将 std::make_unique 与 GetProfileBinary function 调用一起使用

Question

I have seen this answer ( Advantages of using std::make_unique over new operator ) where it states:

Don't use make_unique if you need a custom deleter or are adopting a raw pointer from elsewhere .

This is is my code:

void CAutomaticBackupSettingsPage::GetLastBackupDate(COleDateTime& rBackupDate)
{
    DATE* pDatTime = nullptr;
    UINT uSize;

    theApp.GetProfileBinary(_T("Options"), _T("BackupLastBackupDate"), pointer_cast<LPBYTE*>(&pDatTime), &uSize);
    if (uSize == sizeof(DATE))
        rBackupDate = *pDatTime;
    else
        rBackupDate = COleDateTime::GetCurrentTime();

    delete[] pDatTime;
    pDatTime = nullptr;
}

Code analysis gives me two warnings:

and

The latter warning suggests I use std::make_unique but since my pointer data is returned from the GetProfileBinary call, and given the statement in the related question, does that mean I should not use std::make_unique ? I admit it is something I have not done before.

---

The useage of GetProfileBinary clearly states:

GetProfileBinary allocates a buffer and returns its address in *ppData . The caller is responsible for freeing the buffer using delete[] .

Answer 1

pDateTime is supposed to be nullptr , and GetProfileBinary handles the allocation. Code Analysis mistakenly thinks you forgot the allocation.

It does need to check for success before calling delete[] . We can't use delete[]pDatTime because pDatTime is not an array. But GetProfileBinary allocates using new BYTE[size] , so we need to cast back to BYTE .

You can also add a NULL check before reading pDatTime , that might make Code Analysis happy.

if (pDatTime && uSize == sizeof(DATE))
    rBackupDate = *pDatTime;
else
    rBackupDate = COleDateTime::GetCurrentTime();
if(pDatTime) delete[](BYTE*)pDatTime;

You can use std::unique_ptr<BYTE[]> cleanup((BYTE*)pDatTime) for deletion, but this has to be after GetProfileBinary is called.

Example:

DATE* pDatTime = nullptr;
GetProfileBinary(_T("Options"), _T("BackupLastBackupDate"), (LPBYTE*)(&pDatTime), &uSize);
std::unique_ptr<BYTE[]> cleanup((BYTE*)pDatTime); //automatic delete

if (pDatTime && uSize == sizeof(DATE))
    rBackupDate = *pDatTime;
else
    rBackupDate = COleDateTime::GetCurrentTime();

//pDatTime = NULL; <- Error when used with unique_ptr
...
//pDatTime is deleted later, when `cleanup` goes out of scope