Objective-C 傳遞函數的指針

Objective-C語言的編程語言允許傳遞一個指向函數的指針。要做到這一點，簡單地聲明一個指針類型的函數參數。

下面以一個簡單的例子，我們通過一個unsigned long的函數指針和更改的函數反映在調用函數裏面的值：

#import <Foundation/Foundation.h> @interface SampleClass:NSObject - (void) getSeconds:(int *)par; @end @implementation SampleClass - (void) getSeconds:(int *)par{ /* get the current number of seconds */ *par = time( NULL ); return; } @end int main () { int sec; SampleClass *sampleClass = [[SampleClass alloc]init]; [sampleClass getSeconds:&sec]; /* print the actual value */ NSLog(@"Number of seconds: %d
", sec ); return 0; }

上面的代碼編譯和執行時，它會產生以下結果：

2013-09-13 23:50:47.572 demo[319] Number of seconds: 1379141447

函數，它可以接受一個指針，也可以接受一個數組，如下面的示例中所示：

#import <Foundation/Foundation.h> @interface SampleClass:NSObject /* function declaration */ - (double) getAverage:(int *)arr ofSize:(int) size; @end @implementation SampleClass - (double) getAverage:(int *)arr ofSize:(int) size { int i, sum = 0; double avg; for (i = 0; i < size; ++i) { sum += arr[i]; } avg = (double)sum / size; return avg; } @end int main () { /* an int array with 5 elements */ int balance[5] = {1000, 2, 3, 17, 50}; double avg; SampleClass *sampleClass = [[SampleClass alloc]init]; /* pass yiibaier to the array as an argument */ avg = [sampleClass getAverage: balance ofSize: 5 ] ; /* output the returned value */ NSLog(@"Average value is: %f
", avg ); return 0; }

當上面的代碼一起編譯和執行時，產生以下結果：

2013-09-14 00:02:21.910 demo[9641] Average value is: 214.400000