函数指针的用途是什么，我将如何使用它们? [英] What are function pointers used for, and how would I use them?

问题描述

我知道我可以使用函数的指针.

I understand I can use pointers for functions.

有人可以解释为什么要使用它们，以及如何使用?简短的示例代码对我很有帮助.

Can someone explain why one would use them, and how? Short example code would be very helpful to me.

推荐答案

一个简单的例子是这样的:根据业务逻辑，你有一组操作(函数).您有一个散列函数，可以将输入问题减少到业务逻辑函数之一.干净的代码会有一个函数指针数组，您的程序将从输入中推导出该数组的索引并调用它.

A simple case is like this: You have an array of operations (functions) according to your business logic. You have a hashing function that reduces an input problem to one of the business logic functions. A clean code would have an array of function pointers, and your program will deduce an index to that array from the input and call it.

这是一个示例代码:

typedef void (*fn)(void) FNTYPE;
FNTYPE fn_arr[5];

fn_arr[0] = fun1; // fun1 is previously defined
fn_arr[1] = fun2;
...

void callMyFun(string inp) {
    int idx = decideWhichFun(inp); // returns an int between 0 and 4
    fn_arr[idx]();
}

当然，回调是最常见的用法.示例代码如下:

But of course, callbacks are the most common usage. Sample code below:

void doLengthyOperation(string inp, void (*callback)(string status)) {
  // do the lengthy task
  callback("finished");
}

void fnAfterLengthyTask(string status) {
    cout << status << endl;
}

int main() {
    doLengthyOperation(someinput, fnAfterLengthyTask);
}

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