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Asked: 2026-05-29T07:24:17+00:00

I am reading Programming.Windows.5th.Edition,Charles Petzold when I was doing the Figure 4-5. SYSMETS1.C,I met

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I am reading

Programming.Windows.5th.Edition,Charles Petzold

when I was doing the Figure 4-5. SYSMETS1.C,I met the following codes:

cxCaps = (tm.tmPitchAndFamily & 1 ? 3 : 2) * cxChar / 2 ;

and there are explanations in the book,

SYSMETS1 also saves an average width of uppercase letters in the static variable cxCaps. For a fixed-pitch font, cxCaps would equal cxChar. For a variable-width font, cxCaps is set to 150 percent of cxChar. The low bit of the tmPitchAndFamily field in the TEXTMETRIC structure is 1 for a variable-width font and 0 for a fixed-pitch font. SYSMETS1 uses this bit to calculate cxCaps from cxChar.

Now that cxCaps is set to 150 percent of cxChar,I think it should be

cxCaps = (tm.tmPitchAndFamily & 1 ? 3.0 : 2.0) * cxChar / 2 ;

Can you explain it for me?Thanks!

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1 Answer

  1. Editorial Team

    It is trying to calculate an integer result, expressed in pixels. The effective calculation is (3 * cxChar) / 2, not 3 * (cxChar / 2). Presumably the latter one is giving you pause.

    It’s going to get rounded down for a proportional font but will never be off by more than a single pixel. It doesn’t matter since the value is only a guess anyway, the actual width is different for every glyph in a proportional font.

    No points scored for readability, you could perhaps rewrite it like this:

    bool proportional = tm.tmPitchAndFamily & TMPF_FIXED_PITCH;
if (proportional) cxCaps = (3 * cxChar) / 2;
else cxCaps = cxChar;

    Note how the flag has the wrong name, perhaps the reason Petzold wrote it like that.

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