CODEWITHSUNDEEP
c++winapi
Victor
Victor

Reputation: 14573

-Error reading characters of string

I have the following block of code:

for( CarsPool::CarRecord &record : recs->GetRecords())
{
  LVITEM item;
  item.mask = LVIF_TEXT;
  item.cchTextMax = 6;

  item.iSubItem = 0;
  item.pszText = (LPSTR)(record.getCarName().c_str()); //breakpoint on this line.
  item.iItem = 0;
  ListView_InsertItem(CarsListView, &item);

  item.iSubItem = 1; 
  item.pszText = TEXT("Available");
  ListView_SetItem(CarsListView, &item);

  item.iSubItem = 2;
  item.pszText = (LPSTR)CarsPool::EncodeCarType(record.getCarType());
  ListView_SetItem(CarsListView, &item);
}

The information from Visual Studio Debugger is here:

enter image description here

Why isn't the program able to read the characters from string?

A test has shown me that it works in this way:

MessageBox(hWnd, (LPSTR)(record.getCarName().c_str()), "Test", MB_OK);

Upvotes: 9

Views: 52516

Answers (2)

IInspectable
IInspectable

Reputation: 51345

getCarName likely returns a temporary. After the assignment the temporary object is destroyed and the pointer item.pszText points to invalid memory. You must ensure that the string object is valid during the call to ListView_InsertItem.

std::string text(record.getCarName());
item.iSubItem = 0;
item.pszText = const_cast<LPSTR>(text.c_str());
item.iItem = 0;
ListView_InsertItem(CarsListView, &item);

The const_cast is an artifact of the fact that the Windows API uses the same structure to set and retrieve information. When invoking ListView_InsertItem the structure is immutable, however there is no way to reflect that in the language.

Upvotes: 5

paulsm4
paulsm4

Reputation: 121599

It looks like you're trying to use the value of a C++ "string" in a C/Win32 call.

stdstring.c_str() is the correct way to do it.

... BUT ...

You should strcpy() the string to a temp variable, then make the Win32 call with the temp variable.

Upvotes: 3

Related Questions