![]() ![]() ![]() ![]() Many "pure" object-oriented languages do not support function pointers. They are also used as callback functions if it is necessary to use a member function as a callback function. Functors are more powerful than simple function pointers, being able to contain their own data values, and allowing the programmer to emulate closures. A functor is an object of a class type that implements the function-call operator, allowing the object to be used within expressions using the same syntax as a function call. The two sums are written to the standard output by main.įunctors, or function objects, are similar to function pointers, and can be used in similar ways. Function compute_sum in turn invokes one of the two functions indirectly by dereferencing its function pointer argument funcp multiple times, adding together the values that the invoked function returns and returning the resulting sum. The program operates by having function main call function compute_sum twice, passing it a pointer to the library function sin the first time, and a pointer to function cos the second time. The following C program uses a function pointer to invoke one of two functions ( sin or cos) indirectly from another function ( compute_sum). Such pointers in older languages are generally less type-safe than in more modern languages, though, since the latter associate more typing information with a function pointer variable, such as the data type of the return value of the function and the data type information of the parameters to the function. 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. The simplest implementation of a function (or subroutine) pointer is as a variable containing the address of the function within executable memory. ![]()
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