在objective C中字符串值总是显示为nil。

I have upgraded to Xcode 5.0. And when I run an app in debug mode and try to print an NSString value in console, it gives me the below error. Any ideas?

我已经升级到Xcode 5.0。当我在调试模式下运行一个应用程序并尝试在控制台打印一个NSString值时，它会给我下面的错误。什么好主意吗?

error: warning: couldn't get cmd pointer (substituting NULL): Couldn't load '_cmd' because its value couldn't be evaluated
Couldn't materialize struct: the variable 'stringValue' has no location, it may have been optimized out
Errored out in Execute, couldn't PrepareToExecuteJITExpression

Here is the code:

这是代码:

NSString *stringValue = [[self.responseArray objectAtIndex:i] valueForKey:@"merchant_name"];

4 个解决方案

#1

The reason is stated in the error message: it may have been optimized out.. this means that you are compiling and running your code in an optimized manner.

原因在错误信息中说明:它可能已经被优化了。这意味着您正在以优化的方式编译和运行代码。

you gotta change your compiler optimization level from Fastest,Smallest to none:

您必须将编译器优化级别从最快的、最小的更改为无:

go to your target build settings
转到目标构建设置
search for optimization level
搜索优化级别
change it to none (whatever mode you are in ie debugging, distribution or release)
将其更改为none(无论您在ie调试、发布或发布中的模式是什么)
profit
利润

do the same for your project settings

对你的项目设置做同样的事情

#2

Make sure you are in debug mode. Go Edit Scheme > Build Configuration > Debug

确保处于调试模式。去编辑方案>构建配置>调试

#3

You might be trying to debug in the "release Scheme". Go to "Product/Scheme/Edit Scheme" and pick the "run" in the left panel. Then change the build configuration to "debug".

您可能正在“发布方案”中调试。转到“Product/Scheme/Edit Scheme”并在左侧面板中选择“run”。然后将构建配置更改为“debug”。

#4

One alternate answer: instead of fixing "it may have been optimized out" by removing the optimization, you can stop it from being optimized by using the variable.

另一种解决方案是:不要通过删除优化来修复“它可能已经被优化了”，您可以通过使用变量来阻止优化。

So, in your question, if you do something with stringValue:

在你的问题中，如果你用stringValue做某事:

NSString *stringValue = [[self.responseArray objectAtIndex:i] valueForKey:@"merchant_name"]; 
NSLog(@"%@", stringValue);

stringValue will no longer be optimized out because you're using it.

stringValue将不再被优化，因为你正在使用它。

If you want to see all instances of optimized-out variables in your project, Use Product -> Analyze to analyze your project. Any "Dead store" warnings (in which a value is stored, and never read) will be optimized out at compile time if you have compiler optimization turned on.

如果您想查看项目中所有优化的变量实例，请使用Product ->分析来分析您的项目。如果打开了编译器优化，那么任何“死存储”警告(其中存储了一个值，并且从未读取)都将在编译时进行优化。

#1