CODEWITHSUNDEEP
c++winapibinaryhex
user3048644
user3048644

Reputation: 93

how to insert hex value inside an hex char array

I have a loop let say from 1 to 32. 1 to 32 are decimal in this case. I have to insert the hex value of 1 to 32 in an unsigned char array and then perform send. My code looks like this

char hex[3];
unsigned char hexunsigned[3];
int dec; 
int i=0;
do
{
    // this is the unsigned char array , i have to insert at 4th pos.  
   unsigned char writebuffer[8] ={0x01, 0x05, 0x00, 0x20, 0xFF, 0x00, 0x00, 0x00};

   // to place the hex value of each point on writeBuffer[3]
   dec=i+1;
   decimal_hex(dec,hex); //this function returns hex value of corresponding i value.
   memcpy(hexunsigned,hex,sizeof(hexunsigned)); //converting char to unsigned char

   writebuffer[3]= hexunsigned; //shows the error cannot convert from 'unsigned char [3]' to 'unsigned char'

   unsigned short int crc = CRC16(writebuffer, 6); // Calculates the CRC16 of all 8 bytes
   writebuffer[6] = ((unsigned char*) &crc)[1];
   writebuffer[7] = ((unsigned char*) &crc)[0];

   serialObj.send(writebuffer, 8);
   //send another packet only after getting the response
   DWORD nBytesRead = serialObj.Read(inBuffer, sizeof(inBuffer));
   i++;

}while(nBytesRead!=0 && i<32);

so, the line

writebuffer[3]= hexunsigned;

shows the error as cannot convert from 'unsigned char [3]' to 'unsigned char'.
how to insert hex unsigned in writebuffer array.

when 

char hex[3];
int dec;
dec=i+1;
decimal_hex(dec,hex); 
memcpy(writebuffer+3, hex, sizeof(writebuffer+3));

is used , it is translating 01(dec) as 31.

I have tried the below code also , it is also translating 01(dec) as 31. 

sprintf(hex, "%X", dec); 
memcpy(writebuffer+3, hex, sizeof(writebuffer+3));

I think it is treating '1' received at hex variable as ascii and sending hex value of character '1' as 31.

The send function is below:

void serial::send(unsigned char data[], DWORD noOfByte)
{
    DWORD dwBytesWrite;
    WriteFile(serialHandle, data, noOfByte, &dwBytesWrite, NULL);
}

Upvotes: 0

Views: 3229

Answers (3)

Daniel King
Daniel King

Reputation: 405

You can merge the two lines

memcpy(hexunsigned,hex,sizeof(hexunsigned)); //converting char to unsigned char

writebuffer[3]= hexunsigned;

into one:

memcpy(writebuffer+3, hex, 3);</strike>

and the temporary hexunsigned is redundant
--------------------Update line--------------------
Actually when we say hex encoding, we want to use two bytes to represent an original byte, for example 0x33 30 // '3' '0' represents 0x30
So in you case 0x01~0x20 should be represented as 0x00 01 to 0x02 00, if you want to use sprintf to convert from dec to hex, you can use as this:

sprintf(hex, "%02X", dec); 
memcpy(writebuffer+3, hex, 2);

And your output will be like this "01 05 00 30 31 00 00 00" for i=1 without CRC16 considered.

Upvotes: 1

WKPlus
WKPlus

Reputation: 7255

hexunsigned must be a unsigned char array, and writebuffer[3] is a unsigned char.

You can not assign a unsigned char to a unsigned char array.

If you want to copy hexunsigned to writebuffer[3] address, use memcpy.

Upvotes: 0

ScottMcP-MVP
ScottMcP-MVP

Reputation: 10415

You will have to use memcpy to copy a three char array.

Upvotes: 0

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