How do I save the result from GetProfileBinary into a smart pointer? - visual-c++

Question

At the moment I have the following member variable in a class:
BYTE *m_pbyImportColumnMappings;
In one of the classes we attempt to read existing data from the registry, and if it is not present, we allocate it. So far, I have changed it like this:
void CImportOCLMAssignmentHistoryDlg::ReadSettings()
{
UINT uSize;
m_dwImportFlags = theApp.GetNumberSetting(theApp.GetActiveScheduleSection(_T("Options")),
_T("ImportFlags"), ImportAssignment::None);
theApp.GetProfileBinary(theApp.GetActiveScheduleSection(_T("Options")),
_T("ImportColumnMappings"), (LPBYTE*)&m_pbyImportColumnMappings, &uSize);
// Reset memory buffer (if required)
if (uSize != (sizeof(BYTE) * 15))
{
if (uSize > 0)
{
delete[] m_pbyImportColumnMappings;
m_pbyImportColumnMappings = nullptr;
}
m_pbyImportColumnMappings = new BYTE[15];
// Default values
const gsl::span column_mappings(m_pbyImportColumnMappings, 15);
std::fill(begin(column_mappings), end(column_mappings), -1);
/*
m_pbyImportColumnMappings[0] = -1;
m_pbyImportColumnMappings[1] = -1;
m_pbyImportColumnMappings[2] = -1;
m_pbyImportColumnMappings[3] = -1;
m_pbyImportColumnMappings[4] = -1;
m_pbyImportColumnMappings[5] = -1;
m_pbyImportColumnMappings[6] = -1;
m_pbyImportColumnMappings[7] = -1;
m_pbyImportColumnMappings[8] = -1;
m_pbyImportColumnMappings[9] = -1;
m_pbyImportColumnMappings[10] = -1;
m_pbyImportColumnMappings[11] = -1;
m_pbyImportColumnMappings[12] = -1;
m_pbyImportColumnMappings[13] = -1;
m_pbyImportColumnMappings[14] = -1;
*/
}
}
My initial change was to use a gsl::span to suppress several warnings about using pointer arithemetic. But I don't know how to turn m_pbyImportColumnMappings into a smart pointer, given the fact that we are attempting to initially populate it from GetProfileBinary.
If I could turn it into a smart pointer then I would not need to deallocate the memory when the class goes out of scope.
In a related answer this code was suggested:
theApp.GetProfileBinary(strSection, strEntry,
reinterpret_cast<LPBYTE*>(&pALI), &uBytesRead);
std::unique_ptr<BYTE[]> cleanup(reinterpret_cast<BYTE*>(pALI));
But, I am not sure how to apply that cleanup method given teh fact we are dealing with a member variable of the class as opposed to an isolated variable in a function.

Answer 1

For a cleaner code, consider using std::vector and a temporary buffer
std::vector<BYTE> m_mapping;
m_mapping.resize(15, -1);
...
UINT len = 0;
BYTE* temp = nullptr;
AfxGetApp()->GetProfileBinary(_T("setting"), _T("key"), &temp, &len);
std::unique_ptr<BYTE[]> cleanup(temp);
if (len == m_mapping.size() * sizeof(m_mapping[0]))
memcpy(m_mapping.data(), temp, len);
else
std::fill(m_mapping.begin(), m_mapping.end(), -1);
std::vector also has automatic cleanup and additional methods.
Otherwise, using std::unique_ptr to replace new/delete for this member data, can be a bit of a nightmare. Example:
m_mapping = nullptr;
GetProfileBinary("setting", "key", &m_mapping, &uSize);
if (uSize != (sizeof(BYTE) * 15))
{
{ std::unique_ptr<BYTE[]> cleanup(m_mapping); }
//delete memory immediately after exiting scope
//note the extra brackets
//allocate new memory and don't manage it anymore
m_mapping = std::make_unique<BYTE[]>(15).release();
if(m_mapping)
for (int i = 0; i < 15; i++) m_mapping[i] = -1;
}
Here we are not able to take advantage of std::unique_ptr memory management, it's only used to turn off warnings.
You don't need any casting here because it just happens that m_pbyImportColumnMappings is BYTE, and GetProfileBinary expects BYTE, it allocates memory using new BYTE