「potentially」解决编译时出现的警告：format string is not a string literal (potentially insecure)

potentially

转载自：http://www.cocoachina.com/bbs/read.php?tid=87645

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：

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);

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：

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