Wide String Shims for std::exception

The latest release of STLSoft (1.9.102) includes wide string additions to the string access shims for std::exception (and derived types). The most obvious and immediate benefit is that code using FastFormat and/or Pantheios in wide string builds can now work seamlessly with exceptions, just as has always been the case in multibyte string builds:

#include <fastformat/ff.hpp>

. . .

#include <pantheios/pan.hpp>

. . . 

int main()

{

. . .

  catch(std::exception& x)

  {

    pan::log_CRITICAL(L"exception: ", x);

    ff::fmtln(std::wcerr, L"program: {0}", x);

  }

. . . 

WinSTL Registry library mods and fixes, part 3: exception-safety

In reviewing the implementation of the WinSTL Registry Library's winstl::basic_reg_value class - as described in part 1 and part 2 of this series of posts - I've also spotted a defect in exception-safety.

Consider the (chopped-down) definition of the basic_reg_value class:

template < . . . >
class basic_reg_value
{
. . .
private:
hkey_type    m_hkey; // The parent key of the value
string_type  m_name; // The name of the value
. . . // other members
};

The m_hkey member is obtained via winstl::reg_traits<>::reg_dup_key(). It is the basic_reg_value class itself that provides the RAII. Consequently, if any exception occur during its constructor, the release of m_hkey will not be carried out.

Since the m_name is a string class instance, its constructor can throw. Consequently, basic_reg_value is not exception safe.

Thankfully, the fix is very simple. Simply reverse the order of declaration of the two members. If m_name's constructor throws, that'll happen before the key duplication takes place. If the key duplication throws an exception, the (fully constructed) m_name's destructor will be invoked. Q.E.D.

STLSoft 1.9.51 released

This latest release contains only two changes, but they're interesting nonetheless.

The first is a workaround for a defect in VC6. This was found in stlsoft::conversion_error, and comes about as follows. stlsoft::conversion_error is defined along the lines of:


class conversion_error_base

  : public std::runtime_error

{

  . . .

public: // Construction

  virtual ~conversion_error_base() = 0;

  . . .

};



class conversion_error

  : public conversion_error_base

{

  . . .

};



The highlighted line is the problem for VC++ 6. The code it generates is defective such that when an instance of any derived class is thrown, the exception does not get thrown, merely hangs about in the current scope, and the program execution carries on as if no exception was thrown.

The second change is a correction for a defect in the string access shim functions for the SYSTEMTIME type, whereby conversion of an invalid time resulted in a fault, because the calculation for the total length of the resultant string did not take account the fact that the Windows Time API functions returns 0 if the time instance is invalid. The consequence of fixing this defect has resulted in some nice refactoring, so there's some silver lining.

Coming soon: releases of VOLE, flecxx, Pantheios, and FastFormat.