可变参数函数 - 调用 [obj release] 时的 EXC_BAD_ACCESS；

发布于 2024-09-02 05:23:18 字数 650 浏览 8 评论 0原文

我有以下方法：

(void)makeString:(NSString *)str1,... {

 va_list 字符串；

   NSString *innerText = [[NSString alloc] init];
   NSString *tmpStr = [[NSString alloc] init];

   如果（str1）{

       va_start(字符串, str1); 

       while (tmpStr = va_arg(字符串, id)) { 
            innerText = [innerText stringByAppendingString:tmpStr];
       }

       label.text = [str1 stringByAppendingString:innerText];
   }

   [tmpStr 释放]；

}

我最终会阅读《Objective C Memory Management》，我确信我会找到这个问题的答案 - 可能与指针和复制有关 - ，但是对于现在，任何人都可以解释为什么我添加 [innerText release]；作为该函数的最后一行，我在运行时收到 EXC_BAD_ACCESS 错误？

原文

I have the following method:

(void)makeString:(NSString *)str1,... {

   va_list strings;

   NSString *innerText = [[NSString alloc] init];
   NSString *tmpStr = [[NSString alloc] init];

   if (str1) {

       va_start(strings, str1); 

       while (tmpStr = va_arg(strings, id)) { 
            innerText = [innerText stringByAppendingString:tmpStr];
       }

       label.text = [str1 stringByAppendingString:innerText];
   }

   [tmpStr release];

}

I will eventually get to Objective C Memory Management reading, where I'm sure I will find the answer to this - probably related to pointers and copying - , but for now, can anyone explain why if I add [innerText release]; as the last line of this function, i get an EXC_BAD_ACCESS error at runtime?

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梦旅人picnic 2024-09-09 05:23:18

首先，您的代码是错误的。
据我所知，您只是连接字符串以将结果分配给 label.text。
我假设 label 是一个 ivar，因此 label.text = ... 是合法的。然后应该执行以下操作：

- (void)makeString: (NSString *)str1, ...
{
   if (str1) {
       NSString *tmpStr;

       va_list strings;
       va_start(strings, str1);
       while (tmpStr = va_arg(strings, id)) {
            str1 = [str1 stringByAppendingString: tmpStr];
       }

       label.text = str1;
   }
}

一些注意事项：

您不应该不释放任何输入参数，除非您的方法是要释放某些内容。
正如第一个答案所述，您不应释放 stringByAppendingString: 的结果，除非
你之前已经保留过它。

[更新]

我更改了答案，因为它包含错误。 label.text = str1 当然应该保留str1（如果它想保留的话）。特别是调用代码不应该不保留str1，除非它想保留它自己。

First, your code is erroneous.
As far as I can see you are only concatenating the strings to assign the result to label.text.
I assume that label is an ivar, so label.text = … ist legal. Then the following should do it:

- (void)makeString: (NSString *)str1, ...
{
   if (str1) {
       NSString *tmpStr;

       va_list strings;
       va_start(strings, str1);
       while (tmpStr = va_arg(strings, id)) {
            str1 = [str1 stringByAppendingString: tmpStr];
       }

       label.text = str1;
   }
}

Some notes:

You should not release any input parameter unless your method is about releasing something.
As the first answer stated, you should not release the result of stringByAppendingString: unless
you have retained it before.

[Update]

I changed the answer because it contained an error. label.text = str1 should retain str1 of course (if it wants to keep it). Especially the calling code should not retain str1 unless it wants to keep it for itself.

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