回調(diào)函數(shù)是個(gè)高級(jí)操作技巧，也是日常項(xiàng)目中常常使用到的技能。之所以說回調(diào)函數(shù)是個(gè)高級(jí)操作技巧，是因?yàn)樗尞惒讲僮鞲臃奖?，眾所周知程序?zhí)行分為同步操作和異步操作，同步操作故名思意就是按代碼順序執(zhí)行，而異步則是按需求進(jìn)行回調(diào)執(zhí)行，為了實(shí)時(shí)性一般回調(diào)要盡可能的快進(jìn)快出，避免影響同步操作。下面簡單學(xué)習(xí)一下回調(diào)函數(shù)的不同用法：

| 用法一

相信很多讀者都聽過注冊(cè)回調(diào)，其實(shí)這是兩個(gè)步驟的統(tǒng)稱，先是對(duì)回調(diào)進(jìn)行注冊(cè)，再在特定的場(chǎng)景進(jìn)行回調(diào)，一般會(huì)用在事件觸發(fā)回調(diào)：

#include?"stdio.h"

//?注冊(cè)事件
void?login_event(int?event_type,?void?(*callback)(void))
{
????printf("event?%d?login
",?event_type);
????if?(callback?!=?NULL)
????{
????????callback();
????}
}

//?回調(diào)處理
void?callback_function()
{
????printf("callback?function?handle
");
}

int?main()
{
????login_event(1,?callback_function);
????login_event(2,?NULL);
????return?0;
}

| 用法二

通過參數(shù)對(duì)事件參數(shù)化，簡單理解就是通過輸入?yún)?shù)，判斷回調(diào)函數(shù)觸發(fā)的事件：

#include?"stdio.h"

void?callback_handle(int?state,?int?(*handle)(int))
{
????handle(state);
}

int?handle(int?state)
{
????switch?(state)
????{
????case?0x00:
????????printf("state?%d?handle
",?state);
????????break;
????case?0x01:
????????printf("state?%d?handle
",?state);
????????break;
????case?0x02:
????????printf("state?%d?handle
",?state);
????????break;
????case?0x03:
????????printf("state?%d?handle
",?state);
????????break;
????default:
????????break;
????}
}

int?main()
{
????callback_handle(0,?handle);
????callback_handle(1,?handle);
????return?0;
}
| 用法三

回調(diào)函數(shù)除了常規(guī)用法，還可以通過typedef關(guān)鍵字，把回調(diào)函數(shù)變成一種自定義類型的函數(shù)，這樣就更方便使用：

#include?"stdio.h"

typedef?int?(*callback_t)(int,?int);

int?callback_handle(int?data1,?int?data2,?callback_t?callback)
{
????int?data?=?callback(data1,?data2);
????return?data;
}

int?sum_handle(int?data1,?int?data2)
{
????return?(data1?+?data2);
}

int?minus_handle(int?data1,?int?data2)
{
????return?(data1?-?data2);
}

int?main()
{
????int?user_data?=?0;
????user_data?=?callback_handle(1,?2,?sum_handle);
????printf("user_data:%d
",?user_data);
????user_data?=?callback_handle(2,?1,?minus_handle);
????printf("user_data:%d
",?user_data);
????return?0;
}

| 用法四

回調(diào)函數(shù)除了單個(gè)單獨(dú)使用，還可以同類整合使用，這個(gè)同類是作者本人自認(rèn)為的，通過把一些類似的函數(shù)整合在回調(diào)函數(shù)數(shù)組里：

#include?"stdio.h"

typedef?void?(*callback_t)(int,?int);

void?add_handle(int?a,?int?b)
{
????printf("%d?+?%d?=?%d
",?a,?b,?a?+?b);
}

void?sub_handle(int?a,?int?b)
{
????printf("%d?-?%d?=?%d
",?a,?b,?a?-?b);
}

int?main()
{
????callback_t?callback[2]?=?{add_handle,?sub_handle};
????int?size?=?sizeof(callback)?/?sizeof(callback_t);
????for?(int?i?=?0;?i?

	| 高級(jí)技巧

	眾所周知C語言是面向過程的，但是也可以通過技巧來實(shí)現(xiàn)，這次通過回調(diào)函數(shù)來實(shí)現(xiàn)面向?qū)ο蟮亩鄳B(tài)，多態(tài)按字面的意思就是多種形態(tài)。多態(tài)意味著調(diào)用成員函數(shù)時(shí)，會(huì)根據(jù)調(diào)用函數(shù)的對(duì)象的類型來執(zhí)行不同的函數(shù)，下邊的寫法存在一定的不合理，只是為了展示實(shí)現(xiàn)方式：
#include?"stdio.h"

typedef?struct?overall
{
????void?(*handle)(struct?overall?*);
}?overall_t;

typedef?struct
{
????overall_t?shape;
}?section_1_t;

typedef?struct
{
????overall_t?shape;
}?section_2_t;

void?section_1_handle(overall_t?*shape)
{
????printf("section_1_t?handle
");
}

void?section_2_handle(overall_t?*shape)
{
????printf("section_2_t?handle
");
}

int?main()
{
????overall_t?*overall?=?NULL;
????section_1_t?section_1?=
????????{
????????????.shape?=?{section_1_handle},
????????};
????section_2_t?section_2?=
????????{
????????????.shape?=?{section_2_handle},
????????};
????overall?=?(overall_t?*)§ion_1;
????overall->handle(overall);
????overall?=?(overall_t?*)§ion_2;
????overall->handle(overall);
????return?0;
}
編輯：黃飛