Question about a valid file path

Question

I am using the following code to create a file, but it always failed with error code 123 (the path syntax is not valid).

The strange thing is: path_ok is always ok, but path_err always failed with 123. And after the failure, the buffer that path_err points to is cleared.

Could anyone shed some light on me? I have checked the memory of the 2 pointers, and their contents seems to be identical.

Many thanks.

 WCHAR *pDumpFileName = ComposeDumpFileName();
 WCHAR *path_ok = _T("d:\\myapp_Utopia_2010-11-15_04-22-05.dmp");
 WCHAR *path_err = pDumpFileName;
 ::wprintf(pDumpFileName);
 HANDLE hFile = ::CreateFileW( pDumpFileName, GENERIC_READ | GENERIC_WRITE, 
  0, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL ); 

The ComposeDumpFileName() function is like this:

WCHAR* ComposeDumpFileName(void)
{
 // get the time
    SYSTEMTIME sys_time;
    ::GetSystemTime(&sys_time);

    // get the computer name
    WCHAR computer_name[MAX_COMPUTERNAME_LENGTH + 1];
    DWORD computer_name_len = ARRAYSIZE(computer_name);
 ::GetComputerNameW(computer_name, &computer_name_len);

    // build the filename: APPNAME_COMPUTERNAME_DATE_TIME.DMP
    WCHAR dump_file_path[MAX_PATH];

 ::swprintf_s(dump_file_path, ARRAYSIZE(dump_file_path), 
        _T("d:\\myapp_%s_%04u-%02u-%02u_%02u-%02u-%02u.dmp"), 
        computer_name, sys_time.wYear, sys_time.wMonth, sys_time.wDay,
        sys_time.wHour, sys_time.wMinute, sys_time.wSecond);

 return dump_file_path;
}

Update

In my above code, when I execute the following code:

WCHAR *pDumpFileName = ComposeDumpFileName();

After the ComposeDumpFileName returned, its stack frame is invalid, however, its local variable WCHAR dump_file_path[MAX_PATH] still exists on the stack. So this explains why I can still see its content though the stack space for it is invalid already.

Then I execute the following statement:

     ::wprintf(pDumpFileName);
     HANDLE hFile = ::CreateFileW( pDumpFileName, GENERIC_READ | GENERIC_WRITE, 
      0, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL ); 

The wprintf() and CreateFileW() has their own stack frames. Though in the debugger, I found that wprintf()'s stack frame didn't destroy the memory content pointed by the pDumpFileName, the CreateFileW could have, so it complains about a invalid path syntax.

This is my current understanding, please correct me if I am wrong.

Thanks.

Answer 1

One major problem with your code is the buffer you are returning is on the stack and this is a big no no:

 // build the filename: APPNAME_COMPUTERNAME_DATE_TIME.DMP 
 WCHAR dump_file_path[MAX_PATH]; 

Either change it to be a static:

 // build the filename: APPNAME_COMPUTERNAME_DATE_TIME.DMP 
 static WCHAR dump_file_path[MAX_PATH]; 

or pass the buffer into the function.