Objective-C中,NSString的==操作符比较的是字符串地址,不是字符串内容,如果需要比较内容则需要使用isEqualToString:方法。具体的介绍可以看这里. 但是Xcode会对部分字符串做优化,相同的字符串会使用同一份拷贝,所以有时候也会出现意想不到的“正确”结果,比如:
- 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");
这段代码会打印出 str1 equals str2,但是这样就不会:
- // 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,正确的字符串内容比较方法为:
- 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");
原文地址:http://all-ipad.net/string-compare-in-objective-c/?utm_source=rss&utm_medium=rss&utm_campaign=string-compare-in-objective-c