'c' to it
C *p = &c;

// This assigns a pointer-to-'Static' to 'fn'.
// Since there is no 'this', 'Fn' is the correct type; and 'fn' can be used as above.
fn = &C::Static;

// This defines 'm', a pointer-to-member-of-'C' with type 'Fn',
// and assigns the address of 'C::Member' to it.
// You can read it right-to-left like all pointers:
// "'m' is a pointer to member of class 'C' of type 'Fn'"
Fn C::*m = &C::Member;

// This uses 'm' to call 'Member' in 'c', assigning the result to 'cA'
int cA = (c.*m)('A');

// This uses 'm' to call 'Member' in 'p', assigning the result to 'pA'
int pA = (p->*m)('A');

// This defines 'Ref', a function that accepts a reference-to-'C',
// a pointer-to-member-of-'C' of type 'Fn', and a 'char',
// calls the function and returns the result
int Ref(C &r, Fn C::*m, char c) {
   return (r.*m)(c);
} // Ref(r, m, c)

// This defines 'Ptr', a function that accepts a pointer-to-'C',
// a pointer-to-member-of-'C' of type 'Fn', and a 'char',
// calls the function and returns the result
int Ptr(C *p, Fn C::*m, char c) {
   return (p->*m)(c);
} // Ptr(p, m, c)

// LEGACY: Note that to maintain existing code bases, the above definition style can still be used first;
// then the original type can be defined in terms of it using the new style.

// This defines 'FnC', a type of pointer-to-member-of-class-'C' of type 'Fn'
typedef Fn C::*FnC;

// 'FnC' can be used wherever 'Fn C::*' can
FnC fnC = &C::Member;
int RefP(C &p, FnC m, char c);
</syntaxhighlight>