stdarg, checking for # of entered arguments

Code:

---

void CMatrix::SetRow(unsigned short iRowNum, ...)
{
        if (m_pdMatrixData == NULL) return;
        // Error Checking;

        va_list vaList;
        // Variable length argument lists... defined in stdarg.h;

        va_start(vaList, iRowNum);

        for (int i = 0; i < m_iDimension[0]; i++)
        {

                m_pdMatrixData[iRowNum][i] = va_arg(vaList, double);
        }
}

---

How would I go about checking that the number of arguments entered is less than m_iDimension[0]? I searched on MSDN, and I tried something like sizeof(vaList)/sizeof(double) < m_iDimension[0] but that didn't seem to work.
Any help would be much appreciated.

> How would I go about checking that the number of arguments entered is less than m_iDimension[0]?
You can't - at least not in any portable way

Consider these two stdarg type functions
1. printf
The number of arguments expected (not enforced) is determined by the number of % conversions in the control string. What happens when you pass more/less than the expected number is implementation defined (but its rarely good)

2. execl
The of program arguments is terminated by a NULL pointer.

In both cases, the called function knows how to work out the number of expected parameters, even if the programmer got it wrong.