C++ 语言篇 Pointer to Function

pointer to function

Initialized & Implicit Conversion

  • A [pointer to function] can be initialized with an address of a [non-member function] or a [static member function].
  • [function-to-pointer implicit conversion]
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void f(int);
void (*p1)(int) = &f;
void (*p2)(int) = f; // same as &f, [function-to-pointer implicit conversion]

[this] invokes the [pointed-to function]

  • Unlike [functions] or [references to functions], [pointers to functions] are [objects] and thus can be stored in [arrays, copied, assigned], etc.
  • A [pointer to function] can be used as the [left-hand operand] of the function call operator, [this] invokes the [pointed-to function]:
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int f(int n)
{
std::cout << n << '\n';
return n * n;
}

int main()
{
int (*p)(int) = f;//(int)->argument type
int x = p(7);//p invokes f
}

Dereferencing

Dereferencing a function pointer yields the [lvalue identifying the pointed-to function]:

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int f();
int (*p)() = f;
// pointer p is pointing to f
int (&r)() = *p;
// the [lvalue that identifies f] is bound to a [reference]
r();
// function f invoked through [lvalue reference]
(*p)();
// function f invoked through the [function lvalue]
p();
// function f invoked directly through the [pointer]

Initialized from an overload

A pointer to function may be initialized from an overload set which may include functions, function template specializations, and function templates, if only one overload matches the type of the pointer (see address of an overloaded function for more detail):

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template<typename T> T f(T n) { return n; }
double f(double n) { return n; }

int main()
{
int (*p)(int) = f; // instantiates and selects f<int>
}

Equality comparison operators are defined for pointers to functions (they compare equal if pointing to the same function).


to be continued…

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