Read CByteArray from CFile

Question

I'm writring CByteArray to file:

    CFile myFile;
CByteArray m_baToques;

    if(myFile.Open(_T(file), CFile::modeReadWrite | CFile::modeCreate))
    {
        myFile.Write(m_baToques.GetData(),m_baToques.GetSize());
        myFile.Write(m_baDst.GetData(), m_baDst.GetSize());
        myFile.Write(m_baFeriados.GetData(), m_baFeriados.GetSize());
    }

Now How to read CByteArray from file?

I try:

    CFile myFile;    
    if(myFile.Open(_T(file), CFile::modeReadWrite | CFile::modeCreate))
    {
        myFile.Read(m_baToques,m_baToques.GetSize());
        myFile.Read(m_baDst, m_baDst.GetSize());
        myFile.Read(m_baFeriados, m_baFeriados.GetSize());
    }

error C2664: 'CFile::Read' : cannot convert parameter 1 from 'CByteArray' to 'void *'

If your code does not work, you should add *why*. What does it do, what does it not do? Does it compile? Does it run? — Jongware, Nov 30 '13 at 10:03

score 2 · Answer 1 · edited Feb 01 '21 at 22:36

to complete question with full functional code: (tested under Visual studio 2017)

BOOL ReadBinaryFile(TCHAR * filename) {

    CFileStatus filestatus;
    BOOL ok = CFile::GetStatus(filename, filestatus);
    if (!ok)
        return FALSE;

    CFile myFile;
    ok = myFile.Open(filename, CFile::modeRead | CFile::typeBinary | CFile::modeNoTruncate);
    if (!ok)
        return FALSE;

    INT_PTR SIZE = (INT_PTR) filestatus.m_size;

    // To read into a CByteArray, we need to allocate a buffer via CByteArray and get a pointer to said buffer that we can use for lpBuf:
    CByteArray buffer;
    buffer.SetSize(SIZE); // ensure that buffer is allocated and the size we want it
    UINT bytesRead = myFile.Read(buffer.GetData(), SIZE);

    myFile.Close();
    return TRUE;
}

score 1 · Accepted Answer · edited Jun 20 '20 at 09:12

Looking at the documentation for CFile::Read, we see that it takes two parameters:

virtual UINT CFile::Read(void* lpBuf, UINT nCount);

lpBuf

Pointer to the user-supplied buffer that is to receive the data read from the file.

nCount

The maximum number of bytes to be read from the file. For text-mode files, carriage return–linefeed pairs are counted as single characters.

lpBuf is not of type CByteArray. It is void*. Thus the compiler error.

To read into a CByteArray, we need to allocate a buffer via CByteArray and get a pointer to said buffer that we can use for lpBuf:

CByteArray buffer;
buffer.SetSize(1024); // ensure that buffer is allocated and the size we want it
UINT bytesRead = myFile.Read(buffer.GetData(), buffer.GetSize());
// use bytesRead value and data now in buffer as needed

Note, that in your question, you have the following line on the read path:

if(myFile.Open(_T(file), CFile::modeReadWrite | CFile::modeCreate))

The CFile::modeCreate will cause the file to be truncated to 0 bytes. There won't be anything to read.

Did you mean to write something more like this?

if(myFile.Open(_T(file), CFile::modeRead | CFile::typeBinary | CFile::modeNoTruncate))

Read CByteArray from CFile

2 Answers2