Objective-C 指针传递给函数

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  指针传递给函数

  Objective-C编程语言允许您将指针传递给函数。为此，只需将函数参数声明为指针类型。在一个简单的示例中，我们将一个无符号的长指针传递给一个函数，并更改该函数内部的值，该值会反映在调用函数中-

  
  #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;
  }
  

  
  2020-08-08 10:40:03.005 test[11928:4136] Number of seconds: 1596854402
  

  该函数可以接受一个指针，也可以接受一个数组，如以下示例所示：

  
  @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;
  }
  

  
  2020-08-08 10:42:37.483 test[6612:332] Average value is: 214.400000