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Concept
Function pointer
Summary
A function pointer, also called a subroutine pointer or procedure pointer, is a pointer referencing executable code, rather than data. Dereferencing the function pointer yields the referenced function, which can be invoked and passed arguments just as in a normal function call. Such an invocation is also known as an "indirect" call, because the function is being invoked indirectly through a variable instead of directly through a fixed identifier or address.
Function pointers allow different code to be executed at runtime. They can also be passed to a function to enable callbacks.
Function pointers are supported by third-generation programming languages (such as PL/I, COBOL, Fortran, dBASE dBL, and C) and object-oriented programming languages (such as C++, C#, and D).
The simplest implementation of a function (or subroutine) pointer is as a variable containing the address of the function within executable memory. Older third-generation languages such as PL/I and COBOL, as well as more modern languages such as Pascal and C generally implement function pointers in this manner.
#Alternate C and C++ syntax
The following C program illustrates the use of two function pointers:
func1 takes one double-precision (double) parameter and returns another double, and is assigned to a function which converts centimeters to inches.
func2 takes a pointer to a constant character array as well as an integer and returns a pointer to a character, and is assigned to a C string handling function which returns a pointer to the first occurrence of a given character in a character array.
#include /* for printf /
#include / for strchr */
double cm_to_inches(double cm) {
return cm / 2.54;
}
// "strchr" is part of the C string handling (i.e., no need for declaration)
// See https://en.wikipedia.org/wiki/C_string_handling#Functions
int main(void) {
double (*func1)(double) = cm_to_inches;
char * (*func2)(const char , int) = strchr;
printf("%f %s", func1(15.0), func2("Wikipedia", 'p'));
/ prints "5.
Official source
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