C Multiple processes: Program crashes while creating child process - windows

Question

I am trying to create a child process with the following command:
STARTUPINFO si;
PROCESS_INFORMATION pi;
ZeroMemory( &si, sizeof(si) );
si.cb = sizeof(si);
ZeroMemory( &pi, sizeof(pi) );
CreateProcess( NULL, // No module name (use command line)
NULL, // Command line
NULL, // Process handle not inheritable
NULL, // Thread handle not inheritable
FALSE, // Set handle inheritance to FALSE
0, // No creation flags
NULL, // Use parent's environment block
NULL, // Use parent's starting directory
&si, // Pointer to STARTUPINFO structure
&pi );
It crashes over here and I am not sure why.
Now my original process takes command line parameters, so do I have to pass them here also? If so then since I am not creating child process from int main() so can I do the following:
LPTSTR szCmdline = TEXT("nmctest -s TS -r DMR -tlLDMR");
Then pass szCmdline inside CreateProcess()?
Can someone please help me why this is crashing?

Answer 1

Your code is failing because you are passing NULL for both lpApplicationName and lpCommandLine. You must pass a value for at least one of them. The documentation makes that clear.
It looks like you have also attempted to pass a value to lpCommandLine. But you have passed a non-modifiable string literal. Again the documentation makes it clear that is not allowed. Pass a pointer to memory that can be modified.
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). If this parameter is a constant string, the function may cause an access violation.
You can meet that requirement like this:
TCHAR szCmdline[] = _T("nmctest -s TS -r DMR -tlLDMR");
Personally, I see no need for TCHAR in this day and age. Surely you aren't still writing programs for Windows 98? I would do it like so:
wchar_t szCmdline[] = L"nmctest -s TS -r DMR -tlLDMR";
The other possible failure vector in your code is the STARTUPINFO parameter. Make sure that you have initialised that correctly. The most simply way to do that is like so:
STARTUPINFO si = {0};
si.cb = sizeof(si);
But you might like to add a call to GetStartupInfo.
STARTUPINFO si = {0};
si.cb = sizeof(si);
GetStartupInfo(&si);