day4---字符串详解

一、字符串的创建与转换
1.通过对象方法创建
1)通过一个字符串去创建新的字符串
NSString *str2 = [[NSString alloc] initWithString:str1];
2)把C字符串转换成OC字符串
NSString *str3 = [[NSString alloc] initWithUTF8String:"WHiOS1603"];
3)【重点】
通过格式符创建(拼接)字符串
NSString *str4 = [[NSString alloc] initWithFormat:@"%d-%.2f-%c-%s", 100,3.1415926,'Q',"QF"];

2.通过类方法创建字符串对象
1)通过一个字符串去创建新的字符串
    NSString *str2 = [[NSString stringWithString:str1];
2)把C字符串转换成OC字符串
    NSString *str3 = [NSString stringWithUTF8String:"WHiOS1603"];
3)【重点】
    通过格式符创建(拼接)字符串
NSString *str4 = [NSString stringWithFormat:@"%d-%.2f-%c-%s",   100,3.1415926,'Q',"QF"];



3.把OC字符串转换成基础数据类型
1)转换成int类型
    int a = str.intValue;       用%d打印

2)转换成long类型  NSInteger 32->int  64->long
    NSInteger integer = str.intValue    32位用%d打印,64位用%ld打印

3)转换成BOOL类型
    BOOL bl = str.boolValue;         用%d打印
    
    
4)把OC字符串转换成C字符串
    const char *s = [str UTF8String];      用%s打印


5)返回字符串的长度
     NSUInteger len = [str length];    32->unsigned int 64->unsigned long
    
6)取出字符串中的单个字符,unichar就代表C语言中的char
    unichar c = [str characterAtIndex:5];

二、字符串的查找和提取
1)字符串查找
NSRange range = [str1 rangeOfString:subStr1];
NSLog(@"location:%ld length:%ld", range.location,range.length);
//NSRange是一个结构体,包含了location和length两部分
//location子串在父串中的起始位置 length子串的长度

2)字符串提取
    //从某个位置开始一直截取到某个字符串结尾

NSString *subStr2 = [str1 substringFromIndex:8]; //8代表从下标为8的位置开始截取

    //从开始位置截取,截取到某个位置(注:但不包含截取到的这个位置)
    NSString *subStr3 = [str1 substringToIndex:4];
    
    //截取一个字符串中的某个字符串 

// NSRange rg = NSMakeRange(4, 6);
NSRange rg = {4,6};
NSString *subStr4 = [str1 substringWithRange:rg];

三、字符串大小比较 和 大小写转换
1)判断两个字符串是否相等(非常重要
BOOL bl = [str1 isEqualToString:str2]; //返回的是bool值,进行判断

2)比较两个字符串的大小
NSComparisonResult result = [str1 compare:str2]; //返回枚举,进行判断

    if (result == NSOrderedAscending) {
        NSLog(@"str1小于str2");
    }else if(result == NSOrderedSame){
        NSLog(@"str1等于str2");
    }else{
        NSLog(@"str1大于str2");
    }
    
3)不区分大小写比较两个字符串大小
NSComparisonResult result2 = [str1 caseInsensitiveCompare:str2];
    
    if (result2 == NSOrderedAscending) {
        NSLog(@"str1小于str2");
    }else if(result2 == NSOrderedSame){
        NSLog(@"str1等于str2");
    }else{
        NSLog(@"str1大于str2");
    }
    
4)字符大小写转换
            NSString *string = @"abcd123xyz";
    //转换常大写
    NSString *uppStr = [string uppercaseString];
    NSLog(@"string = %@", uppStr);
    
    //大写转小写
    NSString *lowStr = [uppStr lowercaseString];
    NSLog(@"loeStr = %@", lowStr);
    
    
    //首字母大写,其余全部小写
    NSString *capStr = [string capitalizedString];
    NSLog(@"capStr = %@", capStr);
    
    
5)判断字符串的前后缀
            NSString *string1 = @"qianfeng1603Class.txt";
    NSString *preStr = @"qian";
    NSString *suffStr = @".txt";
    
    //1.判断前缀
    BOOL rect1 = [string1 hasPrefix:preStr];
    if (rect1 ) {
        NSLog(@"是前缀");
    }else{
        NSLog(@"不是前缀");
    }
    
    //2.判断后缀
    BOOL rect2 = [string1 hasSuffix:suffStr];
    if (rect2) {
        NSLog(@"是后缀");
    }else{
        NSLog(@"不是后缀");
    }

6)字符串的各种拼接
    NSString *string2 = @"Hello,Girl!";
    NSString *newStr1 = [string2 stringByAppendingString:@" I Love You!!!"];
    NSLog(@"newStr1 = %@", newStr1);
    
    //2)格式符拼接

NSString *newStr2 = [string2 stringByAppendingFormat:@"%d,%@",999,@"玫瑰"];
NSLog(@"mewStr2 = %@", newStr2);

    //3)拼接路径(默认加上/)
    NSString *newStr3 = [string2 stringByAppendingPathComponent:@"love.ppt"];
    NSLog(@"newStr3 = %@",newStr3);

四、可变字符串
1)创建
创建一个空的字符串
NSMutableString *mStr1 =[[NSMutableString alloc] init];
NSMutableString *mStr2 =[NSMutableString string];

    创建一个预设大小的可变字符串
NSMutableString *mStr3 = [[NSMutableString alloc] initWithCapacity:20];
    NSMutableString *mStr4 = [NSMutableString stringWithCapacity:10];

    通过一个不可变字符串创建一个可变字符串
    NSString *str =@"今天学习字符串";
    NSMutableString *mStr5 = [[NSMutableString alloc] initWithString:str];
    NSMutableString *mStr6 = [NSMutableString stringWithString:str];
    
    
    
2)增
            //1.在指定的位置插入新的字符串
    [mStr6 insertString:@"我们" atIndex:2];
    NSLog(@"mStr6 = %@", mStr6);
    
    //2.在原来的字符串的基础上追加一个字符串
    [mStr6 appendString:@"-宝宝不开心"];
    NSLog(@"mStr6 = %@", mStr6);
    
    //3.在原来的字符串的基础上格式符追加
    [mStr6 appendFormat:@"%s"," NSMutableString"];
    NSLog(@"mStr6 = %@", mStr6);
    
    
3)删除
    //1.删除指定范围的字符串
    NSRange range ={6,3};
    [mStr6 deleteCharactersInRange:range];
    NSLog(@"mStr6 = %@", mStr6);
    
    
    
4)修改
    //1 替换掉指定范围的字符串
    NSRange range1 = {0,2};
    [mStr6 replaceCharactersInRange:range1 withString:@"现在"];
    NSLog(@"mStr6 = %@", mStr6);
    
    //2.直接用用一个新字符串全部替换掉原来的字符串
    NSString *newStr = @"一切都是浮云";
    [mStr6 setString:newStr];
    NSLog(@"mStr6 = %@", mStr6);

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