A readfile buffer passing

Question

This is probably trivial but I cannot get why I dont get the read back in my program. It seem to work fine for all the "complex stuff", and it says it has read 1 (character/byte), but I cannot get hold of it; it seems to be typ-matching problems (this is really weird the compiler g++ (i.e. gcc) btw ).

How I alter different variants of Buf (as pointer, char, char array, etc) I cannot get hold of the input.

SO below is now the stripped code and sync read version. Which also should compile.

#define WIN32_LEAN_AND_MEAN
#include <stdio.h>
#include <windows.h>
using namespace std;

//**********************************
//*******   M A I N  ****************
//**********************************

int main()    
{

HANDLE hComm;
int choice;

// non overlap test case (2nd last par = 0)

hComm = CreateFile( "COM4",  
                    GENERIC_READ | GENERIC_WRITE, 
                    0, 
                    NULL, 
                    OPEN_EXISTING,
                    0,
                    0);

if (hComm == INVALID_HANDLE_VALUE){
   // error opening port; abort
   printf("open error COM4\n");
   }
else
   printf("COM4 open");

printf("\n Hi, this is a UART attempt:"); scanf("%d", &choice);


// build the control block

DCB           dcb={0};


printf("******dcb******\n");

dcb.DCBlength = sizeof(dcb);

if ( !GetCommState(hComm, &dcb)) printf("Get DCB error");  // I dont think this should be needed ?


if ( ! BuildCommDCB( "4800,n,8,2" , &dcb ) ) {
    // error
    printf("COM4 buidDCB -- error\n");
    return(1);
    }


printf("****here*****\n");

// put the control block into action

if (! SetCommState( hComm, &dcb )  ){
    // error
    printf("COM4 setCommState -- error:%d \n",(int)GetLastError() );
    return(1);
    }

printf("seem successfull \n");


/*************************************READ non-ASYNC TESTING ************************************/
/********************************************************************************************/

char  Buf[1];

/* initiate waiting for reading on UART */

DWORD dwRead;

// Issue rea


if ( ! ReadFile(hComm, Buf, 1 , &dwRead, 0)) {
      // Error in communications; report it.
      printf("ReadFile --- error:%d",(int)GetLastError());
}
else {    
   // read completed
   printf("read <%d>---%o--- \n",(int)dwRead,Buf[0]);
}


return 0;
}  //*** end main ************************************

Answer 1

You are going to kick yourself: The problem is that the final printf (to display the value) should be:

  printf("--- immediate read <%d>---%o--- \n",(int)dwRead,Buf[0]);

Note the trailing [0] on Buf.

Alternatively, you could declare Buf as:

char Buf;

and then the call would be:

    if ( ! ReadFile(hComm, &Buf, 1, &dwRead, &osReader)) {

(with a & on Buf.)