Objective-C中的字符串比較

Objective-C中，NSString的==操做符比較的是字符串地址，不是字符串內容，若是須要比較內容則須要使用isEqualToString:方法。具體的介紹能夠看這裏：http://iphonedevelopertips.com/cocoa/compare-nsstrings-objects.html 可是Xcode會對部分字符串作優化，相同的字符串會使用同一份拷貝，因此有時候也會出現意想不到的「正確」結果，好比：

 

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NSString *str1 = @"Homebrew"; NSString *str2 = @"Homebrew";   // This compares the addresses of the string if (str1 == str2)   NSLog (@"str1 equals str2"); else   NSLog (@"str1 does not equal str2");

這段代碼會打印出 str1 equals str2，可是這樣就不會：

 

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// Create a C string char *cStr = "Homebrew"; NSString *str3 = [NSString stringWithUTF8String:cStr]; NSString *str4 = @"Homebrew";   // Wrong - this compares the address of the string if (str3 == str4)   NSLog (@"str3 equals str4"); else   NSLog (@"str3 does not equal str4");

 

另外，正確的字符串內容比較方法爲：

 

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char *cStr = "Homebrew"; NSString *str3 = [NSString stringWithUTF8String:cStr]; NSString *str4 = @"Homebrew";   if ([str3 isEqualToString:str4])   NSLog (@"str3 equals str4"); else   NSLog (@"str3 does not equal str4");

來源：http://all-ipad.net/string-compare-in-objective-c/?utm_source=rss&utm_medium=rss&utm_campaign=string-compare-in-objective-c