在Xcode 4.2（iOS 5）之前，我猜大家都和我一样很喜欢下面的调试输出写法：
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NSString
*str = @
"Attention"
;
// first warning
NSLog
(str);
// second warning
NSLog
([str stringByAppendingFormat:@
", %@"
, @
"Xcode 4.2 do not support this format!"
]);
// third warning
NSLog
([
NSString
stringWithFormat:@
"%@, Xcode 4.2 do not support this format!"
, @
"Attention"
]);
// fourth warning
NSException
*exception = [
NSException
exceptionWithName:@
"Attention"
reason:@
"Xcode 4.2 do not support this format!"
userInfo:
nil
];
NSLog
(exception);
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但是在Xcode 4.2(iOS 5)之后，貌似苹果更新的编译器，出了支持ARC的Apple LLVM compiler 3.0。然后我发现每次编译，以前的这些输出都会产生一个warning(警告，黄色三角形)。
在StackOverflow和iPhone Dev SDK查找相关答案之后，发现在最新版的编译器里面NSLog为了安全，只接受格式化的字符串，因为NSLog底层也是用printf来格式化输出的。
所以上面的写法都会给出警告，可以把上面的写法修改为以下合法模式：
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NSString
*str = @
"Attention"
;
// first warning
NSLog
(str);
// warning
NSLog
(@
"%@"
, str);
// solution
NSLog
(str,
nil
);
// solution
// second warning
NSLog
([str stringByAppendingFormat:@
", %@"
, @
"Xcode 4.2 do not support this format!"
]);
// warning
NSLog
(@
"%@"
, [str stringByAppendingFormat:@
", %@"
, @
"Xcode 4.2 do not support this format!"
]);
// solution
NSLog
([str stringByAppendingFormat:@
", %@"
, @
"Xcode 4.2 do not support this format!"
],
nil
);
//solution
// third warning
NSLog
([
NSString
stringWithFormat:@
"%@, Xcode 4.2 do not support this format!"
, @
"Attention"
]);
// warning
NSLog
(@
"%@, Xcode 4.2 do not support this format!"
, @
"Attention"
);
// solution
NSLog
([
NSString
stringWithFormat:@
"%@, Xcode 4.2 do not support this format!"
, @
"Attention"
],
nil
);
// solution
// fourth warning
NSException
*exception = [
NSException
exceptionWithName:@
"Attention"
reason:@
"Xcode 4.2 do not support this format!"
userInfo:
nil
];
NSLog
(exception);
// warning
NSLog
(@
"%@"
, exception);
// solution
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