Parse unsigned char[] to std::string

Question

I have a problem with parsing the contents of a char[]. It contains bytes, that can be formated as ASCII stings. The last two bytes however are CRC. Therefore I interpret everything but the last two entries in the array in hex to string:

std::ostringstream payload;
std::ostringstream crc;
payload << std::hex;
crc << std::hex;

// last two bytes are CRC
for (int i = 0; i < this->d_packetlen - 2; i++)
  {
  payload << static_cast<unsigned>(this->d_packet[i]);

     for (int j = i; j < this->d_packetlen; i++)
       {
         crc << static_cast<unsigned>(this->d_packet[j]);
       }
}
std::string payload_result = payload.str();
std::string crc_result = crc.str();

fprintf(d_new_fp, "%s, %s, %d, %d\n", payload_result.c_str(),
   crc_result.c_str(), this->d_lqi, this->d_lqi_sample_count);

This doesn't work, and I'm not sure why that is? Is there an easier way to cast unsinged chars to ASCII?

Best, Marius

Answer 1

This is an infinite loop:

for (int j = i; j < this->d_packetlen; i++)
{
   crc << static_cast<unsigned>(this->d_packet[j]);
}

In this loop, you are NOT incrementing j ; instead you're incrementing i . Maybe, that is the problem?

---

Also, the way you've described the problem, I think the correct solution is this:

for (int i = 0; i < this->d_packetlen - 2; i++)
{
  payload << static_cast<unsigned int>(this->d_packet[i]);
}
for (int j = this->d_packetlen - 2; j < this->d_packetlen; j++)
{
   crc << static_cast<unsigned int>(this->d_packet[j]);
}

That is the second loop should be outside the first loop.

Answer 2

I think the problem is that your nested loop increments i instead of j .

for (int i = 0; i < this->d_packetlen - 2; i++)
{
payload << static_cast<unsigned>(this->d_packet[i]);

     for (int j = i; j < this->d_packetlen; i++ /* <=== HERE */)
     {
         crc << static_cast<unsigned>(this->d_packet[j]);
     }
}