February 2019 | The Old New Thing

How should I report errors from my Windows Runtime API?

Raymond ChenFebruary 28, 2019Feb 28, 201902/28/19

A customer was implementing a custom Windows Runtime component and wanted to know what the best practices are for reporting errors. Well, it depends on what kind of error it is. One class of errors are unrecoverable errors. For example, if there is an error that represents an internal logic error or other bug in the program, then there is no

The std::map subscript operator is a convenience, but a potentially dangerous one

Raymond ChenFebruary 27, 2019Feb 27, 201902/27/19

The std::map<K, V> class is an associative container of key/value pairs. It also provides a handy subscript operator [] that lets you access the map as if it were an array. That operator is a convenience, but a potentially dangerous one. The problem is that the [] operator is trying to serve two masters. You might use it to read a valu

How to draw a nifty text box in your email message

Raymond ChenFebruary 26, 2019Feb 26, 201902/26/19

In order to help set off content in email messages, for example, to demarcate a code snippet, I will often put it in a box. ... but consider the following class: class Muffin{public: void Bake();}; One of my colleagues apparently was fascinated by this technique and couldn't figure out how it was done. "Okay, I give up. How do y

That time the CEO of a company complained to Congress about Windows file extensions

Raymond ChenFebruary 25, 2019Feb 25, 201902/25/19

Back in the days when it was even more fashionable to hate Microsoft than it is today (but then again, some things never go out of style), I remember that the CEO of a technology company testified in front of Congress to complain about Windows file extensions. The CEO was complaining about anti-competitive practices, and gave as an example th

The 2019/2020 Seattle Symphony subscription season at a glance

Raymond ChenFebruary 22, 2019Feb 22, 201902/22/19

For many years, I've put together a little pocket guide to the Seattle Symphony subscription season for my symphony friends to help them decide which ticket package they want. At some point, we may start subscribing again, but for now, we pick-and-choose individual concerts. Here's the at-a-glance season guide for the 2019/2020 s

How do I permit a minus sign to be entered into my edit control, but only if it’s the first character?

Raymond ChenFebruary 22, 2019Feb 22, 201902/22/19

Last time, we saw how to implement the equivalent of the ES_NUMBER edit control style, but also allow a minus sign. For bonus points, let's allow the minus sign only if it is going at the start of the edit control. We make a tweak to our previous filter to allow minus signs through, but only if the character is being inserted at the start of

How do I allow negative numbers with the <CODE data-lazy-src=

ES_NUMBER edit control style?"/>

How do I allow negative numbers with the `ES_NUMBER` edit control style?

Raymond ChenFebruary 21, 2019Feb 21, 201902/21/19

The ES_NUMBER edit control style limits typed input to digits, but what if you also want to accept negative numbers? How can we extend¹ ES_NUMBER to accept the minus sign? The ES_NUMBER edit control style works by altering the behavior of the edit control when it receives a WM_CHAR. You can do that too! Subclass the edit control and han

The early history of the <CODE data-lazy-src=

ES_NUMBER edit control style"/>

The early history of the `ES_NUMBER` edit control style

Raymond ChenFebruary 20, 2019Feb 20, 201902/20/19

The ES_NUMBER edit control style was added in Windows 95. If the style is set, then the edit control limits typed input to digits. It doesn't do very much, but what it does is kind of handy. As noted in the documentation, this doesn't prevent the user from putting non-digits into the edit control by other means, like pasting with Ctrl+V. It t

How do I convert all these strange Unicode digits into the ones I remember from Sesame Street?

Raymond ChenFebruary 19, 2019Feb 19, 201902/19/19

Suppose you have a Unicode string and you want to do something mathematical with it. You know how to parse DIGIT ZERO "0" through DIGIT NINE "9" but the string may contain Unicode digits like ARABIC-INDIC DIGIT SIX "٦" or DEVANAGARI DIGIT SEVEN "७", and you want to support those too. Help here comes from the FoldString functi

How can I check in Win32 whether a Unicode character is any kind of digit?

Raymond ChenFebruary 18, 2019Feb 18, 201902/18/19

Suppose you have a Unicode code unit wchar_t and you want to know whether it represents a numeric digit. If you have the ICU library, you can check if its code point's u_charType is U_DECIMAL_DIGIT_NUMBER. But what about plain Win32? For Win32, you can use the GetStringTypeW function to obtain properties for each code unit. We ask

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