下面我們介紹一篇關於iOS NSDateFormatter的NSLocale使用en_US_POSIX還是en_US，希望對加入各位對 NSDateFormatter用法理解。

iOS SDK提供的日期時間格式化對象需要使用到NSLocale對象來控制日期和時間的顯示，en_US為標准的格式往往使用的最多，但是習慣使用Java或C#的朋友會忽略掉iOS SDK提供的另一種格式en_US_POSIX,並且兩種格式運行後的效果完全一樣。

參考代碼；

 代碼如下 復制代碼 NSDateFormatter *formatter1 = [[[NSDateFormatter alloc] init] autorelease];
[formatter1 setLocale:[[[NSLocale alloc] initWithLocaleIdentifier:@"en_US"] autorelease]];
NSDateFormatter *formatter2 = [[[NSDateFormatter alloc] init] autorelease];
[formatter2 setLocale:[[[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"] autorelease]];
 
[formatter1 setDateFormat:@"yyyy/MM/dd HH:mm:ss"];
[formatter2 setDateFormat:@"yyyy/MM/dd HH:mm:ss"];
 
NSDate *date = [NSDate date];
NSLog(@"formatter1:%@",[formatter1 stringFromDate:date]);
NSLog(@"formatter2:%@",[formatter2 stringFromDate:date]);

到底使用en_US_POSIX還是en_US, Apple在SDK文檔中給出了答案.

 代碼如下 復制代碼

In most cases the best locale to choose is “en_US_POSIX”

因為

“en_US_POSIX” is also invariant in time (if the US, at some point in the future, changes the way it formats dates, “en_US” will change to reflect the new behaviour, but “en_US_POSIX” will not), and between machines (“en_US_POSIX” works the same on iPhone OS as it does on Mac OS X, and as it it does on other platforms).