How to get the width of a string in pixels(/logical units)?

Question

I am following a tutorial here, to add a horizontal scrollbar to a list control. Everything there works except the TextWidth() function (VC++ 2012 says it's undefined) so I found this question. But I have no idea how to initialize a hdc, so I tried this. But GetTextExtentPoint32 keeps returning zero.

Any idea how I can solve this?

My code looks like this (after edit):

SIZE Size;
HDC hdc=GetDC(hWnd);
iResult=GetTextExtentPoint32(hdc, szMessage, MESSAGE_SIZE, &Size);

(szMessage contains user input)

Answer 1

My way:

SIZE sz;
HFONT font = GetFont();     //GetFont() is part of WTL. If using raw WinAPI it needs to get font in other means.
HDC hdc = GetDC(NULL);
SelectObject(hdc, font);    //attach font to hdc

GetTextExtentPoint32(hdc, text, lstrlenW(text), &sz);
ReleaseDC(NULL, hdc);

Answer 2

Ok so to answer my question: The code above (see question) gives a way too high value for Size.cx because MESSAGE_SIZE is 1000 and not the size of the actual string so I used strMessage.c_str and strMessage.size() instead. This still gave some small inaccuracies with the output, I assumed this was because the wrong font was used, so I manually made a font. Now it gives a correct value for Size.cx. The code now looks like this:

int iHorExt=0;
SIZE Size;
int iCurHorExt=0 // iCurHorExt is actually a global var to prevent it from being reset to 0 evertime the code executes
string strMessage="Random user input here!"

HDC hdc=GetDC(hDlg);

//Random font
HFONT hFont=CreateFont(15, 5, NULL, NULL, FW_MEDIUM, false, false, false, DEFAULT_CHARSET, OUT_DEFAULT_PRECIS, CLIP_DEFAULT_PRECIS, ANTIALIASED_QUALITY, FF_ROMAN, "Times New Roman");

//change font of the control
SendDlgItemMessage(hDlg, IDC_LIST1, WM_SETFONT, (WPARAM)hFont, true);


SelectObject(hdc, hFont);

int iResult=GetTextExtentPoint32(hdc, strMessage.c_str(), strMessage.size(), &Size);
if(iResult!=0)
{
    iHorExt=Size.cx;
    if(iHorExt>iCurHorExt)
    {
        iCurHorExt=iHorExt;
    }
}

later in the code:

SendDlgItemMessage(hDlg, IDC_LIST1, LB_SETHORIZONTALEXTENT, iCurHorExt, NULL);

Edit:

SelectObject(hdc, (HFONT)SendDlgItemMessage(hDlg, IDC_LIST1, WM_GETFONT, NULL, NULL));

Works too and doesn't require you to make a font or edit the font of the control