warning C4830 "non-portable use of class 'ATL::CStringT<wchar_t, StrTraitMFC_DLL<wchar_t, ATL::ChTraitsCRT<wchar_t>>>' as an argument to a variadic function

Question

We were migrating our codebase from VS2015 to VS2022, we have some c++ components and updated them also to c++20 and then we encounter hundreds of warnings about C4830 "non-portable use of class 'ATL::CStringT<wchar_t, StrTraitMFC_DLL<wchar_t, ATL::ChTraitsCRT<wchar_t>>>' as an argument to a variadic function. We use a lot of CString in variadic functions such as String Format and for our own loggings and printings.

What is the best way to deal with this error

Answer 1

Hi, @Rodriguez, Daniel C [AUTOSOL/RS/MNL]

Have you read document: C4840. This warning is available beginning in Visual Studio 2017. The document also prodives samples and way to fix it:

For strings built and managed using CStringW, the provided operator LPCWSTR() should be used to cast a CStringW object to the C-style string pointer expected by the format string:

 CStringW str1;  
 CStringW str2;  
  // ...  
 str1.Format("%s", static_cast<LPCWSTR>(str2));  

Best regards,

Minxin Yu

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