什么是＆QUOT;回调＆QUOT;在C和它们是如何实现的？ [英] What is a "callback" in C and how are they implemented?

问题描述

我是新的C，Objective-C的，并在OSX核心音频节目。从我所做的阅读，核心音频很大程度上依赖于回调（和C ++，但那是另一回事）。我明白建立一个由另一个函数调用的重复完成任务函数的概念（在某种程度上）。我只是不明白它们是如何被建立，他们是如何工作的。任何例子是AP preciated。谢谢你。

I am new to C, Objective-C, and Core Audio programming on OSX. From the reading that I have done, Core Audio relies heavily on callbacks (and C++, but that's another story). I understand the concept (sort of) of setting up a function that is called by another function repeatedly to accomplish a task. I just don't understand how they get set up and how they actually work. Any examples would be appreciated. Thanks.

推荐答案

有在C中没有回调 - 没有比任何其他泛型编程概念的更多

There is no "callback" in C - not more than any other generic programming concept.

他们使用函数指针来实现。这里有一个例子：

They're implemented using function pointers. Here's an example:

void populate_array(int *array, size_t arraySize, int (*getNextValue)(void))
{
    for (size_t i=0; i<arraySize; i++)
        array[i] = getNextValue();
}

int getNextRandomValue(void)
{
    return rand();
}

int main(void)
{
    int myarray[10];
    populate_array(myarray, 10, getNextRandomValue);
    ...
}

在这里， populate_array 函数有一个函数指针作为其第三个参数，调用它来获取值来填充数组。我们已经写回调 getNextRandomValue ，它返回一个随机杂交的价值，并通过一个指向它 populate_array 。 populate_array 将调用回调函数10次，将返回的值给定的数组中的元素。

Here, the populate_array function takes a function pointer as its third parameter, and calls it to get the values to populate the array with. We've written the callback getNextRandomValue, which returns a random-ish value, and passed a pointer to it to populate_array. populate_array will call our callback function 10 times and assign the returned values to the elements in the given array.

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