字符串格式化技巧/文档 [英] String Formatting Tricks/Docs

问题描述

下读书粗野青蛙应对这个帖子，被下面的行$好奇的C $ C：

Was reading the response by Shaggy Frog to this post and was intrigued by the following line of code:

NSLog(@"%@", [NSString stringWithFormat:@"%@:%*s%5.2f", key, padding, " ", [object floatValue]]);

我知道字符串格式化是一种古老的艺术，但我有点做最终绕成可可/的OBJ-C编程和跳了几个档次沿途。哪里是一个很好的（最好）学习的地方所有允许在字符串格式化技巧的NSString的 stringWithFormat ？我熟悉苹果公司的<一个href=\"http://developer.apple.com/mac/library/documentation/cocoa/conceptual/Strings/Articles/formatSpecifiers.html\"相对=nofollow>字符串格式说明页，但我可以告诉它无论是与发生的事情并不揭示％* S 或％5.2f （更不用说3明显占位符后面4个参数）上面？！？

I know string formatting is an age old art but I'm kinda doing the end around into Cocoa/Obj-C programming and skipped a few grades along the way. Where is a good (best) place to learn all the string formatting tricks allowed in NSString's stringWithFormat? I'm familiar with Apple's String Format Specifiers page but from what I can tell it doesn't shed light on whatever is happening with %*s or the %5.2f (not to mention the 3 apparent placeholders followed by 4 arguments) above?!?

推荐答案

的 -stringWithFormat 的带领您到<一个文档href=\"http://developer.apple.com/mac/library/documentation/Cocoa/Conceptual/Strings/Articles/formatSpecifiers.html\"相对=nofollow>字符串格式说明反过来向您发送的的 IEEE的printf规范。这是对尽可能多的信息，你永远想要的。

The documentation of -stringWithFormat leads you to String Format Specifier which in turn sends you to the IEEE printf specification. That's about as much information as you'll ever want.

唯一的例外：

Objective-C的对象，印为
  通过字符串返回
  的 descriptionWithLocale：的如果有的话，
  或说明的其他方式。也适用
  用的 CFTypeRef 的对象，返回
  的结果的 CFCopyDescription 的
  功能。

%@

Objective-C object, printed as the string returned by descriptionWithLocale: if available, or description otherwise. Also works with CFTypeRef objects, returning the result of the CFCopyDescription function.

• 的无的被转换成的（空）的，这就是为什么的NSLog（@％@，someObject）比的NSLog（someObject）后来可能崩溃更安全时的 someObject 的是无的：

• nil gets converted to (null), that's the reason why NSLog(@"%@", someObject) is safer than NSLog("someObject). The later might crash when someObject is nil:

您可能也有兴趣在维基百科关于字符串格式化页。

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