obj-c中NSString的常用方法

#import <Foundation/Foundation.h>

/**
    NSString中常用的类方法
        + (nullable instancetype)stringWithUTF8String:(const char *)nullTerminatedCString;
            instancetypetype 作为返回值 代表返回的是当前这个类的对象
            作用：将C语言的字符串转化为OC字符串对象
        + (instancetype)stringWithFormat:(NSString *)format, ... NS_FORMAT_FUNCTION(1,2);
            作用：拼接一个字符串对象
    NSString中常用的对象方法
        1). length 方法 返回值 NSUInteger ,得到字符串的字符的个数，可以处理中文
        2). characterAtIndex 得到字符串中指定下标的字符
            - (unichar)characterAtIndex:(NSUInteger)index;
        3). 判断两个字符串是否相等
            - (BOOL)isEqualToString:(NSString *)aString;
        4). 比较字符串大小
            - (NSComparisonResult)compare:(NSString *)string;
            NSComparisonResult :
            typedef NS_CLOSED_ENUM(NSInteger, NSComparisonResult) {
                NSOrderedAscending = -1L,
                NSOrderedSame,
                NSOrderedDescending
            };
 */

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        NSString *str = @"qwertyuiop";
		NSUInteger len = [str length];
        NSLog(@"%ld", len);
		
        unichar ch = [str characterAtIndex:2];
        NSLog(@"ch = %C", ch);
		
		NSString *str1 = @"qq";
        NSString *str2 = [NSString stringWithFormat:@"qq"];
        BOOL b = [str1 isEqualToString:str2];
        NSLog(@"%d", b);
        
        NSComparisonResult res = [str1 compare:str2];
        NSLog(@"%ld", res);
    }
    
    return 0;
}