Question

我在设置传递指向nil的指针时遇到问题。当我通过GDB运行以下代码时，我看到传递的变量“string”在被调用函数中被本地设置为nil，但是在调用它的范围内，它仍然指向原始内存地址。我认为这个问题的解决方案将涉及一个引用和解引用运算符的组合，我只是在基本面上不够好，无法计算出这个：）

#import "AppDelegate.h"


@interface AppDelegate()

+(void)releaseAndNullify:(id)input;

@end


@implementation AppDelegate
@synthesize window;


-(void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
 NSString *string = [NSString string];
 [AppDelegate releaseAndNullify:string];
}


+(void)releaseAndNullify:(id)input
{
 if (input)
 {
  [input release];
  input = nil;
 }
}


-(void)dealloc
{
 [window release];

 [super dealloc];
}


@end

Answer 1

Objective-C参数按值传递，而不是参考。

Answer 2

以下是我从另一篇文章中找到的解决方法：

#import "AppDelegate.h"


@interface AppDelegate()

+(void)releaseAndNullify:(NSString **)input;

@end


@implementation AppDelegate
@synthesize window;


-(void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
 NSString *string = [NSString string];
 [AppDelegate releaseAndNullify:&string];
}


+(void)releaseAndNullify:(NSString **)input
{
 if (!*input) return;

 [*input release];
 *input = nil;
}


-(void)dealloc
{
 [window release];

 [super dealloc];
}


@end

Objective-C：将传递的指针设置为nil

2 个答案: