objective-c - Xcode 警告 : Format specifies type 'long' but the argument has type 'int _Nullable'

Question

我收到以下代码行的警告:

    NSLog(@"selected segment: %li", _segmentControl.selectedSegmentIndex);

属性 selectedSegmentIndex 的类型为 NSInteger。

如果我将格式更改为 %i，我会收到以下警告:

Format specifies type 'int' but the argument has type 'long _Nullable'

Nullable 类型是否有任何新的格式说明符，或者这只是 Xcode 7 中的一个错误？

Answer 1

你应该输入:

NSLog(@"selected segment: %li", (long)_segmentControl.selectedSegmentIndex);

因为 NSInteger 在 32 位和 64 位架构中的长度不同。以前您没有看到警告，因为您可能只针对 64 位架构进行编译。

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我还建议阅读 Apple Article ，因为 Xcode 7 中有新的说明符(其中包括 nullable 和 nonnull)。

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解答你评论中的疑惑，请引用这个Apple document ，他们声明如下:

Type Specifiers

Script action: Warns about potential problems; may generate false negatives.

Typically, in 32-bit code you use the %d specifier to format int values in functions such as printf, NSAssert, and NSLog, and in methods such as stringWithFormat:. But with NSInteger, which on 64-bit architectures is the same size as long, you need to use the %ld specifier. Unless you are building 32-bit like 64-bit, these specifiers generates compiler warnings in 32-bit mode. To avoid this problem, you can cast the values to long or unsigned long, as appropriate. For example:

NSInteger i = 34;
printf("%ld\n", (long)i);