How should I report errors from my Windows Runtime API?

Raymond Chen February 28, 2019 Feb 28, 2019 02/28/19

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 ...

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

Raymond Chen February 27, 2019 Feb 27, 2019 02/27/19

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 ...

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

Raymond Chen February 22, 2019 Feb 22, 2019 02/22/19

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 ES_NUMBER edit control style?

Raymond Chen February 21, 2019 Feb 21, 2019 02/21/19

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 ...

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

Raymond Chen February 19, 2019 Feb 19, 2019 02/19/19

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 ...

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

Raymond Chen February 18, 2019 Feb 18, 2019 02/18/19

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 ...