OC-NSString

Foundation/NSString.h
String constants are called from the beginning of execution of the program to the termination of the programreleaseNeither method nor garbage collection can release
NSStringRepresents an immutable string object It cannot be changed by additions and deletions
String used internallyUnicode编码
NSStringin a cluster-like manner(class cluster)Think of it as a factory class

定义方式

 NSString *a = @"abc";

The compiler will concatenate strings separated by spaces

拼接字符串

stringByAppendingFormat Multiple strings can be concatenated

       NSString *a = @"abc";
        NSString *c = @"zzzz";
        NSString *b = [a stringByAppendingFormat:@"第一个参数: %@ 第二个参数%@",@12,c];//abc第一个参数: 12 第二个参数zzzz

-(NSUInteger)length 获取长度

返回字符串中UnicodeThe number of encoded characters The return value of this function cannot be used to calculate the number of bytes required Because it returns the number of characters But you don't know how many bytes a character occupies

componentsJoinedByString Concatenate strings by specifying symbols

NSArray* array = @[@"a",@"b",@"c"];
NSString *string = [array componentsJoinedByString:@"-"];
NSLog(@"%@",string);

查找字符串

rangeOfString //从stringFind the string inside and return itrange形式变量

找到了 就返回{location,length}
没找到 返回{NSNotFound,0}

NSString *string = @"0123456789abc";
NSRange range = [string rangeOfString:@"34"];
NSLog(@"@",NSStringFromRange(range));//{3,2} 第三个位置 两个字符
NSRange range = [string rangeOfString:@"Ab" options:NSCaseInsensitiveSerch];//添加参数 This is case sensitive

分割字符串

componentsSeparatedByString Split by the specified symbol

NSString *string = @"sbcd-efht-defagfds";
NSArray *array = [string componentsSeparatedByString:@"-"];
NSLog(@"array = %@",array);//array = (sbcd,efht,defagfds)

substringWithRange 通过range分割字符串

NSString *string = @"0123456789abc"
NSRange range  ={
    3,8};
NSString *newString = [string substringWithRange:range];//从第3Bits start to take eight 3456789a

删除字符串

stringByTrimmingCharactersInSet: 删除特殊符号 Commonly used spaces

NSString * string = @" abcd ";
string = [string stringByTrimmingCharactersInSet:NSCharacterSet whitespaceCharacterSet];//abcd whitespaceCharacterSet是空格

替换字符串

stringByReplacingOccurrencesOfString:withString: 将指定字符串a替换成指定字符串b

NSSstring string = @“lixun”;
NSString *newString = [string stringByReplacingOccurrencesOfString:@"li"withString:@“liu”];将li字符串替换成liu

stringByReplacingCharactersInRange:withString:

NSString * string = @“aaaaaaannnnnnn”;
NSRange range = {4,3};
string = [string stringByReplacingCharactersInRange:range withString:@“qqqqqqqq”];//Indicates that the fourth position will be3个字符替换成qqqqqqqqq //aaaqqqqqqqqannnnnnn

字符串比较

NSString *string1 = @“abc”;
NSString *string2 = @"ABC";
NSComparisonResult rs = [string1 compare:string2];
if(rs == NSOrderedAscending){
    NSLog(@"string1<string2")};
else if(rs == NSOrderedSame){
    NSLog(@"string1 = string2")};
else{
    NSLog(@"string1>string2")}; 

关于UTF-8的解码方式

因为ASCIISimply using a byte to represent a character causes the text of many countries to be unable to be represented
所以发明了unicode编码 unicodeThere are several ways of encoding UTF-8 UTF-16 UTF-32
UTF-8The biggest feature is the variable length 用1-4个字节表示
1.When only represented by a single byte 第一位设为0 后面7位对应这个字符的Unicode码
2.对于需要使用Ncharacter to represent（N>1）第一个字节的前N位都设为1 第N+1位设为0
The first two bits of the remaining bytes are set10
So if the first one is0It means that one byte corresponds to one character 如果第一位是1 Then see how many consecutive1It indicates how many bytes a character occupies

0xxxxxxx
110xxxxx 10xxxxxx
1110xxxx 10xxxxxx 10xxxxxx
11110xxx 10xxxxxx 10xxxxxx 10xxxxxx