Unable to Read from File while using ReadFIle() function in C++ - c++

Question

I am facing some issues while reading data from file using ReadFile() function of C++ (Microsoft specific probably).
Here is my code
Write On File
void ClientA::SharePublicKey()
{
printf("Sharing Public Key\n");
HANDLE hFile = NULL;
hFile = CreateFile(TEXT("D:\\My_Proj\\shared\\PublicKeyB.txt"), // name of the write
GENERIC_WRITE, // open for writing
FILE_SHARE_WRITE, // do not share
NULL, // default security
CREATE_NEW, // create new file only
FILE_ATTRIBUTE_NORMAL, // normal file
NULL); // no attr. template
if (hFile == INVALID_HANDLE_VALUE)
{
//DisplayError(TEXT("CreateFile"));
//_tprintf(TEXT("Terminal failure: Unable to open file \"%s\" for write.\n"), argv[1]);
return;
}
// _tprintf(TEXT("Writing %d bytes to %s.\n"), dwBytesToWrite, argv[1]);
bool bErrorFlag = WriteFile(
hFile, // open file handle
pbPublicKey, // start of data to write
dwPublicKeyLen, // number of bytes to write
&lpNumberOfBytesWritten, // number of bytes that were written
NULL); // no overlapped structure
if (FALSE == bErrorFlag)
{
// DisplayError(TEXT("WriteFile"));
printf("Terminal failure: Unable to write to file.\n");
return;
}
else
{
if (lpNumberOfBytesWritten != dwPublicKeyLen)
{
// This is an error because a synchronous write that results in
// success (WriteFile returns TRUE) should write all data as
// requested. This would not necessarily be the case for
// asynchronous writes.
printf("Error: dwBytesWritten != dwBytesToWrite\n");
}
else
{
// _tprintf(TEXT("Wrote %d bytes to %s successfully.\n"), dwBytesWritten, argv[1]);
}
}
CloseHandle(hFile);
}
Read That File
void ClientA::ReadPublicKeyOfOtherPeer()
{
HANDLE hFile = NULL;
DWORD dwBytesRead = 0;
BYTE* ReadBuffer = NULL;
OVERLAPPED ol = {0};
hFile = CreateFile(TEXT("D:\\My_Proj\\shared\\PublicKeyB.txt"), // file to open
GENERIC_READ, // open for reading
FILE_SHARE_READ, // share for reading
NULL, // default security
OPEN_EXISTING, // existing file only
FILE_ATTRIBUTE_NORMAL | FILE_FLAG_OVERLAPPED, // normal file
NULL // no attr. template
);
if (hFile == INVALID_HANDLE_VALUE)
{
_tprintf(TEXT("CreateFile\n"));
_tprintf(TEXT("Terminal failure: unable to open file \"%s\" for read.\n"));
printf("Error %x\n", GetLastError());
return;
}
if( FALSE == ReadFile(hFile, ReadBuffer, dwPublicKeyLen, &lpNumberOfBytesWritten, &ol) )
{
// DisplayError(TEXT("ReadFile"));
printf("Terminal failure: Unable to read from file.\n GetLastError=%08x\n", GetLastError());
CloseHandle(hFile);
return;
}
if (dwBytesRead > 0 && dwBytesRead <= dwPublicKeyLen-1)
{
ReadBuffer[dwBytesRead]='\0'; // NULL character
//_tprintf(TEXT("Data read from %s (%d bytes): \n"), argv[1], dwBytesRead);
printf("%s\n", ReadBuffer);
}
else if (dwBytesRead == 0)
{
//_tprintf(TEXT("No data read from file %s\n"), argv[1]);
}
else
{
// printf("\n ** Unexpected value for dwBytesRead ** \n");
}
retrievedPublicByteArray = ReadBuffer;
CloseHandle(hFile);
}
By SharePublicKey method I am saving the data in a file. And I have checked that it successfully saves data on the file and the data on the files are seems to be valid.
And by ReadPublicKeyOfOtherPeer method I am reading the file which was previously saved. But reading is not successful In out put I found the following line -
Terminal failure: Unable to read from file.
GetLastError=000003e6

Answer 1

You are passing uninitialized pointer ReadBuffer to ReadFile. You need a buffer that is large enough to receive the results.