why argv in createProcess() is different from normal c++ program - c++

Question

this is my code, and i found the first output is "thisProgram.exe"
and the second output is "a".
why?
i read the doc in msdn, however i don't quite clear why the argv[0] can be "a", is there something different in windows when using createProcess. Could someone please tell me the difference from lpApplicationName and lpCommandline? thanks
int main( int argc, char *argv[] ) {
cout << argv[0] << endl;
STARTUPINFO si;
PROCESS_INFORMATION pi;
ZeroMemory(&si, sizeof(si));
si.cb = sizeof(si);
ZeroMemory(&pi, sizeof(pi));
// Start the child process.
if (!CreateProcess("thisProgram.exe", // No module name (use command line)
"a b c", // 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) // Pointer to PROCESS_INFORMATION structure
) {
printf("CreateProcess failed (%d).\n", GetLastError());
return 1;
}
// Wait until child process exits.
WaitForSingleObject(pi.hProcess, INFINITE);
// Close process and thread handles.
CloseHandle(pi.hProcess);
CloseHandle(pi.hThread);
return 0;
}

Answer 1

CreateProcess passes the second argument (the command line) to the new process as its command line. CreateProcess will not prepend the module name. If you want the application name to appear as argv[0] you must repeat the application name in the command line argument.
The documentation says it like this:
If both lpApplicationName and lpCommandLine are non-NULL, the null-terminated string pointed to by lpApplicationName specifies the module to execute, and the null-terminated string pointed to by lpCommandLine specifies the command line. The new process can use GetCommandLine to retrieve the entire command line. Console processes written in C can use the argc and argv arguments to parse the command line. Because argv[0] is the module name, C programmers generally repeat the module name as the first token in the command line.
It's generally simplest to pass NULL for the application name, and for the command line pass the application name and the arguments concatenated together.