Objective-C 101（保留与分配）NSString

使用Objective-C编程语言，我们可以创建和操作字符串。在Objective-C中，字符串是由NSString类表示的。通过使用NSString类，我们可以对字符串进行各种操作，包括拼接、截取、查找和替换等。

objective-c
NSString *str1 = [[NSString alloc] initWithString:@"Hello World!"];
NSString *str2 = @"Hello Objective-C!";

objective-c
NSString *str1 = @"Hello";
NSString *str2 = @" Objective-C!";
NSString *result = [str1 stringByAppendingString:str2];
NSLog(@"%@", result); // 输出：Hello Objective-C!

objective-c
NSString *str = @"Hello Objective-C!";
NSUInteger length = [str length];
NSLog(@"字符串长度：%lu", length); // 输出：字符串长度：19

objective-c
NSString *str = @"Hello Objective-C!";
NSString *substring1 = [str substringFromIndex:6];
NSString *substring2 = [str substringToIndex:5];
NSLog(@"%@", substring1); // 输出：Objective-C!
NSLog(@"%@", substring2); // 输出：Hello

objective-c
NSString *str = @"Hello Objective-C!";
NSString *newStr = [str stringByReplacingOccurrencesOfString:@"Objective-C" withString:@"Swift"];
NSLog(@"%@", newStr); // 输出：Hello Swift!

objective-c
NSString *str1 = @"Hello";
NSString *str2 = @"Hello";
NSString *str3 = @"World";
BOOL isEqual1 = [str1 isEqualToString:str2];
BOOL isEqual2 = [str1 isEqualToString:str3];
NSLog(@"str1和str2相等：%d", isEqual1); // 输出：str1和str2相等：1
NSLog(@"str1和str3相等：%d", isEqual2); // 输出：str1和str3相等：0