Thread: memcpy - part of array to specific position in different array

Hello,

I am trying to do a simple program like this. There is an input, which is a wide-char message and i should copy only some substrings of this message to the output. In the example below, the output should be input[4]+input[3..5]. So lets say for wcMessageIn='ABCDEFG' I should get wcMessageOut='DCDE'.

Code:

#define MSG_LENGTH 4096

static wchar_t *wcMessageIn;    
static wchar_t *wcMessageOut; 

int main(int argc, char *argv[])                 
{
  wcMessageIn = (wchar_t *)malloc(MSG_LENGTH * sizeof(wchar_t));
  wcMessageOut = (wchar_t *)malloc(MSG_LENGTH * sizeof(wchar_t));

  /* receive message and convert it to wcMessageIn using mbstowcs */
  /* lMsgWCharLen = mbstowcs(wcMessageIn, cMessage, MSG_LENGTH);  */

  /* copy 4th character on input to 1st character on output - THIS WORKS*/
  wcMessageOut[0] = wcMessageIn[3];
	
  /* append 3th to 5th character on input to output - THIS DOES NOT WORK */
  memcpy(wcMessageOut + 1*sizeof(wchar_t), wcMessageIn + 2*sizeof(wchar_t), 3*sizeof(wchar_t));
	
  /* do some cleanup here */
}

Can you please help me with the memcpy? In the real world, the messages will be long and I would be copying substrings of hundreds or thousands characters, so I would like to avoid doing it in a loop, char by char.

Something like...

Code:

memcpy(out,in + start_offset, total_len - end -start_offset);

Salem, thank you very much. That helped a lot!