Does Cocoa’s printf-style formatting not work as expected when using %@ conversion specifier and field width?

My understanding of printf-like format strings is that you can prefix any conve开发者_如何学运维rsion specifier with a minimum field width. This does not seem to work for Cocoa’s %@ specifier. Example:

NSLog(@"'%5@'", @"foo");
NSLog(@"'%5s'", [@"foo" UTF8String]);

Output:

… 'foo'
… '  foo'

Is this the intended behavior?

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%@ is only for objective-c object. Thus, the field width will be invalid, if the object is not NSString.

I didn't know that %5@ is formatted to be the same as %@.

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The %@ format specifier just gets replaced by the object's description. It doesn't do any truncation or padding.