OC - NSString

1.字符串的截取

字符串的截取用: 字符串 +substring..
如果开始就截取用from, 如果截取到用to。
截取的范围先rande{从哪，长度}

• 从索引开始截取

NSString *str = [@"123456" substringFromIndex:3];
str = @"456";

• 截取到索引

NSString *str = [@"123456" substringFromIndex:4];
str = @"1234";

• 截取的范围，长度

NSRange r={2,3};//截取的范围，长度
NSString *str =[@"123456" substringWithRange:r];
str8= @"345";

2.字符串的拼接

NSString  *str =[NSString stringWithFormat:@"%@%@",str1,str2];
NSString  *str = [str1 stringByAppendingString:str2];(比较好一点)
NSString  *str = [str stringByAppendingFormat:@"%@,%@",string1, string2]

3.字符串的比较

• 比较两个字符串是不是同一个东西

NSString *str01 =[NSString stringWithFormat:@"iphone"];
NSString *str02 =[NSString stringWithFormat:@"ipad"];
NSLog(@"str01的地址%p",str01); 0x656e6f68706965
NSLog(@"str02的地址%p",str02); 0x6461706945

• 判断地址是否相同用==判断(双等号)

if (str01==str02){
        NSLog(@"他俩是同一个字符串");
}else{
        NSLog(@"他俩不是同一个字符串");
}

• 判断字符串的内容是否相同

if ([str01 isEqualToString:str02]) {
        NSLog(@"他俩内容相同");
}else{
        NSLog(@"他俩内容不相同");
}

• 字符串的大小比较

NSComparisonResult CR =[str01 compare:str02];
if (CR==NSOrderedAscending) {
      NSLog(@"str02>str01");
 }else if (CR == NSOrderedSame){
      NSLog(@"str02=str01");
 } else{
      NSLog(@"str02<str01");
 }
结果 str02<str01

4.字符串大小写转换

NSString *str11 =@"Hello wORld";

• 改写成全部大写

NSString *ustr=[str11 uppercaseString];
结果 HELLO WORLD

• 改写成全部小写

NSString *ustr=[str11 lowercaseString];
结果 hello world

• 改写成首字母大写

NSString *ustr=[str11 capitalizedString];
结果 Hello World

5.判断字符串的开始和结束

NSString *str12 =@"ios-iphone";

• 开始

if ([str12 hasPrefix:@"io"]) {
        NSLog(@"YES");
}else{
        NSLog(@"NO");
}

• 结束

if ([str12 hasSuffix:@"io"]) {
        NSLog(@"YES");
}else{
        NSLog(@"NO");
}

6.字符串的替换

NSString *str =@"qwertyuiop";

NSString *str=[str stringByReplacingOccurrencesOfString:str withString:@"tyuio"];
str=tyuio

NSString *str15 =[str stringByReplacingCharactersInRange:NSMakeRange(4,5) withString:@"A"];
str15=qwerAp

7.可变字符串

NSMutableString继承与NSString

NSMutableString *mstr = [NSMutableString stringWithFormat:@"iphone"];

• 插入字符串

[mstr insertString:@"ipad" atIndex:3];
mstr =iphipadone

-追加字符串

mstr =iphoneipad
[mstr appendString:@"ipad"];
mstr =iphoneipadipad

-给定一个图片文件名,判断字符串中是否以“png”结尾,如果是就替换成“jpg”,如果 不是,就拼接”.jpg

 NSMutableString *str0=[NSMutableString stringWithFormat:@"001.png"];
    if ([str0  hasSuffix:@"001.png"]){ 
       //求字符串长度的方法 length
        [str0 replaceCharactersInRange:NSMakeRange(str0.length-3, 3) withString:@"jpg"];
    }else {
        [str0 appendString:@".jpg"];
    }
       str0=001.jpg