NSString *str1 = @"BeiJing";     NSString *str2 = @"beijing";          //全部转为大写     NSLog(@"%@",[str1 uppercaseString]);          //全部转为小写     NSLog(@"%@",[str1 lowercaseString]);          //首字母大写     NSLog(@"%@",[str1 capitalizedString]);          //比较两个字符串内容是否相同     BOOL b =[str1 isEqualToString:str2];          //两个字符串内容比较     //NSOrderedAscending    右边 > 左边     //NSOrderedSame         内容相同     //NSOrderedDescending   左边 > 右边     NSComparisonResult result = [str1 compare:str2];     if (result == NSOrderedAscending) {         NSLog(@"右边 > 左边");     }else if(result == NSOrderedSame){         NSLog(@"内容相同");     }else if (result == NSOrderedDescending){         NSLog(@"左边 > 右边");     }          //忽略大小写进行比较，返回值与compare一样     result = [str1 caseInsensitiveCompare:str2];     if (result == NSOrderedAscending) {         NSLog(@"右边 > 左边");     }else if(result == NSOrderedSame){         NSLog(@"内容相同");     }else if (result == NSOrderedDescending){         NSLog(@"左边 > 右边");     }          //判断字符串是否以指定字符串开头     [str1 hasPrefix:@"aaa"];     //判断字符串是否以指定字符串结尾     [str1 hasSuffix:@"aaa"];          //判断字符串是否包含指定字符串，返回位置和长度     NSRange range = [@"123456" rangeOfString:@"456"];     NSLog(@"%@", NSStringFromRange(range));          //反向搜索     range = [@"123456456qweasasd456" rangeOfString:@"456" options:NSBackwardsSearch];     NSLog(@"%@",NSStringFromRange(range));          //指定范围进行搜索     range = NSMakeRange(0, 9);     range = [@"123456456qweasasd456" rangeOfString:@"456" options:NSBackwardsSearch range:range];     NSLog(@"%@",NSStringFromRange(range));  <pre name="code" class="cpp">//字符串的截取          NSString *str = @"123456789";          NSLog(@"%@",[str substringFromIndex:3]);          NSLog(@"%@",[str substringToIndex:6]);          NSLog(@"%@",[str substringWithRange:NSMakeRange(3, 3)]);                    //用指定字符串分割字符串，返回一个数组          NSArray *array = [@"1,2,3,4,5,6" componentsSeparatedByString:@","];          NSLog(@"%@",array);                    //将数组中的字符串组合成一个文件路径          NSMutableArray *components = [NSMutableArray array];          [components addObject:@"Users"];          [components addObject:@"CentralPerk"];          [components addObject:@"Desktop"];          NSString *path = [NSString pathWithComponents:components];          NSLog(@"%@",path);  //Users/CentralPerk/Desktop                    //将一个路径分割成一个数组          NSArray *array1 = [path pathComponents];          NSLog(@"%@",array1);                    //判断是否为绝对路径(依据：是否以‘/‘开始)          path = @"/Users/CentralPerk/Desktop";          NSLog(@"%i",[path isAbsolutePath]);                    //获取最后一个目录          NSLog(@"%@",[path lastPathComponent]);                    //删除最后一个目录          NSLog(@"%@",[path stringByDeletingLastPathComponent]);                    //拼接一个目录          NSLog(@"%@",[path stringByAppendingPathComponent:@"aaa"]);   ///Users/CentralPerk/Desktop/aaa          NSLog(@"%@",[path stringByAppendingString:@"aaa"]);      ///Users/CentralPerk/Desktopaaa          NSLog(@"%@",[path stringByAppendingFormat:@"%@%@",@"b",@"c"]);  ///Users/CentralPerk/Desktopbc                    //拓展名出来          //获取拓展名,不带.          NSString *str2 = @"Users/CentralPerk/Desktop/test.txt";          NSLog(@"%@",[str2 pathExtension]);          //添加拓展名,不需要带.          NSLog(@"%@",[str2 stringByAppendingPathExtension:@"mp3"]);          //删除拓展名,带.一块删除          NSLog(@"%@",[str2 stringByDeletingPathExtension]);                    //字符串转为 int double float          NSString *str3 = @"123";          NSLog(@"%i",[str3 intValue]);          NSLog(@"%zi",[str3 length]);                    //取出指定位置的字符          unichar c = [str3 characterAtIndex:2];          NSLog(@"%c",c);                    //转为C语言的字符串          const char *s = [str3 UTF8String];          NSLog(@"%s",s);  </pre><br><br>