Invalid non-literal msgid error

Explanation of the problem

This page explains how to fix compilation errors given when wxWidgets translations macros such as _(), wxPLURAL(), wxGETTEXT_IN_CONTEXT or wxGETTEXT_IN_CONTEXT_PLURAL() are used incorrectly. If you’re only interested in the fastest possible workaround, jump to the end but be warned that this is not the best solution!

To understand the problem, you need to know that, due to the way xgettext works, the arguments of these macros should always be literal strings, i.e. either "a usual string" or L"a wide string" but nothing else and since wxWidgets 3.3.0 using them with anything else results in a compilation error.

In the previous versions of wxWidgets, the code compiled but silently didn’t work correctly. New versions improve the situation by catching the problem earlier.

Correct fix

To fix the problem, you need to change the code to use literal strings, e.g. if you have

wxMessageBox(_(wxString::Format("Hello %s", who)));

in your code you need to change it to

wxMessageBox(wxString::Format(_("Hello %s"), who));

so that _() is passed a literal string.

Sometimes fixing the problem is as simple as removing an extraneous occurrence of _(), e.g. if you have

wxPLURAL(_("%d file"), _("%d files"), n)

you should just remove the _() around the arguments as it’s not only not needed but actively prevents this code from working correctly:

wxPLURAL("%d file", "%d files", n)

Workaround

If you really can’t, or don’t want to change the existing code, it can be made to compile in the same way as before by predefining wxNO_REQUIRE_LITERAL_MSGIDS preprocessor symbol, typically at the build system level, i.e. in your makefile, project file etc.

Please note that this is not recommended, as the code still won’t work correctly – but it will at least continue to compile as before.