NSString字符串截取

1.截取字符串一部分 (substringWithRange:(NSRange*))

NSString *a = @"01234567890";

NSString *b = [a substringWithRange:NSMakeRange(0,2)];

b = "01"

2.字符串截取到第n位 （substringToIndex: n) (第n位不在截取范围内）

NSString *a = @"01234567890";

NSString *b = [a substringToIndex:5];

b = "01234"

3.字符串从第n位开始截取 （substringFromIndex: n）（第n位包括在截取范围内）

NSString *a = @"01234567890";

NSString *b = [a substringFromIndex:5];

b = "567890"

4.字符串按照要求删去 （deleteCharactersInRange:(NSRange*))

NSString *a = @"01234567890";

NSString *b = [a deleteCharactersInRange:NSMakeRange(1,4)];

b = "0567890"