1、 创建常量字符串
NSString *astring = @"This is a String!";
2、 创建空字符串，给予赋值
NSString *astring = [[NSString alloc] init];
astring = @"This is a String!";
NSLog(@"astring:%@",astring);
3、 在以上方法中，提升速度：initWithString方法
NSString *astring = [[NSString alloc] initWithString:@"This is a String!"];
NSLog(@"astring: %@", astring);
4、 用标准c创建字符串:initWithCString方法
char *Cstring = "This is a String!";
NSString *astring = [[NSString alloc] initWithCString:Cstring];
NSLog(@"astring:%@",astring);
5、创建格式化字符串:占位符（由一个%加一个字符组成）
int i = 1;
int j = 2;
NSString *astring = [[NSString alloc] initWithString:[NSString stringWithFormat:@"%d.This is %d string!",i,j]];
NSLog(@"astring:%@",astring);
6、 创建临时字符串
NSString *astring;
astring = [NSString stringWithCString:"This is a temporary string"];
NSLog(@"astring:%@",astring);
7、 从文件创建字符串
NSString *path = [[NSBundle mainBundle] pathForResource:@"astring.text"ofType:nil];
NSString *astring = [[NSString alloc] initWithContentsOfFile:path];
NSLog(@"astring:%@",astring);
8、用字符串创建字符串，并写入到文件
NSString *astring = [[NSString alloc] initWithString:@"This is a String!"];
NSLog(@"astring:%@",astring);
NSString *path = @"astring.text";
[astring writeToFile:path atomically:YES];
注：此路径path只只是示意，真实路径并非如此
9、用C比较:strcmp函数
char string1[] = "string!";
char string2[] = "string!";
if(strcmp(string1, string2) == 0)
{
NSLog(@"1");
}
10、isEqualToString方法
NSString *astring01 = @"This is a String!";
NSString *astring02 = @"This is a String!";
BOOL result = [astring01 isEqualToString:astring02];
NSLog(@"result:%d",result);
11、compare方法(comparer返回的三种值)
NSString *astring01 = @"This is a String!";
NSString *astring02 = @"This is a String!";
BOOL result = [astring01 compare:astring02] == NSOrderedSame; //NSOrderedSame判断两者内容是否相同
NSLog(@"result:%d",result);
//
NSString *astring01 = @"This is a String!";
NSString *astring02 = @"this is a String!";
BOOL result = [astring01 compare:astring02] == NSOrderedAscending; //NSOrderedAscending判断两对象值的大小(按字母顺序进行比较，astring02大于astring01为真)
NSLog(@"result:%d",result);
//
NSString *astring01 = @"this is a String!";
NSString *astring02 = @"This is a String!";
BOOL result = [astring01 compare:astring02] == NSOrderedDescending; //NSOrderedDescending判断两对象值的大小(按字母顺序进行比较，astring02小于astring01为真)
NSLog(@"result:%d",result);
12 、-rangeOfString: //查找字符串某处是否包含其它字符串
NSString *string1 = @"This is a string";
NSString *string2 = @"string";
NSRange range = [string1 rangeOfString:string2];
int location = range.location;
int leight = range.length;
NSString *astring = [[NSString alloc] initWithString:[NSString stringWithFormat:@"Location:%i,Leight:%i",location,leight]];
NSLog(@"astring:%@",astring);
13、-substringToIndex: 从字符串的开头一直截取到指定的位置，但不包括该位置的字符
NSString *string1 = @"This is a string";
NSString *string2 = [string1 substringToIndex:3];
NSLog(@"string2:%@",string2);
14、-substringFromIndex: 以指定位置开始（包括指定位置的字符），并包括之后的全部字符
NSString *string1 = @"This is a string";
NSString *string2 = [string1 substringFromIndex:3];
NSLog(@"string2:%@",string2);
15、-substringWithRange: //按照所给出的位置，长度，任意地从字符串中截取子串
NSString *string1 = @"This is a string";
NSString *string2 = [string1 substringWithRange:NSMakeRange(0, 4)];
NSLog(@"string2:%@",string2);
16、-appendString: and -appendFormat: //把一个字符串接在另一个字符串的末尾
NSMutableString *String1 = [[NSMutableString alloc] initWithString:@"This is a NSMutableString"];
[String1 appendString:@", I will be adding some character"];
[String1 appendFormat:[NSString stringWithFormat:@", I will be adding some character"]];
NSLog(@"String1:%@",String1);
17、-insertString: atIndex: //在指定位置插入字符串
NSMutableString *String1 = [[NSMutableString alloc] initWithString:@"This is a NSMutableString"];
[String1 insertString:@"Hi! " atIndex:0];
NSLog(@"String1:%@",String1);
18、-replaceCharactersInRange: withString: //用指定字符串替换字符串中某指定位置、长度的字符串
NSMutableString *String1 = [[NSMutableString alloc] initWithString:@"This is a NSMutableString"];
[String1 replaceCharactersInRange:NSMakeRange(0, 4) withString:@"That"];
NSLog(@"String1:%@",String1);
19、componentsSeparatedByString://字符串截取
NSString *img = @"http://10.0.0.200:8081/rating/s/51/99/142863354169684.jpg,http://10.0.0.200:8081/rating/s/19/31/142863354191210.jpg,http://10.0.0.200:8081/rating/s/61/31/142863354123029.jpg,http://10.0.0.200:8081/rating/s/27/94/142863354177664.jpg,http://10.0.0.200:8081/rating/s/67/20/142863354133084.jpg";
NSArray *imgs = [img componentsSeparatedByString:@","];
NSString *url = [imgs objectAtIndex:2];
NSLog(@"\n 第三张图片地址是： %@", url);