Question

I have a function which sends a command over serial, then receives a response of unknown size. Using

(ioctl(fd_, FIONREAD, &bytes_in_buffer);

I determine how much memory I need to allocate for my read.

//This code calls the function below
unsigned char CheckRefresh[] = {254, 124, 0};
unsigned char * response;
unsigned int size;
relay_board->SendCustomCommand(CheckRefresh, 3, &response, size);

ErrorCode SendCustomCommand(unsigned char * command, unsigned int command_size, unsigned char **response, unsigned int &response_size)
{
  //Send the command
  write(fd_, command, command_size);

  // ... Omitting Polling Code to Get correct number of bytes ...
  (ioctl(fd_, FIONREAD, &bytes_in_buffer);

  //Now getting the response
  response_size = (unsigned int)bytes_in_buffer;
  (*response) = new unsigned char(response_size);
  if(read(fd_, *response, response_size) < 0)
  {
    std::cout << "[ProXRSerial] SendCustomCommand: Read failed... -- Errno: " << errno << std::endl;
    return Failed;
  };
  return Success;
}

I believe this is corrupting my stack, as my next function call breaks at

unsigned char * command = new unsigned char(3);

with the following:

sYSMALLOc: Assertion `(old_top == (((mbinptr) (((char *) &((av)->bins[((1) - 1) * 2])) -
__builtin_offsetof (struct malloc_chunk, fd)))) && old_size == 0) || ((unsigned long) 
(old_size) >= (unsigned long)((((__builtin_offsetof (struct malloc_chunk, fd_nextsize))+((2 
* (sizeof(size_t))) - 1)) & ~((2 * (sizeof(size_t))) - 1))) && ((old_top)->size & 0x1) && 
((unsigned long)old_end & pagemask) == 0)' failed.

Could anyone offer some advice? I am at a loss, I thought passing the double pointer like that would allow me to allocate memory for the user…

Thank you in advance.

Answer 1

The line

(*response) = new unsigned char(response_size);

should read

(*response) = new unsigned char[response_size];

Your version allocates one unsigned character, and initializes it with the value response_size.