3112. system_error and filesystem_error constructors taking a string may not be able to meet their postconditions

Section: 19.5.8.2 [syserr.syserr.members], 31.12.7.2 [fs.filesystem.error.members] Status: C++20 Submitter: Tim Song Opened: 2018-05-10 Last modified: 2021-06-06

Priority: 0

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Discussion:

The constructors of system_error and filesystem_error taking a std::string what_arg are specified to have a postcondition of string(what()).find(what_arg) != string::npos (or the equivalent with string_view). This is not possible if what_arg contains an embedded null character.

[2019-01-20 Reflector prioritization]

Set Priority to 0 and status to Tentatively Ready

Proposed resolution:

This wording is relative to N4727.

Drafting note: This contains a drive-by editorial change to use string_view for these postconditions rather than string.

1. Edit 19.5.8.2 [syserr.syserr.members] p1-4 as indicated:

   system_error(error_code ec, const string& what_arg);
   

   -1- Effects: Constructs an object of class system_error.

   -2- Postconditions: code() == ec and string_view(what()).find(what_arg.c_str()) != string_view::npos.

   system_error(error_code ec, const char* what_arg);
   

   -3- Effects: Constructs an object of class system_error.

   -4- Postconditions: code() == ec and string_view(what()).find(what_arg) != string_view::npos.

2. Edit 19.5.8.2 [syserr.syserr.members] p7-10 as indicated:

   system_error(int ev, const error_category& ecat, const std::string& what_arg);
   

   -7- Effects: Constructs an object of class system_error.

   -8- Postconditions: code() == error_code(ev, ecat) and string_view(what()).find(what_arg.c_str()) != string_view::npos.

   system_error(int ev, const error_category& ecat, const char* what_arg);
   

   -9- Effects: Constructs an object of class system_error.

   -10- Postconditions: code() == error_code(ev, ecat) and string_view(what()).find(what_arg) != string_view::npos.

3. Edit [fs.filesystem_error.members] p2-4 as indicated:

   filesystem_error(const string& what_arg, error_code ec);
   

   -2- Postconditions:

   • code() == ec,
   • path1().empty() == true,
   • path2().empty() == true, and
   • string_view(what()).find(what_arg.c_str()) != string_view::npos.

   filesystem_error(const string& what_arg, const path& p1, error_code ec);
   

   -3- Postconditions:

   • code() == ec,
   • path1() returns a reference to the stored copy of p1,
   • path2().empty() == true, and
   • string_view(what()).find(what_arg.c_str()) != string_view::npos.

   filesystem_error(const string& what_arg, const path& p1, const path& p2, error_code ec);
   

   -4- Postconditions:

   • code() == ec,
   • path1() returns a reference to the stored copy of p1,
   • path2() returns a reference to the stored copy of p2,
   • string_view(what()).find(what_arg.c_str()) != string_view::npos.