This page is a snapshot from the LWG issues list, see the Library Active Issues List for more information and the meaning of New status.

4512. The system_encoded_string() and generic_system_encoded_string() member functions of std::filesystem::path are misnamed

Section: 31.12.6.1 [fs.class.path.general], 31.12.6.3.2 [fs.path.type.cvt], 31.12.6.5.6 [fs.path.native.obs], 31.12.6.5.7 [fs.path.generic.obs], D.22.2 [depr.fs.path.obs] Status: New Submitter: Tom Honermann Opened: 2026-01-11 Last modified: 2026-01-18

Priority: Not Prioritized

View all issues with New status.

Discussion:

Addresses US 189-304

The system_encoded_string() and generic_system_encoded_string() member functions of std::filesystem::path are misnamed. These functions were added as renamed versions of string() and generic_string() respectively by P2319R5 ("Prevent path presentation problems"). The original function names are now deprecated.

The C++ standard does not define "system encoding" and casual use of such a term is at best ambiguous. In common language, one might expect the "system encoding" to correspond to the environment encoding (for which std::text_encoding::environment() provides a definition) or the encoding of the current locale. However, neither of these encodings corresponds to the encoding these functions are expected to use. 31.12.6.3.2 [fs.path.type.cvt] defines "native encoding" and, for char-based filesystem paths, states (in a note) that "For Windows-based operating systems, the native ordinary encoding is determined by calling a Windows API function." It is not specified which Windows API function is consulted, but existing implementations call AreFileApisANSI() to choose between the Active Code Page (CP_ACP) and the OEM Code Page (CP_OEMCP). Microsoft's implementation also checks for a thread-local locale and, if the locale encoding is UTF-8, prefers that (CP_UTF8) over either of the other two.

Proposed resolution:

This wording is relative to N5032.

1. Modify 31.12.6.1 [fs.class.path.general], class path synopsis, as indicated:

   namespace std::filesystem {
     class path {
     public:
       […]
       // 31.12.6.5.6 [fs.path.native.obs], native format observers
       […]
       std::string display_string() const;
       std::string systemnative_encoded_string() const;
       std::wstring wstring() const;
       […]
       
       // 31.12.6.5.7 [fs.path.generic.obs], generic format observers
       […]
       std::string generic_display_string() const;
       std::string generic_systemnative_encoded_string() const;
       std::wstring generic_wstring() const;
       […]
     };
   }
   

2. Modify 31.12.6.3.2 [fs.path.type.cvt] as indicated:

   -2- For member function arguments that take character sequences representing paths and for member functions returning strings, value type and encoding conversion is performed if the value type of the argument or return value differs from path::value_type. For the argument or return value, the method of conversion and the encoding to be converted to is determined by its value type:

   • (2.1) — char: The encoding is the native ordinary encoding. The method of conversion, if any, is operating system dependent.

     [Note 1: For POSIX-based operating systems path::value_type is char so no conversion from char value type arguments or to char value type return values is performed. For Windows-based operating systems, the native ordinary encoding is determined by calling a Windows API functionthe current locale encoding and the Windows AreFileApisANSI function. — end note]

     […]

   • (2.2) — […]

   • […]

3. Modify 31.12.6.5.6 [fs.path.native.obs] as indicated:

   std::string systemnative_encoded_string() const;
   std::wstring wstring() const;
   std::u8string u8string() const;
   std::u16string u16string() const;
   std::u32string u32string() const;
   

   -7- Returns: native().

   -8- Remarks: Conversion, if any, is performed as specified by 31.12.6.3 [fs.path.cvt].

4. Modify 31.12.6.5.7 [fs.path.generic.obs] as indicated:

   std::string generic_systemnative_encoded_string() const;
   std::wstring generic_wstring() const;
   std::u8string generic_u8string() const;
   std::u16string generic_u16string() const;
   std::u32string generic_u32string() const;
   

   -5- Returns: The pathname in the generic format.

   -6- Remarks: Conversion, if any, is specified by 31.12.6.3 [fs.path.cvt].

5. Modify D.22.2 [depr.fs.path.obs] as indicated:

   std::string string() const;
   

   -2- Returns: systemnative_encoded_string().

   std::string generic_string() const;
   

   -3- Returns: generic_systemnative_encoded_string().