OBJ-C

1.直接赋值

NSString *name = @"Starain";

2.用已经存在的字符串进行初始化

NSString *name2 = [NSString stringWithString:name];

或者NSString *name3 = [[NSString alloc]initWith String:name];

3.格式化字符串

int age = 20;

NSString *msg =[NSString stringWithFormat:@"name = %@, age = %d",name, age];

4.使用C语言字符串来初始化

NSString *str = [NSString stringWithCString:"C String" ,NSUTF8StringEncoding];

5.求字符串长度

NSString *str1 = @"Starain";

NSUInteger len = [str1 length];

NSLog(@"%lu",(unsignedlong)len);

6.特定位置字符（0开始）

char c1 = [str characterAtIndex:n]；

NSLog(@"%c",c1);

第6个位置，就是n=5时。

7.NSString 和NSData转换

常用于客户端项目获取网络数据

①NSString *str3 = @"hello world";

NSData *data = [str dataUsingEncoding:NSUTF8StringEncoding];

NSLog(@"%@",data);

②NSString *temp = [[NSString alloc]initWithData:data encoding:NSUTF8StringEncoding];

NSLof(@"%@",temp);

8.写文件操作

NNString *str = @"要写的内容";

NSString *path = @"/usr/starain/test.txt";//目录，如果没有可自行创建

BOOL result = [str writeToFile:path atomically:YES encoding:NSUTF8StringEncoding error:nil];//atomically表示是否有临时文件

NSLog(@"%d",result);

9.读文件操作

NSString *newstr = [NSString stringWithContensOfFile:path encoding:NSUTF8StringEncoding error:nil];

NSLog(@"%@",newstr);

10.字符串中取字符

①NSString *substr1 = [strm subStringToIndex:5];//从头开始取5个字符，取到第6个

NSLog(@"%@",substr1);

②NSString *substr2 = [strm subStringFromIndex:6];//从第7个字符取到末尾

NSLog(@"%@",substr2);

③NSRange r = NSMakeRange(2,3);//从第（2+1）个开始取3个

NSString *substr3 = [strm subStringWithRange:r];

NSLog(@"%@",substr3);

 11.类型转换

NSString *age = @"test";

int age1 = [age intvalue];

NSString *PI = @"3.1415";

float PI2 = [PI floatvalue];