截取2个指定字符串中的字符串

例如：

NSString *string = @"abavavasdsvx,as.dsf/,.[abcdefghijklmn]dgdfg";

NSRange start = [string rangeOfString:@"["];

NSRange end = [string rangeOfString:@"]"];

NSString *sub = [string substringWithRange:NSMakeRange(start.location, end.location-start.location+1)];

NSLog(@"sub=%@",sub);

控制台就输出:[abcdefghijklmn]