基本的Objective-C的语法：＆QUOT;％@＆QUOT;？ [英] Basic Objective-C syntax: "%@"?
问题描述
我正在通过斯坦福iPhone播客和有一些基本的问题。
I'm working through the Stanford iPhone podcasts and have some basic questions.
第一：为什么没有简单的字符串连接？ （还是我只是缺少了吗？）
The first: why is there no easy string concatenation? (or am I just missing it?)
我需要与下面的NSLog的帮助，不知道它目前在做什么（在％@一部分）。你刚刚替补那些你需要的地方串联，然后逗号值在最后分开的？
I needed help with the NSLog below, and have no idea what it's currently doing (the %@ part). Do you just substitute those in wherever you need concatenation, and then comma separate the values at the end?
NSString *path = @"~";
NSString *absolutePath = [path stringByExpandingTildeInPath];
NSLog(@"My home folder is at '%@'", absolutePath);
而与任何其他编程语言我会做它是这样的：
whereas with any other programing language I'd have done it like this:
NSLog(@"My home folder is at " + absolutePath);
谢谢！ （此外，任何好的导游/有人熟悉Java / C＃/等风格的语法转换到Objective-C的？引用）
Thanks! (Additionally, any good guides/references for someone familiar with Java/C#/etc style syntax transitioning to Objective-C?)
推荐答案
％@ 是在格式字符串中的占位符，一个NSString的实例。
%@ is a placeholder in a format string, for a NSString instance.
当你做这样的事情：
NSLog(@"My home folder is at '%@'", absolutePath);
您是说的NSLog与absolutePath字符串值替换％@ 占位符。
You are saying NSLog to replace %@ placeholder with absolutePath string value.
同样的，如果你把更多的占位符，可以指定多个值，以取代那些占位符是这样的：
Likewise, if you put more placeholders, you can specify more values to replace those placeholders like this:
NSString *absolutePath = @"/home/whatever";
NSLog(@"My home #%d folder is at '%@'", 5, absolutePath);
将会打印：
我家＃5是的/ home /不管
My home #5 is at /home/whatever
一个简单的方法做字符串连接：
An easy way to do string concatenation:
NSString *s1 = @"Hello, ";
NSString *s2 = @"world.";
NSString *s = [NSString stringWithFormat:@"%@%@", s1, s2];
// s will be "Hello, world."
您不能 + 符号作为字符串串连运营商，因为没有运行在Objective-C超载。
You can't have + sign as a string concatenate operator, since there is no operation overloading in Objective-C.
希望它帮助。
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