callback functioin

callback機制在系統中運作時機。各層次軟体協同處理時用到。

下層是一個GUI系統，具有繪製介面功能，上層將callback function point傳給下層，而當介面產生事件時，callback function回到上層中,,去執行其行為。

基本:

   1: #include <stdio.h>

   2: #include <stdlib.h>

   3: #include <string.h>

   4: typedef void (*T_SIMPLE_CALLBACK)(void);

   5: void simple_callback(void)

   6: {

   7:     printf("++++simple callback++++++\n");

   8: }

   9:  

  10: void test_simple_callback(T_SIMPLE_CALLBACK p_simple)

  11: {

  12:     printf("=========test the callback function start==\n");

  13:     if(p_simple)//

  14:         (*p_simple)();

  15:     else

  16:         printf("no callback function\n");

  17:     printf("=========test the callback function end==\n");

  18:     return;

  19: }

  20:  

  21: int main()

  22: {

  23: test_simple_callback(simple_callback);

  24: return 0;

  25: }

由結果看出其，在test_simple_callback function執行中，實際上透過參數傳遞進來的函數指標呼叫了回呼函數simple_callback。

其順序為main->test_simple_callback—>simple_callback。而main及simple_callback為上層模組;而test_simple_callback為下層。故當在test_simple_callback中時，called 屬於上層的simple_callback時。即為callback 。

 

干預的callback

典型callback function,含有二個整數參數及整數的返回值。第一個參數是由下層定義的，第二個參數由下層定義，返回值是經由上層經由callback functiion回授給下層的。

   1: #include <stdio.h>

   2: #include <stdlib.h>

   3: #include <string.h>

   4: typedef void (*T_SIMPLE_CALLBACK)(void);

   5: typedef unsigned int (*T_FULL_CALLBACK)(unsigned int para1,unsigned int para2);

   6: void simple_callback(void)

   7: {

   8:     printf("++++simple callback++++++\n");

   9: }

  10: unsigned int full_callback(unsigned int para1,unsigned int para2)

  11: {

  12:     printf("++++full callback++++++\n");

  13:     printf("+para1 :%d, +para2 :%d\n",para1 ,para2 );

  14:     return para2 +para1 ;

  15: }

  16:  

  17: void test_full_callback(T_FULL_CALLBACK p_full,unsigned int para2 )

  18: {

  19:     unsigned int para_callback;

  20:     unsigned int ret_callback;

  21:     para_callback =100;

  22:     printf("===test_full_call_begin\n");

  23:     if(p_full)

  24:     {

  25:         ret_callback =(*p_full)(para_callback ,para2);

  26:         printf("====ret_callback=%d===\n", ret_callback);

  27:     }

  28:     else

  29:         printf("------no_callback----\n");

  30:     printf("===test_full_callback end====\n");

  31:  

  32:  

  33: }

  34:  

  35: void test_simple_callback(T_SIMPLE_CALLBACK p_simple)

  36: {

  37:     printf("=========test the callback function start==\n");

  38:     if(p_simple)//

  39:         (*p_simple)();

  40:     else

  41:         printf("no callback function\n");

  42:     printf("=========test the callback function end==\n");

  43:     return;

  44: }

  45:  

  46: int main()

  47: {

  48: //test_simple_callback(simple_callback);

  49: test_full_callback(full_callback ,1234);

  50: return 0;

  51: }

在full_callback 中,第一參數是由下層給的，代表著下層的狀態；而第二個則是main經由test_full_callback間接再給full_callback用著表示上層的資訊。而full_callback function依這二值去運作，並在full_callback返回(到下層)去確定其執行情況。

"透過callback functiion干預了下層模組的執行"

 

callback function 使用

使用C語言中，標準函式庫中的函式qsort(void *base,size_t nmemb,size_t size,int(*compar)(const void *,const void *));

其中

• base:排序的陣列開頭
  
• nmemb:陣列中元素數量
  
• size:每一個元素的大小
  
• compara:為一個函式指標，用來判斷二個元素間的大小關係，若第一個參數值大於第二個則傳回大於0的值；相等時傳回0及小於時傳回小於0值。

   1: #include <stdio.h>

   2: #include <stdlib.h>

   3: #include <string.h>

   4:  

   5: #define ARRAY_MAX 5

   6: int array_1[ARRAY_MAX]={23,46,19,77,35};

   7: static int sort_int_function(const void *a,const void *b)

   8: {

   9:     return *(int*)a-*(int*)b;

  10: }

  11:  

  12:  

  13: int main()

  14: {

  15:     int i;

  16:     printf("====befor sort===\n");

  17:     for(  i = 0; i < ARRAY_MAX; i += 1)

  18:     {

  19:         printf("array[%d]:%d\n", i, array_1[i]);

  20:  

  21:     }

  22:     qsort((void*)array_1,ARRAY_MAX,sizeof(int),sort_int_function);

  23:     printf("====after sort===\n");

  24:     for(  i = 0; i < ARRAY_MAX; i += 1)

  25:     {

  26:         printf("array[%d]:%d\n", i, array_1[i]);

  27:  

  28:     }

  29:  

  30: return 0;

  31: }