Define in C++ new environment variable and use it in bat file

Question

It is very simple, I want to define a new environment variable in C++ using SetEnvironmentVariable, and then call a bat file that use it. This is my c++ code;

PROCESS_INFORMATION processInformation = { 0 };
STARTUPINFO startupInfo = { 0 };

SetEnvironmentVariable("GSDebbugingDir", "Hello");

BOOL result = CreateProcess(NULL,
                                    "dummy.bat"),
                                    NULL,
                                    NULL,
                                    FALSE,
                                    CREATE_NO_WINDOW,
                                    NULL,
                                    NULL,
                                    &startupInfo,
                                    &processInformation);

And my dummy.bat file is :

@echo off    
echo GSDebbugingDir = %GSDebbugingDir%    
if defined GSDebbugingDir mkdir c:\temp\dummy    
pause

But this didn't out the value of GSDebbugingDir variable. What is the problem?

Answer 1

CreateProcess documentation says:

To run a batch file, you must start the command interpreter ; set lpApplicationName to cmd.exe and set lpCommandLine to the following arguments: /c plus the name of the batch file.

Which makes sense because a .bat file by itself is not an executable module by itself. But, contrary to what the doc says the following code worked for me with UseApplicationName NOT #defined, ie with "cmd.exe" placed into commandLine

Also, to see the output of the bat file you probably want to remove that CREATE_NO_WINDOW flag

//#define UseApplicationName
#ifdef UseApplicationName
TCHAR  commandLine[] = _T(" /c dummy.bat");
#else
TCHAR  commandLine[] = _T("cmd.exe /c dummy.bat");
#endif

BOOL result = CreateProcess(
#ifdef UseApplicationName
    _T("cmd.exe"),
#else
    NULL,
#endif
    commandLine,
    NULL,
    NULL,
    FALSE,
    0, //CREATE_NO_WINDOW,
    NULL,
    NULL,
    &startupInfo,
    &processInformation);

BTW pay attention that

The Unicode version of this function, CreateProcessW, can modify the contents of this string. Therefore, this parameter cannot be a pointer to read-only memory (such as a const variable or a literal string).