C program pointer to function

Post as a guest Name. Email Required, but never shown. The Overflow Blog. Podcast Making Agile work for data science. Stack Gives Back Featured on Meta. New post summary designs on greatest hits now, everywhere else eventually. Related Hot Network Questions. Question feed. A function can also return a pointer to the calling function. In this case you must be careful, because local variables of function doesn't live outside the function.

They have scope only inside the function. Hence if you return a pointer connected to a local variable, that pointer will be pointing to nothing when the function ends.

It is possible to declare a pointer pointing to a function which can then be used as an argument in another function. A pointer to a function is declared as follows,. A function pointer can point to a specific function when it is assigned the name of that function. Here s is a pointer to a function sum. Now sum can be called using function pointer s along with providing the required argument values. You will find a lot of complex function pointer examples around, lets see one such example and try to understand it.

It appears complex but it is very simple. Learn CSS. Learn JavaScript. C Language C Tutorial. C Compiler. Standard Template Library. Python Python Tutorial. Python Programs.

Python How Tos. Numpy Module. Matplotlib Module. Tkinter Module. Network Programming with Python. Learn Web Scraping. Functions used as arguments to another function are sometimes called callback functions. Consider a case where you are writing a function to perform a task such as sorting an array , but you want the user to be able to define how a particular part of that task will be performed such as whether the array is sorted in ascending or descending order.

Many comparison-based sorting algorithms work on a similar concept: the sorting algorithm iterates through a list of numbers, does comparisons on pairs of numbers, and reorders the numbers based on the results of those comparisons. Consequently, by varying the comparison, we can change the way the algorithm sorts without affecting the rest of the sorting code. Because our comparison function is going to compare two integers and return a boolean value to indicate whether the elements should be swapped, it will look something like this:.

This is done via a function pointer. Is that cool or what? Now you can have one version that can sort any way the caller desires! Note: If a function parameter is of a function type, it will be converted to a pointer to the function type. This means. This only works for function parameters, not stand-alone function pointers, and so is of somewhat limited use. In this case, as long as the user calls selectionSort normally not through a function pointer , the comparisonFcn parameter will default to ascending.

However, type aliases can be used to make pointers to functions look more like regular variables:. To define a function pointer using this method, declare a std::function object like so:. As you see, both the return type and parameters go inside angled brackets, with the parameters inside parenthesis.

If there are no parameters, the parentheses can be left empty. Much like the auto keyword can be used to infer the type of normal variables, the auto keyword can also infer the type of a function pointer. Function pointers are useful primarily when you want to store functions in an array or other structure , or when you need to pass a function to another function.

Because the native syntax to declare function pointers is ugly and error prone, we recommend using std::function.