C++ LPTSTR problem calling CreateProcessAsUser with getenv

I am trying to call function CreateProcessAsUser. Passing constant string is fine. Trying to pick up an Environment variable using char* getenv(const char name) is causing me a problem.

If I use the following, notepad.exe will run.

CreateProcessAsUser(hTokenDup, _T("c:\\windows\\notepad.exe"), 
                    _T("c:\\windows\\notepad.exe"), NULL, NULL, FALSE,
                    dwCreationFlag, pEnvironment, NULL, &si, &pi);

However, if I use the following nothing runs.

CreateProcessAsUser(hTokenDup, _T("MyAppName"), 
                    (LPTSTR)getenv("MYENVVAR"), NULL, NULL, FALSE,
                    dwCreationFlag, pEnvironment, NULL, &si, &pi);

Have I specified the getenv and (LPTSTR) correctly?

I have tried using user and system environment vars containing c:\\windows\\notepad.exe and c:\windows\notepad.exe.

Thanks!

Solution

The third parameter, lpCommandLine is LPTSTR which means it must be writeable memory. You need to copy the command line into a writeable string before calling CreateProcessAsUser.

The documentation for getenv states:

It is not safe to modify the value of the environment variable using the returned pointer.

You therefore cannot pass this as the lpCommandLine parameter of CreateProcessAsUser.

Your first call to CreateProcessAsUser appears to be wrong too since you also are not passing writeable memory for lpCommandLine.

Of course it's most likely that your immediate problem is that you are mixing ANSI and Unicode. If your app is Unicode then you need to call _wgetenv, or _tgetenv if you really do want to target both ANSI and Unicode from the same source. But make sure you copy it into a writeable buffer before passing it on.

Finally, as Adam commented, every time you write a cast, there is a strong possibility that you are making a mistake.