鍍金池/ 教程/ C/ Objective-C 函數(shù)按值調(diào)用
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Objective-C 函數(shù)按值調(diào)用
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Objective-C 函數(shù)按值調(diào)用

按值傳遞參數(shù)給函數(shù)的方法調(diào)用復(fù)制到正式參數(shù)的函數(shù)參數(shù)的實(shí)際值。在這種情況下，該函數(shù)內(nèi)的參數(shù)所做的更改參數(shù)沒(méi)有影響。

默認(rèn)情況下，使用的Objective-C編程語(yǔ)言調(diào)用值法來(lái)傳遞參數(shù)。在一般情況下，這意味著，在一個(gè)函數(shù)中的代碼可以用來(lái)調(diào)用該函數(shù)的參數(shù)不會(huì)改變?？紤]函數(shù)swap()定義如下：

/* function definition to swap the values */
- (void)swap:(int)num1 andNum2:(int)num2
{
   int temp;

   temp = num1; /* save the value of num1 */
   num1 = num2;    /* put num2 into num1 */
   num2 = temp; /* put temp into num2 */
  
   return;
}

現(xiàn)在，讓我們通過(guò)在下面的示例中的實(shí)際值作為調(diào)用函數(shù)swap()：

#import <Foundation/Foundation.h>

@interface SampleClass:NSObject
/* method declaration */
- (void)swap:(int)num1 andNum2:(int)num2;
@end

@implementation SampleClass

- (void)swap:(int)num1 andNum2:(int)num2
{
   int temp;

   temp = num1; /* save the value of num1 */
   num1 = num2;    /* put num2 into num1 */
   num2 = temp; /* put temp into num2 */
   
}

@end

int main ()
{
   /* local variable definition */
   int a = 100;
   int b = 200;
   
   SampleClass *sampleClass = [[SampleClass alloc]init];

   NSLog(@"Before swap, value of a : %d
", a );
   NSLog(@"Before swap, value of b : %d
", b );
 
   /* calling a function to swap the values */
   [sampleClass swap:a andNum2:b];
 
   NSLog(@"After swap, value of a : %d
", a );
   NSLog(@"After swap, value of b : %d
", b );
 
   return 0;
}

讓我們編譯并執(zhí)行它，它會(huì)產(chǎn)生以下結(jié)果：

2013-09-09 12:12:42.011 demo[13488] Before swap, value of a : 100
2013-09-09 12:12:42.011 demo[13488] Before swap, value of b : 200
2013-09-09 12:12:42.011 demo[13488] After swap, value of a : 100
2013-09-09 12:12:42.011 demo[13488] After swap, value of b : 200

這表明，盡管它們均已改變，在函數(shù)內(nèi)部的值中沒(méi)有任何改變。