"Different levels of indirection" compilation error

This is a discussion on "Different levels of indirection" compilation error within the C Programming forums, part of the General Programming Boards category; In converting an MS C (v6) program from Scalable SQL to the Btrieve API (BTRV function), I need to understand ...

  1. #1
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    "Different levels of indirection" compilation error

    In converting an MS C (v6) program from Scalable SQL to the Btrieve API (BTRV function), I need to understand the intricacies of pointers in order to resolve a "different levels of indirection" compilation error.

    The original program declared cursors and hence read in several records at a go (using xNew and xFetch). Relevant code, I hope, below...
    Code:
    #define N_FETCH  20
    #define NIBBLE   0x000F /* binary representation 0000000000001111  */
                            /* This half-byte is used to mask off all but the
                               four bits of interest in each conversion step.   */
    #define BYTE     0x00FF  /* binary representation 0000000011111111   */
    
    struct crdRec
    {   int  Recordlen;
         char  CrCustnum  [6];
    <snip>
         char CrFxfwddelex [7];
         char CrSgnfxfdlex [1];
    };
    struct i1bRec
    {   int  Recordlen;
         char  Custnum  [6];
    <snip>
         char Sgnfxfdlex [1];
         char Fxfwddelex [14];
    };
    struct  crdRec  crdVRec  [N_FETCH];
    struct  i1bRec   i1bVRec  [N_FETCH];
    int rind;
    char  hexbuf [5];
    char *inPtr, *outPtr;
    char hextab[] = { '0', '1', <snip> 'F' };
    char *byte2hex (unsigned char, char *);
    That is most of the relevant declarations. Here is some code.
    Code:
    /* code to select cursor of data*/
    status = xFetch (cursorID1, &bufLen, opt, &recCount, 
                                  &rejCount, (char *) crdVRec);
    if (status == 0 || status == 9)
    {
    /* total number of records selected  */
      t_recCount += recCount;
    
      for (rind = 0; rind < recCount; rind++)
      {
        i1bVRec[rind].Recordlen = sizeof(struct i1bRec) -2 ;
        strncpy (i1bVRec[rind].Custnum, crdVRec[rind].CrCustnum,  6);
    <snip>
    /* convert packed data field  */       
       inPtr = (char *) &crdVRec[rind].CrFxfwddelex ;
       outPtr = (char *) &i1bVRec[rind].Fxfwddelex ;
    
       for (i = 0;  i < 7 ; ++i)
         {
           strcpy (outPtr, byte2hex (*inPtr++, hexbuf));
           outPtr  += 2;
          }
    It is on the strcpy, on my converted version, where it gives the compilation error. I haven't tried compiling this original code yet; I'll do that shortly, it may not compile itself for all I know. I've had that happen before!

    For info, the byte2hex function:
    Code:
    /* =========================  byte2hex () ================ */
    /*   Convert a byte to a string representation of its hexadecimal value     */
    /*   The function byte2hex() , converts a byte-sized(8-byt) quantity to     */
    /*   hexadecimal.                                                           */
    /*   The hextab array is a conversion lookup table. It uses a number in     */
    /*   the range of 0 through 15 as an index into the table, where the        */
    /*   corresponding character constant (number or letter) is found.          */
    /* =================================================== */
    
    char *byte2hex (data, buf)
    unsigned char data;
    char *buf;
    {
       char *cp;
       unsigned int d;
    
    
       d = data & BYTE;  /* turn off the 4 high order bits */
       cp = buf;         /* assign pointer to output buffer */
    
       /* Right-shift operations are used to pull the needed bits into the
          correct position for convertion to a hexadecimal digit.   */
       /* move 1st 4 low order bits to right and turn off all other bits */
       *cp++ = hextab [(d >> 4) & NIBBLE];
    
       /* turn off last 4 low order bits */
       *cp++ = hextab [d & NIBBLE];
    
       *cp = '\0';
       return (buf);
    }
    /* End of byte2hex */
    Now for my converted version, using the Btrieve API. I am not using a cursor, hence only reading one record at a time. I am not using crdVRec and i1bVRec,
    but am doing the following:
    Code:
    struct  crdRec  CRD_REC_BUF,  *pj;
    struct  i1bRec   OUT_BUF,        *po;
    
    pj = &CRD_REC_BUF;
    po = &OUT_BUF;
    Then the similar point in the code as before is
    Code:
    memcpy 9po->Custnum, pj->CrCustnum, 6);
    <snip>
    /* convert packed data field  */
    inPtr = (char *) pj->CrFxfwddelex;
    outPtr = (char *) po->Fxfwddelex;
    for (i = 0; i < 7;  ++1)
    {
      strcpy (outPtr, byte2hex (*inPtr++, hexbuf));
      outPtr  += 2;
    }
    At first I thought the different levels of indirection seemed clear, in that there is a pointer and a character array (inPtr and hexbuf), but then thought further that the compiler should be looking at the output from the function byte2hex (which is a pointer) so it should be ok? Obviously, I am confused! :?

    Actual messages from compiler as follows:
    warning C4047: 'argument' : different levels of indirection
    warning C4024: 'strcpy' : different types : parameter 2

    Any help gratefully received.

  2. #2
    and the hat of wrongness Salem's Avatar
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    char *byte2hex (data, buf)
    unsigned char data;
    char *buf;
    Woah, K&R C old-style declaration. Just how old is this code?

    My initial thought is that either strcpy() or byte2hex is missing a prototype at the point you make the call.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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  3. #3
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    Ancient!

    Yep, it was missing a prototype after all that. Thanks.

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