1、字符串的截取

//1.截取字符串
NSString *string =@"123456d890";
NSString *str1 = [string substringToIndex:5];//截取掉下标5之前的字符串
NSLog(@"截取的值为：%@",str1);
 NSString *str2 = [string substringFromIndex:3];//截取掉下标3之后的字符串
NSLog(@"截取的值为：%@",str2);

2、匹配字符串

从字符串(sd是sfsfsAdfsdf)中查找(匹配)字符串(Ad)

//2.匹配字符串
NSString *string =@"sd是sfsfsAdfsdf";
NSRange range = [string rangeOfString:@"Ad"];//匹配得到的下标
NSLog(@"rang:%@",NSStringFromRange(range));
string = [string substringWithRange:range];//截取范围内的字符串
NSLog(@"截取的值为：%@",string);

3、字符串分割

根据字符串中的某个字符(A)来分割字符串

//3.分隔字符串
NSString *string =@"sdfsfsfsAdfsdf";
 NSArray *array = [string componentsSeparatedByString:@"A"]; //从字符A中分隔成2个元素的数组
NSLog(@"array:%@",array); //结果是adfsfsfs和dfsdf

4、NSString的反转

如abcdefg反转后为gfedcba

NSString * str = @"beijing huan ying nin";
unsigned long len;
len = [str length];
unichar a[len];
for(int i = 0; i < len; i++)
{
unichar c = [str characterAtIndex:len-i-1];
a[i] = c;
}
NSString *str1=[NSString stringWithCharacters:a length:len];
NSLog(@"--- 反转之后的字符串 ----%@",str1);

5、数组拼接成字符串

NSString *string = [array componentsJoinedByString:@","];//--分隔符

6、汉字转拼音，小写转大写，大写转小写

NSString *tempStr = @"你好";
//转成可变字符串 
NSMutableString *tempStr1 = [NSMutableString stringWithString:tempStr];
//先转换为带声调的拼音
CFStringTransform((CFMutableStringRef)tempStr1, NULL, kCFStringTransformToLatin, false);
//再转换为不带声调的拼音 
CFStringTransform((CFMutableStringRef)tempStr1, NULL, kCFStringTransformStripDiacritics, false);
NSLog(@"汉字转拼音：tempStr1 == %@", tempStr1);  // ni hao
tempStr1 = (NSMutableString *)tempStr1.uppercaseString;
NSLog(@"小写转大写：tempStr1 == %@", tempStr1);  // NI HAO
tempStr1 = (NSMutableString *)tempStr1.lowercaseString;
NSLog(@"大写转小写：tempStr1 == %@", tempStr1);  // ni hao

7、字符串类型判断

#define ENGLISH @"[a-zA-Z]"  // 英文
#define CHINESE @"[\u4e00-\u9fa5]"  // 汉字
#define INTSTR @"[0-9]"  // 数字
#define SMALLLETTER @"[a-z]"  // 小写字母
#define CAPITALLETTER @"[A-Z]"  // 大写字母

/*!
* @brief 字符串判断
* @param str 字符串，strRegex 正则表达式
* @return 返回YES或NO
*/
- (BOOL)typeJudgeWithStr:(NSString *) str withType:(NSString *) strRegex
{
    NSPredicate *strPredicate = [NSPredicate predicateWithFormat:@"SELF MATCHES %@", strRegex];
    return [strPredicate evaluateWithObject:str];
}

8、字典转JSON字符串，JSON字符串转字典

/*!
* @brief 把格式化的JSON格式的字符串转换成字典
* @param jsonString JSON格式的字符串
* @return 返回字典
*/
+ (NSDictionary *)dictionaryWithJsonString:(NSString *)jsonString {
if (jsonString == nil) {
  return nil;
} 
NSData *jsonData = [jsonString dataUsingEncoding:NSUTF8StringEncoding];
NSError *err;
NSDictionary *dic = [NSJSONSerialization JSONObjectWithData:jsonData
options:NSJSONReadingMutableContainers
error:&err];
if(err) {
NSLog(@"json解析失败：%@",err);
return nil;
}
return dic;
}
// 字典转json字符串
+ (NSString*)dictionaryToJson:(NSDictionary *)dic
{
NSError *parseError = nil;
NSData *jsonData = [NSJSONSerialization dataWithJSONObject:dic options:NSJSONWritingPrettyPrinted error:&parseError];
return [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];
}

9、字符串（大、小写）

// 把字符串全部转化为小写
NSString  *str =@"AAaaBBbb";
NSString * str = [str lowercaseString];

// 把字符串全部转化为大写
NSString * str = [str uppercaseString];

//开头大写，其余小写
NSString * str =[str capitalizedString];

链接：https://www.jianshu.com/p/d17885464698
链接：https://www.cnblogs.com/somebodywx/p/5724892.html
链接：https://www.jianshu.com/p/c8702df7d6ce
链接：https://www.jianshu.com/p/5b418818dbce