msvc_pbd.cc

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/*
    Copyright (C) 2009 John Emmas

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

*/

#ifdef COMPILER_MSVC

#include <WTypes.h>

extern "C" WINBASEAPI BOOL WINAPI
CreateHardLinkA( LPCSTR lpFileName,
                                 LPCSTR lpExistingFileName,
                                 LPSECURITY_ATTRIBUTES lpSecurityAttributes ); // Needs kernel32.lib on anything higher than Win2K

#include <algorithm>
#include <string>
#include <io.h>
#include <math.h>
#include <fcntl.h>
#include <errno.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <pbd/error.h>
#include <ardourext/misc.h>
#include <ardourext/pthread.h> // Should ensure that we include the right
                               // version - but we'll check anyway, later

#include <glibmm.h>

#define DELTA_EPOCH_IN_MICROSECS  11644473600000000Ui64

struct timezone
{
        int  tz_minuteswest; /* minutes W of Greenwich */
        int  tz_dsttime;     /* type of dst correction */
};

LIBPBD_API int PBD_APICALLTYPE
gettimeofday(struct timeval *__restrict tv, __timezone_ptr_t tz) // Does this need to be exported ?
{
FILETIME ft;
unsigned __int64 tmpres = 0;
static int tzflag = 0;

        if (NULL != tv)
        {
                GetSystemTimeAsFileTime(&ft);

                tmpres |= ft.dwHighDateTime;
                tmpres <<= 32;
                tmpres |= ft.dwLowDateTime;

                /*converting file time to unix epoch*/
                tmpres /= 10;  /*convert into microseconds*/
                tmpres -= DELTA_EPOCH_IN_MICROSECS;
                tv->tv_sec = (long)(tmpres / 1000000UL);
                tv->tv_usec = (long)(tmpres % 1000000UL);
        }

        if (NULL != tz)
        {
                struct timezone *ptz = static_cast<struct timezone*> (tz);
                if (!tzflag)
                {
                        _tzset();
                        tzflag++;
                }
                if (ptz)
                {
                        ptz->tz_minuteswest = _timezone / 60;
                        ptz->tz_dsttime = _daylight;
                }
        }

        return 0;
}

// Define the default comparison operators for Windows (ptw32) 'pthread_t' (not used
// by Ardour AFAIK but would be needed if an array of 'pthread_t' had to be sorted).
#ifndef PTHREAD_H   // Defined by PTW32 (Linux and other versions define _PTHREAD_H)
#error "An incompatible version of 'pthread.h' is #included. Use only the Windows (ptw32) version!"
#else
LIBPBD_API bool operator>  (const pthread_t& lhs, const pthread_t& rhs)
{
        return (std::greater<void*>()(lhs.p, rhs.p));
}

LIBPBD_API bool operator<  (const pthread_t& lhs, const pthread_t& rhs)
{
        return (std::less<void*>()(lhs.p, rhs.p));
}

LIBPBD_API bool operator!= (const pthread_t& lhs, const pthread_t& rhs)
{
        return (std::not_equal_to<void*>()(lhs.p, rhs.p));
}

LIBPBD_API bool operator== (const pthread_t& lhs, const pthread_t& rhs)
{
        return (!(lhs != rhs));
}
#endif

// Functions supplied (later) to std::transform
//***************************************************************
//
//      invert_backslash()
//
// Examines a supplied ASCII character and (if the character is
// a backslash) converts it to a forward slash,
//
//      Returns:
//
//    The supplied character (converted, if it was a backslash)
//
char invert_backslash(char character)
{
        if ('\\' == character)
                character = '/';

        return (character);
}

//***************************************************************
//
//      invert_forwardslash()
//
// Examines a supplied ASCII character and (if the character is
// a forward slash) converts it to a backslash,
//
//      Returns:
//
//    The supplied character (converted, if it was a fwd slash)
//
char invert_forwardslash(char character)
{
        if ('/' == character)
                character = '\\';

        return (character);
}


//***************************************************************
//
//      pread()
//
// Emulates pread() using _lseek()/_read()/_lseek().
//
//      Returns:
//
//    On Success: The number of bytes read from the file
//    On Failure: -1
//
LIBPBD_API ssize_t PBD_APICALLTYPE
pread(int handle, void *buf, size_t nbytes, off_t offset)
{
int old_errno;
ssize_t ret;

        off_t old_offset = _tell(handle);

        if (0 > old_offset)
                ret = (-1);
        else
        {
                _lseek(handle, offset, SEEK_SET);
                ret = _read(handle, buf, nbytes);

                old_errno = errno;
                _lseek(handle, old_offset, SEEK_SET);
                errno = old_errno;
        }

        return (ret);
}


//***************************************************************
//
//      pwrite()
//
// Emulates pwrite() using _lseek()/_write()/_lseek().
//
//      Returns:
//
//    On Success: The number of bytes written to the file
//    On Failure: -1
//
LIBPBD_API ssize_t PBD_APICALLTYPE
pwrite(int handle, const void *buf, size_t nbytes, off_t offset)
{
int old_errno;
ssize_t ret;

        off_t old_offset = _lseek(handle, offset, SEEK_SET);

        if (0 > old_offset)
                ret = (-1);
        else
        {
                ret = _write(handle, buf, nbytes);

                old_errno = errno;
                _lseek(handle, old_offset, SEEK_SET);
                errno = old_errno;
        }

        return (ret);
}

//***************************************************************
//
//      round()
//
// Emulates round() using floor().
//
//      Returns:
//
//    On Success: The largest integer that is less than or
//                equal to 'x'.
//    On Failure: None
//
LIBPBD_API double PBD_APICALLTYPE
round(double x)
{
        return (floor(x));
}

//***************************************************************
//
//      trunc()
//
// Emulates trunc() using floor() and ceil().
//
//      Returns:
//
//    On Success: The largest integer whose magnitude is less
//                than or equal to 'x' (regardless of sign).
//    On Failure: None
//
LIBPBD_API double PBD_APICALLTYPE
trunc(double x)
{
        if (x < 0)
                return (ceil(x));

        return (floor(x));
}

//***************************************************************
//
//      log2()
//
// Emulates C99 log2() using log().
//
//      Returns:
//
//    On Success: The binary (base-2) logarithm of 'x'
//                (e.g. log2(1024) == 10).
//    On Failure: None, except that calling log(x) should generate
//                an appropriate error for us (such as ERANGE etc).
//
LIBPBD_API double PBD_APICALLTYPE
log2(double x)
{
        return (log(x) / log((double)2.0));
}

namespace PBD {

//***************************************************************
//
//      TestForMinimumSpecOS()
//
// Tests the user's OS to see if it is Win2K or later (could be
// expanded quite easily to accommodate other OS's)
//
//      Returns:
//
//    On Success: TRUE (if the user's OS matches the minimum spec)
//    On Failure: FALSE otherwise
//
LIBPBD_API bool PBD_APICALLTYPE
TestForMinimumSpecOS(char *revision /* currently ignored */)
{
bool bRet = true;
#ifdef PLATFORM_WINDOWS
        bRet = false;
        HINSTANCE hKernelDll = (HINSTANCE)dlopen("kernel32.dll", RTLD_NOW);

        if (hKernelDll)
        {
                // 'CreateHardLink()' is only available from Win2K onwards.
                if (NULL != dlsym(hKernelDll, "CreateHardLinkA"))
                        bRet = true;

                dlclose(hKernelDll);
        }
#endif
        // Other OS's could be accommodated here

        return (bRet);
}


//***************************************************************
//
//      realpath()
//
// Emulates POSIX realpath() using Win32 _fullpath().
//
//      Returns:
//
//    On Success: A pointer to the resolved (absolute) path
//    On Failure: NULL
//
LIBPBD_API char* PBD_APICALLTYPE
realpath (const char *original_path, char resolved_path[_MAX_PATH+1])
{
char *pRet = NULL;
bool bIsSymLink = 0; // We'll probably need to test the incoming path
                     // to find out if it points to a Windows shortcut
                     // (or a hard link) and set this appropriately.
        if (bIsSymLink)
        {
                // At the moment I'm not sure if Windows '_fullpath()' is directly
                // equivalent to POSIX 'realpath()' - in as much as the latter will
                // resolve the supplied path if it happens to point to a symbolic
                // link ('_fullpath()' probably DOESN'T do this but I'm not really
                // sure if Ardour needs such functionality anyway). Therefore we'll
                // possibly need to add that functionality here at a later date.
        }
        else
        {
                char temp[(MAX_PATH+1)*6]; // Allow for maximum length of a path in UTF8 characters

                // POSIX 'realpath()' requires that the buffer size is at
                // least PATH_MAX+1, so assume that the user knew this !!
                pRet = _fullpath(temp, Glib::locale_from_utf8(original_path).c_str(), _MAX_PATH);
                if (NULL != pRet)
                        strcpy(resolved_path, Glib::locale_to_utf8(temp).c_str());
        }

        return (pRet);
}


//***************************************************************
//
//      opendir()
//
// Creates a pointer to a DIR structure, appropriately filled in
// and ready to begin a directory search iteration.
//
//      Returns:
//
//    On Success: Pointer to a (heap based) DIR structure
//    On Failure: NULL
//
LIBPBD_API DIR* PBD_APICALLTYPE
opendir (const char *szPath)
{
wchar_t wpath[PATH_MAX+1];
unsigned int rc;
DIR *pDir = 0;

        errno = 0;

        if (!szPath)
                errno = EFAULT;

        if ((!errno) && ('\0' == szPath[0]))
                errno = ENOTDIR;

        // Determine if the given path really is a directory

        if (!errno)
                if (0 == MultiByteToWideChar (CP_UTF8, 0, (LPCSTR)szPath, -1, (LPWSTR)wpath, sizeof(wpath)))
                        errno = EFAULT;

        if ((!errno) && ((rc = GetFileAttributesW(wpath)) == -1))
                errno = ENOENT;

        if ((!errno) && (!(rc & FILE_ATTRIBUTE_DIRECTORY)))
                // Error. Entry exists but not a directory. */
                errno = ENOTDIR;

        if (!errno)
        {
                // Allocate enough memory to store DIR structure, plus
                // the complete directory path originally supplied.
                pDir = (DIR *)malloc(sizeof(DIR) + strlen(szPath) + strlen("\\") + strlen ("*"));

                if (!pDir)
                {
                        // Error - out of memory
                        errno = ENOMEM;
                }
        }

        if (!errno)
        {
                // Create the search expression
                strcpy(pDir->dd_name, szPath);

                // Add a backslash if the path doesn't already end with one
                if (pDir->dd_name[0] != '\0' &&
                        pDir->dd_name[strlen(pDir->dd_name) - 1] != '/' &&
                        pDir->dd_name[strlen(pDir->dd_name) - 1] != '\\')
                {
                        strcat (pDir->dd_name, "\\");
                }

                // Add the search pattern
                strcat(pDir->dd_name, "*");

                // Initialize handle to -1 so that a premature closedir()
                // doesn't try to call _findclose() on it.
                pDir->dd_handle = (-1);

                // Initialize the status
                pDir->dd_stat = 0;

                // Initialize the dirent structure. 'ino' and 'reclen' are invalid under Win32
                // and 'name' simply points at the appropriate part of the findfirst_t struct.
                pDir->dd_dir.d_ino = 0;
                pDir->dd_dir.d_reclen = 0;
                pDir->dd_dir.d_namlen = 0;
                strcpy(pDir->dd_dir.d_name, pDir->dd_dta.name);

                return (pDir);  // Succeeded
        }

        if (pDir)
                free (pDir);
        return (DIR *) 0; // Failed
}


//***************************************************************
//
//      readdir()
//
// Return a pointer to a dirent struct, filled with information
// about the next entry in the directory.
//
//      Returns:
//
//    On Success: A pointer to the supplied DIR's 'dirent' struct
//    On Failure: NULL
//
LIBPBD_API struct dirent* PBD_APICALLTYPE
readdir (DIR* pDir)
{
int old_errno = 0;
errno = 0;

        // Check for valid DIR struct
        if (!pDir)
                errno = EFAULT;

        if ((strcmp(pDir->dd_dir.d_name, pDir->dd_dta.name)) && (!errno))
                // The structure does not seem to be set up correctly
                errno = EINVAL;
        else
        {
                if (pDir->dd_stat < 0)
                {
                        // We have already returned all files in this directory
                        // (or the structure has an invalid dd_stat).
                        return (struct dirent *)0;
                }
                else if (pDir->dd_stat == 0)
                {
                        // We haven't started the search yet.
                        // Start the search
                        pDir->dd_handle = _findfirst (Glib::locale_from_utf8(pDir->dd_name).c_str(), &(pDir->dd_dta));

                        if (pDir->dd_handle == -1)
                                // The directory is empty
                                pDir->dd_stat = -1;
                        else
                                pDir->dd_stat = 1;
                }
                else
                {
                        // Do not return ENOENT on last file in directory
                        old_errno = errno;

                        // Get the next search entry
                        if (_findnext (pDir->dd_handle, &(pDir->dd_dta)))
                        {
                                // We are off the end or otherwise error
                                errno = old_errno;
                                _findclose (pDir->dd_handle);
                                pDir->dd_handle = -1;
                                pDir->dd_stat = -1;
                        }
                        else
                                // Update to indicate the correct status number
                                pDir->dd_stat++;
                }

                if (pDir->dd_stat > 0)
                {
                        // We successfully got an entry. Details about the file are
                        // already appropriately filled in except for the length of
                        // file name.
                        strcpy(pDir->dd_dir.d_name, pDir->dd_dta.name);
                        pDir->dd_dir.d_namlen = strlen (pDir->dd_dir.d_name);
                        return (&pDir->dd_dir); // Succeeded
                }
        }

        return (struct dirent *) 0; // Failed
}


//***************************************************************
//
//      closedir()
//
// Frees the resources allocated by opendir().
//
//      Returns:
//
//    On Success: 0
//    On Failure: -1
//
LIBPBD_API int PBD_APICALLTYPE
closedir (DIR *pDir)
{
int rc = 0;

        errno = 0;

        if (!pDir)
                errno = EFAULT;
        else
        {
                if ((-1) != pDir->dd_handle)
                        rc = _findclose (pDir->dd_handle);

                // Free the DIR structure
                free (pDir);

                return rc; // Succeeded
        }

        return (-1); // Failed
}

//***************************************************************
//
//      mkstemp()
//
// Emulates Linux mkstemp() using Win32 _mktemp() and _open() etc.
//
//      Returns:
//
//    On Success: A file descriptor for the opened file.
//    On Failure: (-1)
//
LIBPBD_API int PBD_APICALLTYPE
mkstemp (char *template_name)
{
int ret = (-1);
char *szFileName;
char szTempPath[PATH_MAX+100]; // Just ensure we have plenty of buffer space

        if (NULL != (szFileName = _mktemp(template_name)))
        {
                if (0 != ::GetTempPathA(sizeof(szTempPath), szTempPath))
                {
                        strcat(szTempPath, szFileName);
                        ret = _open(szTempPath, (_O_CREAT|_O_BINARY|_O_TEMPORARY|_O_RDWR|_O_TRUNC), _S_IWRITE);
                }
        }

        return (ret);
}


//***************************************************************
//
//      ntfs_link()
//
// Emulates Linux link() using Win32 CreateHardLink()(NTFS only).
//
//      Returns:
//
//    On Success: Non-zero.
//    On Failure: Zero (call 'GetLastError()' to retrieve info)
//
LIBPBD_API int PBD_APICALLTYPE
ntfs_link (const char *existing_filepath, const char *link_filepath)
{
int ret = 1; // 'ERROR_INVALID_FUNCTION'
bool bValidPath = false;

        // Make sure we've been sent a valid input string
        if (existing_filepath && link_filepath)
        {
                std::string strRoot = existing_filepath;

                if ((1 < strRoot.length()) && ('\\' == existing_filepath[0]) && ('\\' == existing_filepath[1]))
                {
                        int slashcnt = 0;

                        // We've been sent a network path. Convert backslashes to forward slashes temporarily.
                        std::transform(strRoot.begin(), strRoot.end(), strRoot.begin(), invert_backslash);

                        // Now, if there are less than four slashes, add a fourth one or abort
                        std::string::iterator iter = strRoot.begin();
                        while ((slashcnt < 4) && (iter != strRoot.end()))
                        {
                                if ('/' == (*iter))
                                        slashcnt++;

                                ++iter;
                        }

                        if (slashcnt > 2)
                        {
                                // If only 3 slashes were counted, add a trailing slash
                                if (slashcnt == 3)
                                        strRoot += '/';

                                // Now find the position of the fourth slash
                                iter = strRoot.begin();
                                int charcnt = 0;
                                for (slashcnt=0; slashcnt<4;)
                                {
                                        charcnt++;

                                        if ('/' == (*iter))
                                                slashcnt++;

                                        if (++iter == strRoot.end())
                                                break;
                                }

                                strRoot.resize(charcnt);
                                bValidPath = true;
                        }
                }
                else
                {
                        // Assume a standard Windows style path
                        if (1 < strRoot.length() && (':' == existing_filepath[1]))
                        {
                                // Convert backslashes to forward slashes temporarily.
                                std::transform(strRoot.begin(), strRoot.end(), strRoot.begin(), invert_backslash);

                                if (2 == strRoot.length())
                                        strRoot += '/';

                                if ('/' == strRoot[2])
                                {
                                        strRoot.resize(3);
                                        bValidPath = true;
                                }
                        }
                }

                if (bValidPath)
                {
                        char szFileSystemType[_MAX_PATH+1];

                        // Restore the original backslashes
                        std::transform(strRoot.begin(), strRoot.end(), strRoot.begin(), invert_forwardslash);

                        // Windows only supports hard links for the NTFS filing
                        // system, so let's make sure that's what we're using!!
                        if (::GetVolumeInformationA(strRoot.c_str(), NULL, 0, NULL, NULL, NULL, szFileSystemType, _MAX_PATH+1))
                        {
                                std::string strRootFileSystemType = szFileSystemType;
                                std::transform(strRootFileSystemType.begin(), strRootFileSystemType.end(), strRootFileSystemType.begin(), ::toupper);
#if (_WIN32_WINNT >= 0x0500)
                                if (0 == strRootFileSystemType.compare("NTFS"))
                                {
                                        if (TestForMinimumSpecOS()) // Hard links were only available from Win2K onwards
                                                if (0 == CreateHardLinkA(link_filepath, existing_filepath, NULL))
                                                {       // Note that the above API call cannot create a link to a directory, so
                                                        // should we also be checking that the supplied path was actually a file?
                                                        ret = GetLastError();
                                                }
                                                else
                                                        SetLastError(ret = 0); // 'NO_ERROR'
                                }
                                else
                                {
                                        ret = 4300; // 'ERROR_INVALID_MEDIA'
                                }
#endif
                        }
                }
                else
                        ret = 123; // 'ERROR_INVALID_NAME'
        }
        else
                ret = 161; // 'ERROR_BAD_PATHNAME'

        if (ret)
        {
                SetLastError(ret);
                return (-1);
        }
        else
                return (0);
}


//***************************************************************
//
//      ntfs_unlink()
//
// Emulates Linux unlink() using Win32 DeleteFile()(NTFS only).
//
//      Returns:
//
//    On Success: Non-zero.
//    On Failure: Zero (call 'GetLastError()' to retrieve info)
//
LIBPBD_API int PBD_APICALLTYPE
ntfs_unlink (const char *link_filepath)
{
int ret = 1; // 'ERROR_INVALID_FUNCTION'
bool bValidPath = false;

        // Make sure we've been sent a valid input string
        if (link_filepath)
        {
                std::string strRoot = link_filepath;

                if ((1 < strRoot.length()) && ('\\' == link_filepath[0]) && ('\\' == link_filepath[1]))
                {
                        int slashcnt = 0;

                        // We've been sent a network path. Convert backslashes to forward slashes temporarily.
                        std::transform(strRoot.begin(), strRoot.end(), strRoot.begin(), invert_backslash);

                        // Now, if there are less than four slashes, add a fourth one or abort
                        std::string::iterator iter = strRoot.begin();
                        while ((slashcnt < 4) && (iter != strRoot.end()))
                        {
                                if ('/' == (*iter))
                                        slashcnt++;

                                ++iter;
                        }

                        if (slashcnt > 2)
                        {
                                // If only 3 slashes were counted, add a trailing slash
                                if (slashcnt == 3)
                                        strRoot += '/';

                                // Now find the position of the fourth slash
                                iter = strRoot.begin();
                                int charcnt = 0;
                                for (slashcnt=0; slashcnt<4;)
                                {
                                        charcnt++;

                                        if ('/' == (*iter))
                                                slashcnt++;

                                        if (++iter == strRoot.end())
                                                break;
                                }

                                strRoot.resize(charcnt);
                                bValidPath = true;
                        }
                }
                else
                {
                        // Assume a standard Windows style path
                        if (1 < strRoot.length() && (':' == link_filepath[1]))
                        {
                                // Convert backslashes to forward slashes temporarily.
                                std::transform(strRoot.begin(), strRoot.end(), strRoot.begin(), invert_backslash);

                                if (2 == strRoot.length())
                                        strRoot += '/';

                                if ('/' == strRoot[2])
                                {
                                        strRoot.resize(3);
                                        bValidPath = true;
                                }
                        }
                }

                if (bValidPath)
                {
                        char szFileSystemType[_MAX_PATH+1];

                        // Restore the original backslashes
                        std::transform(strRoot.begin(), strRoot.end(), strRoot.begin(), invert_forwardslash);

                        // Windows only supports hard links for the NTFS filing
                        // system, so let's make sure that's what we're using!!
                        if (::GetVolumeInformationA(strRoot.c_str(), NULL, 0, NULL, NULL, NULL, szFileSystemType, _MAX_PATH+1))
                        {
                                std::string strRootFileSystemType = szFileSystemType;
                                std::transform(strRootFileSystemType.begin(), strRootFileSystemType.end(), strRootFileSystemType.begin(), ::toupper);
#if (_WIN32_WINNT >= 0x0500)
                                if (0 == strRootFileSystemType.compare("NTFS"))
                                        if (TestForMinimumSpecOS()) // Hard links were only available from Win2K onwards
                                                if (0 == DeleteFileA(link_filepath))
                                                        ret = GetLastError();
                                                else
                                                        ret = 0; // 'NO_ERROR'
#endif
                        }
                }
                else
                        ret = 123; // 'ERROR_INVALID_NAME'
        }
        else
                ret = 161; // 'ERROR_BAD_PATHNAME'

        if (ret)
        {
                SetLastError(ret);
                return (-1);
        }
        else
                return (0);
}

}  // namespace PBD


//***************************************************************
//
//      dlopen()
//
// Emulates POSIX dlopen() using Win32 LoadLibrary().
//
//      Returns:
//
//    On Success: A handle to the opened DLL
//    On Failure: NULL
//
LIBPBD_API void* PBD_APICALLTYPE
dlopen (const char *file_name, int mode)
{
        // Note that 'mode' is ignored in Win32
        return(::LoadLibraryA(Glib::locale_from_utf8(file_name).c_str()));
}


//***************************************************************
//
//      dlclose()
//
// Emulates POSIX dlclose() using Win32 FreeLibrary().
//
//      Returns:
//
//    On Success: A non-zero number
//    On Failure: 0
//
LIBPBD_API int PBD_APICALLTYPE
dlclose (void *handle)
{
        return (::FreeLibrary((HMODULE)handle));
}


//***************************************************************
//
//      dlsym()
//
// Emulates POSIX dlsym() using Win32 GetProcAddress().
//
//      Returns:
//
//    On Success: A pointer to the found function or symbol
//    On Failure: NULL
//
LIBPBD_API void* PBD_APICALLTYPE
dlsym (void *handle, const char *symbol_name)
{
        // First test for RTLD_DEFAULT and RTLD_NEXT
        if ((handle == 0/*RTLD_DEFAULT*/) || (handle == ((void *) -1L)/*RTLD_NEXT*/))
        {
                return 0; // Not yet supported for Win32
        }
        else
                return (::GetProcAddress((HMODULE)handle, symbol_name));
}

#define LOCAL_ERROR_BUF_SIZE 1024
static char szLastWinError[LOCAL_ERROR_BUF_SIZE];
//***************************************************************
//
//      dlerror()
//
// Emulates POSIX dlerror() using Win32 GetLastError().
//
//      Returns:
//
//    On Success: The translated message corresponding to the
//                last error
//    On Failure: NULL (if the last error was ERROR_SUCCESS)
//
LIBPBD_API char* PBD_APICALLTYPE
dlerror ()
{
        DWORD dwLastErrorId = GetLastError();
        if (ERROR_SUCCESS == dwLastErrorId)
                return 0;
        else
        {
                if (0 == FormatMessage(
                                        FORMAT_MESSAGE_FROM_SYSTEM,
                                        NULL,
                                        dwLastErrorId,
                                        0,
                                        szLastWinError,
                                        LOCAL_ERROR_BUF_SIZE,
                                        0))
                {
                        sprintf(szLastWinError, "Could not decipher the previous error message");
                }

                // POSIX dlerror() seems to reset the
                // error system, so emulate that here
                SetLastError(ERROR_SUCCESS);
        }

        return(szLastWinError);
}

#endif  // COMPILER_MSVC