Objective-C語(yǔ)言的編程語(yǔ)言允許傳遞一個(gè)指向函數(shù)的指針。要做到這一點(diǎn)，簡(jiǎn)單地聲明一個(gè)指針類(lèi)型的函數(shù)參數(shù)。
下面以一個(gè)簡(jiǎn)單的例子，我們通過(guò)一個(gè)unsigned long的函數(shù)指針和更改的函數(shù)反映在調(diào)用函數(shù)里面的值：
#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(zhí)行時(shí)，它會(huì)產(chǎn)生以下結(jié)果：
2013-09-13 23:50:47.572 demo[319] Number of seconds: 1379141447
函數(shù)，它可以接受一個(gè)指針，也可以接受一個(gè)數(shù)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(dāng)上面的代碼一起編譯和執(zhí)行時(shí)，產(chǎn)生以下結(jié)果：
2013-09-14 00:02:21.910 demo[9641] Average value is: 214.400000
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