Visual C++ Undesired Result When UsingCreateProcess() - visual-c++

Question

I'm building a Visual C++ console application and I need to execute another program located in same directory as the console application. I used CreateProcess() to start it.
VOID startup(LPCTSTR lpApplicationName, LPSTR args)
{
// additional information
STARTUPINFO si;
PROCESS_INFORMATION pi;
// set the size of the structures
ZeroMemory(&si, sizeof(si));
si.cb = sizeof(si);
ZeroMemory(&pi, sizeof(pi));
// start the program up
CreateProcess(lpApplicationName, // the path
args, // 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
);
WaitForSingleObject(pi.hProcess, INFINITE);
CloseHandle(pi.hProcess); // Close process and thread handles.
CloseHandle(pi.hThread);
}
Ans this is the function call-
string command = "C:\\Users\\username\\Documents\\Visual Studio 2013\\Projects\\Project\\Debug\\potrace.exe"; //the program to be executed
string arg = "-s -o \"" + libraryDir + "\\" + outputFileName + "\" -- \"" + tempDir + "\\" + tempFileName + "\""; //program arguments to be sent
char *args = new char[200];
for (int i = 0; args[i] = arg[i]; ++i); //converting std::string to char*
startup(command.c_str(), args);
The problem is that program being called produces different result when called from within the console application and when called from a command prompt. It generated an svg file but when called from application, this generated file is corrupt. If I copy the value of char *args and use it as argument at command prompt, the output file is perfect and intact.
UPDATE: on opening the generated files I noticed that it's and EPS file, not an SVG file. This is very strange because the -s in args is for generating SVG file. Also, copying the value of command.c_str() and args and executing from command prompt does produce a valid SVG image. So why is the same command producing different result when called usign CreateProcess() and from command prompt?
UPDATE: if I modify args to include the program name too i.e., potrace.exe <arguments> and call startup using startup(NULL, args) then it runs perfectly. But I would still like to know the problem in the original approach.

Answer 1

The documentation for CreateProcess says:
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.
When a C or C++ program starts, the runtime calls GetCommandLine to get the command line used to invoke the program. This is parsed to obtain the argc and argv to be passed to main.
If the program being spawned expects that the program name is in argv[0] and the "actual" arguments start with argv[1], then you must ensure that you include the program name in the lpCommandLine passed to CreateProcess so that it is present in the command line string returned by GetCommandLine in the spawned process.