Thread: Please explain me about Options.c

Option.c ?? please explain me this one. I need only the while portion of it.
/* Utility function to extract option flags from the command line. */

Code:

//Option.c
#include "Everything.h"
#include <stdarg.h>

DWORD Options (int argc, LPCTSTR argv [], LPCTSTR OptStr, ...)

/* argv is the command line.
    The options, if any, start with a '-' in argv[1], argv[2], ...
    OptStr is a text string containing all possible options,
    in one-to-one correspondence with the addresses of Boolean variables
    in the variable argument list (...).
    These flags are set if and only if the corresponding option
    character occurs in argv [1], argv [2], ...
    The return value is the argv index of the first argument beyond the options. */

{
    va_list pFlagList;
    LPBOOL pFlag;
    int iFlag = 0, iArg;

    va_start (pFlagList, OptStr);

    while ((pFlag = va_arg (pFlagList, LPBOOL)) != NULL
                && iFlag < (int)_tcslen (OptStr)) {
        *pFlag = FALSE;
        for (iArg = 1; !(*pFlag) && iArg < argc && argv [iArg] [0] == _T('-'); iArg++)
            *pFlag = _memtchr (argv [iArg], OptStr [iFlag],
                    _tcslen (argv [iArg])) != NULL;
        iFlag++;
    }

    va_end (pFlagList);

    for (iArg = 1; iArg < argc && argv [iArg] [0] == _T('-'); iArg++);

    return iArg;
}

cat.c // I understood this one. Just to show how Options.c is implemented

Code:

/* cat [options] [files]
    Only the -s option is used. Others are ignored.
    -s suppresses error report when a file does not exist */

#include "Everything.h"

#define BUF_SIZE 0x200

static VOID CatFile (HANDLE, HANDLE);
int _tmain (int argc, LPTSTR argv [])
{
    HANDLE hInFile, hStdIn = GetStdHandle (STD_INPUT_HANDLE);
    HANDLE hStdOut = GetStdHandle (STD_OUTPUT_HANDLE);
    BOOL dashS;
    int iArg, iFirstFile;

    /*    dashS will be set only if "-s" is on the command line. */
    /*    iFirstFile is the argv [] index of the first input file. */
    iFirstFile = Options (argc, argv, _T("s"), &dashS, NULL);

    if (iFirstFile == argc) { /* No files in arg list. */
        CatFile (hStdIn, hStdOut);
        return 0;
    } 
    
    /* Process the input files. */
    for (iArg = iFirstFile; iArg < argc; iArg++) {
        hInFile = CreateFile (argv [iArg], GENERIC_READ,
                0, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
        if (hInFile == INVALID_HANDLE_VALUE) {
            if (!dashS) ReportError (_T ("Cat Error: File does not exist."), 0, TRUE);
        } else {
            CatFile (hInFile, hStdOut);
            if (GetLastError() != 0 && !dashS) {
                ReportError (_T ("Cat Error: Could not process file completely."), 0, TRUE);
            }
            CloseHandle (hInFile);
        }
    }
    return 0;
}

static VOID CatFile (HANDLE hInFile, HANDLE hOutFile)
{
    DWORD nIn, nOut;
    BYTE buffer [BUF_SIZE];

    while (ReadFile (hInFile, buffer, BUF_SIZE, &nIn, NULL) && (nIn != 0)
            && WriteFile (hOutFile, buffer, nIn, &nOut, NULL));

    return;
}

Code:

(pFlag = va_arg (pFlagList, LPBOOL)) != NULL

// this is used to check whether we have reached end of the list or not.

Code:

iFlag < (int)_tcslen (OptStr)

// I didn't get it. Why this is used.

Code:

*pFlag = FALSE;    // I did get it too.

Code:

    for (iArg = 1; !(*pFlag) && iArg < argc && argv [iArg] [0] == _T('-'); iArg++)

It will run till iArg = 1 to argc && if (first char of argv is '-')

Code:

            *pFlag = _memtchr (argv [iArg], OptStr [iFlag],
                    _tcslen (argv [iArg])) != NULL;

*pFlag will be set to true in while loop when it encounters '-' on its first run i.e till iFlag is zero, after it I don't understand.


In summary I didn't get why iFlag is used and why it is needed to set pFlag to false .