Objective-C 传递函数的指针
Objective-C语言的编程语言允许传递一个指向函数的指针。要做到这一点,简单地声明一个指针类型的函数参数。
下面以一个简单的例子,我们通过一个unsigned long的函数指针和更改的函数反映在调用函数里面的值:
#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; }
上面的代码编译和执行时,它会产生以下结果:
2013-09-13 23:50:47.572 demo[319] Number of seconds: 1379141447
函数,它可以接受一个指针,也可以接受一个数组,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; }
当上面的代码一起编译和执行时,产生以下结果:
2013-09-14 00:02:21.910 demo[9641] Average value is: 214.400000