Objective-C 将指针传递给函数

Objective-C 编程语言允许您传递指向函数的指针。为此，只需将函数参数声明为指针类型。

下面是一个简单的例子，我们将一个无符号长指针传递给一个函数，并更改函数内部的值，该值反映在调用函数中:

#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\n", sec );
  return 0;
}

结果如下:

2022-07-07 23:50:47.572 demo[319] Number of seconds: 1379141447

该函数可以接受指针，也可以接受数组，如下例所示:

#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 pointer to the array as an argument */
  avg = [sampleClass getAverage: balance ofSize: 5 ] ;
  /* output the returned value */
  NSLog(@"Average value is: %f\n", avg );
  return 0;
}

结果如下:

2022-07-07 00:02:21.910 demo[9641] Average value is: 214.400000