NSLog invalid in Xcode

I am confused for a long time. In my Project, the nslog is invalid,like:

 NSArray *arr = [NSArray arrayWithObjects:@"a",@"b",nil];

NSLog(@"%@",arr);

In the console there is no result. In the debugger, I can see the arr in the local, and when I select:"Print Description to Console", it shows in the console like:

Printing descr开发者_JAVA技巧iption of arr:
(gdb) 

In My Project I use some lib built in C&C++, and I add them as frame work. I find the NSlog always becomes invalid after I create a pthread and do sth using the lib. I've no idea about it and can any give tips?

thanks!

You can try to clean(shift+command+k) your project. It works for me.

Try this way

for(int i=0; i<[arr length]; ++i)
     NSLog(@"%@",arr[i]);