test.cpp

#define WIN32_ULTRA_LEAN
#define UNICODE
#include <Windows.h>
#include <cstdio>
#include <cstdlib>

int TestSetCurrentDirectory( const wchar_t* directory )
{
   if( !SetCurrentDirectory( directory ) )
   {
      printf( "  unable to set current directory.\n" );
      return 1;
   }

   wchar_t currentDirectory[MAX_PATH];
   if( !GetCurrentDirectory( MAX_PATH, currentDirectory ) ) exit(1);
   wprintf( L"Current directory=%s\n", currentDirectory );
}

int TestOpenFileRelative( const wchar_t* directory, const wchar_t* filename )
{
   if( !SetCurrentDirectory( directory ) )
   {
      printf( "  unable to set current directory.\n" );
      return 1;
   }

   HANDLE file = CreateFile( filename, GENERIC_READ, FILE_SHARE_READ, nullptr, OPEN_EXISTING, 0, nullptr );
   if( file == INVALID_HANDLE_VALUE )
   {
      printf( "  unable to open file.\n" );
      return 1;
   }

   char buf[4096];
   DWORD numBytesRead;
   if( !ReadFile( file, buf, sizeof(buf)-1, &numBytesRead, nullptr ) )
      return 1;
   buf[numBytesRead] = 0;
   CloseHandle( file );

   printf( "  %s\n", buf );

   return 0;
}

int main( int, char** )
{
   TestSetCurrentDirectory( L"C:\\windows" );
   TestSetCurrentDirectory( L"C:" );
   TestSetCurrentDirectory( L"C:\\" );
   TestSetCurrentDirectory( L"C:a" );
   TestSetCurrentDirectory( L"C:a" );
   TestSetCurrentDirectory( L"Z:" );
   TestSetCurrentDirectory( L"C:" );

   printf( "\n" );

   TestOpenFileRelative( L"C:", L"C:a\\b.txt" );
   TestOpenFileRelative( L"C:\\a", L"C:a\\b.txt" );
   TestOpenFileRelative( L"C:", L"C:a\\b.txt" );
   TestOpenFileRelative( L"Z:", L"C:a\\b.txt" );
   TestOpenFileRelative( L"Z:\\temp", L"C:a\\b.txt" );

   system( "PAUSE" );
   return 0;
}

// the files C:\a\b.txt and C:\a\a\b.txt exist and contain text describing their position on the file-system.

// Output:
/*
Current directory=C:\windows
Current directory=C:\windows
Current directory=C:\
Current directory=C:\a
Current directory=C:\a\a
Current directory=Z:\
Current directory=C:\

This file is C:\a\b.txt
This file is C:\a\a\b.txt
This file is C:\a\a\b.txt
This file is C:\a\b.txt
This file is C:\a\b.txt
*/