ios_nsstirng 知识点总结

//**************************************************************
                    // NSString
    //**************************************************************
    //oc所有的内存存储区间数据区，堆区，栈区，代码区
     //----------------创建字符串的方法----------------
//1.字符串常量创建
     NSString *string_1 = @"wellcome to it";
     
//2、通过实例化方法 initWithString:实例化一个字符串对象
     NSString *string_2 = [[NSString alloc] initWithString:string_1];
     //NSString *string_3 = [[NSString alloc] initWithString:@"i love it"];//多余
     NSLog(@"%@",string_2);
     
//3、用标准c创建字符串: initWithCString:encoding:方法
     char *str = "i love iOS" ;
     NSString *string_4 = [[NSString alloc]initWithCString:str encoding:NSUTF8StringEncoding];
     NSLog(@"%@",string_4);
     //或者:用 initWithUTF8String:实例化一个字符串对象
     NSString *string_5 = [[NSString alloc]initWithUTF8String:str];
     NSLog(@"%@",string_5);
     
//4、创建格式化字符串:占位符(由一个%加一个字符组成)
     int age = 23;
     NSString *name = @"陈梁";
     NSString *string_6 = [[NSString alloc]initWithFormat:@"i an %@,and age is %i 。" ,name ,age ];
     NSLog(@"%@",string_6);
     
//5、通过静态方法创建字符串对象
     NSString *string_7 = [[NSString alloc] initWithString:@"帅哥"];
     NSLog(@"%@",string_7);
     NSString *string_8 = [[NSString alloc]initWithUTF8String:str];
     NSLog(@"%@",string_8);
     NSString *string_9 = [[NSString alloc] initWithFormat:@"i love %@",@"iOS" ];
     NSLog(@"%@",string_9);
     
     //6. 从文件读取字符串:initWithContentsOfFile:
     NSString *path = @"/Users/student/Desktop/test.m"; //文件路径
     NSString *astring = [[NSString alloc] initWithContentsOfFile:path];
     NSLog(@"astring:%@",astring);
    
    
    // C字符串 --> OC字符串
    NSString *s4 = [[NSString alloc] initWithUTF8String:"jack"];
    // OC字符串 --> C字符串
    const char *cs = [s4 UTF8String];
//----------------比较两个字符串----------------
     //c语言中比较两个字符串
     char string[] = "iOS";
     char string1[] = "安卓";
     if (strcmp(string,string1)>0) {
     NSLog(@"1");
     }
     
     //1. isEqualToString方法 判断两个字符串是否相等 相等返回 1 不等返回 0
     BOOL result = [ string_9 isEqualToString: @"i love iOS"];
     NSLog(@"%i",result);
     
     
     //2. compare 方法(compare:返回的三种值 分别是-1,0,1)
     BOOL result_1 = [string_5 compare:string_9];//相同返回0 ，不同返回 1
     NSLog(@"%i",result_1);
     
     //NSOrderedSame 判断两者内容是否相同
     BOOL result_2 = [string_5 compare:string_9] == NSOrderedSame;//相同为1,不同为0
     NSLog(@"%i",result_2);
     
     //NSOrderedAscending 判断两对象值的大小(按字母顺序进行比较,result_1小于result_2 为真)
     BOOL result_3 = [@"ab" compare:@"b"] ==NSOrderedAscending ;
     NSLog(@"%i",result_3);//1小于2返回1 ，
     
     //NSOrderedDescending 判断两对象值的大小(按字母顺序进行比较,result_1大于result_2为真)
     BOOL result_4 = [@"ab" compare:@"b"] ==NSOrderedDescending ;
     NSLog(@"%i",result_4);//1大于2返回1
     
     //3. 不考虑大小写比较字符串
     //与不区分大小写仅仅是方法名不同
     BOOL result_5 = [@"ab" caseInsensitiveCompare:@"b"] ==NSOrderedAscending ;
     NSLog(@"%i",result_5);//1小于2返回1
     
//----------------改变字符串的大小写----------------
     
     //1. uppercaseString 小写转大写 （原字符串内容不改变）
     NSString *string_10 = [string_9 uppercaseString];
     NSLog(@"%@",string_10);
     
     //2. lowercaseString 大写转小写
     NSString *string_11 = [string_10 lowercaseString];
     NSLog(@"%@",string_11);
     
     //3. capitalizedString （单词 首字母大写 其余小写,其他字符保持不变
     NSLog(@"%@",[string_10 capitalizedString]);
     
//----------------搜索子串----------------
     NSString *string3 = @"i love iOS";
     NSString *string2 = @" love ";
     NSRange range = [string3 rangeOfString:string2];
     NSLog(@"length = %ld,location = %ld",range.length,range.location);
     
//----------------抽取子串 --substring--------------
     
     //1. -substringToIndex: 从字符串的开头一直截取到指定的位置,但不包括该位置的字符
     NSString *string4 = [string3 substringToIndex:6];
     NSLog(@"%@",string4);
     //2. -substringFromIndex: 从指定位置开始(包括指定位置的字符)提取,并包 括之后的全部字符 直到最后;
     NSLog(@"%@",[string3 substringFromIndex:6]);
     //3. -substringWithRange: //在指定范围内从字符串中截取子串
     NSLog(@"%@",[string3 substringWithRange:NSMakeRange(7, 7)]);
     
//------------判断字符串内是否还包含别的字符串(前缀,后缀)--has----------
     
     //01:检查字符串是否以另一个字符串开头- (BOOL) hasPrefix: (NSString *)aString; (判断前缀)
     NSLog(@"%i",[string3 hasPrefix:@"i  love"]);
     //02:检查字符串是否以另一个字符串结尾- (BOOL) hasSuffix: (NSString *)aString; (判断后缀)
     NSLog(@"%i",[string3 hasSuffix:@"iOS"]);
     
     
    //**************************************************
            // 二.NSMutableString
     // **********************************************
     
     //---------------给字符串分配预设空间大小----------------
     
     //stringWithCapacity:预设空间
     NSString *string5 = [NSMutableString stringWithCapacity:20];
     string5 = @"i love computer and my wife " ;
     
     //---------------增加字符串----------------
     //1. appendString: appendFormat: 追加,在后面追加字符串
     NSMutableString *string6 = [[NSMutableString alloc] initWithString:string5];
     [string6 appendString:string2];
     [string6 appendFormat:@"iOS"];
     NSLog(@"%@",string6);
     
     //2. -insertString: atIndex: 在指定位置插入字符串
     [string6 insertString:string2 atIndex:19];
     NSLog(@"%@",string6);
     
    
     //--------在已有字符串中按照所给出范围和长度删除字符------
     
     //deleteCharactersInRange: 在指定范围内删除字符串
     [string6 deleteCharactersInRange:NSMakeRange(0, 6)];
     NSLog(@"%@",string6);
     
     //--------修改字符串------
     
     //-setString: 修改字符串
     [string6 setString:string3];
     NSLog(@"%@",string6);
     
     //--------在指定范围内,替换的原有的字符------
     
     // replaceCharactersInRange: withString: 替换
     [string6 replaceCharactersInRange:NSMakeRange(0,1) withString:@"iOS is my love"];
     NSLog(@"%@",string6);
    
    NSRange range4 = [@"mrchen" rangeOfString:@"chen"];
    NSLog(@"%lu--%li",range4.length,range4.location);
    
    NSString *s = [@"mr" stringByAppendingString:@"chen"];
    NSLog(@"%@",s);
    
    //字符串导出
    [@"chen jingbaoying" writeToFile:@"/Users/student/Desktop/my.txt" atomically:YES encoding:NSUTF8StringEncoding error:Nil];//会替换原来的my.txt
    NSURL *url = [NSURL fileURLWithPath:@"/Users/student/Desktop/my.txt"];
    [@"iOS love"  writeToURL:url atomically:YES encoding:NSUTF8StringEncoding error:nil];//****************************************