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c++winapiparametersnullcreateprocess

C++ Winapi CreateProcess issue with command line

I'm using CreateProcess this way:

resultCreate = CreateProcess(Command, CommandLine, NULL, NULL, FALSE, 0, NULL, NULL, &si, &pi);

//"Command" contains the executable file to execute
//"CommandLine" contains the parameters to pass to that executable

The parameters are the following:

Param1: "C:\Users\myuser\Desktop\file.dll"
Param2: "file" (module name)
Param3: " " (blank)

So the full CommandLine string would be:

"C:\Users\myuser\Desktop\file.dll" file " "

CreateProcess runs the executable successfully and applies the first two parameters, but when reaches the third one, it throws error

The specified process could not be found.
Function " " could not be called, due to " " doesn't exist in the DLL "(null)"

How can I pass the desired parameters correctly?

Solution

  • When both lpApplicationName and lpCommandLine are used, you need to include the executable path as the first parameter of your lpCommandLine value, even though you are specifying the executable path in the lpApplication value. The lpCommandLine is passed as-is to the spawned process, and most RTLs (especially C-based RTLs, but others as well) expect the first command-line parameter to be the executable path since that is how command-line consoles operate. This is even mentioned in the CreateProcess() documentation:

    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.

    This is also covered in MSDN Support:

    INFO: Understanding CreateProcess and Command-line Arguments

    Behavior of CreateProcess() When Creating a 32-bit Process

    Case 1:

    If the ApplicationName parameter is passed and the CommandLine parameter is NULL, then the ApplicationName parameter is also used as the CommandLine. This does not mean that you can pass additional command-line parameters in ApplicationName string. For example, the following call will fail with a "File Not Found" error: 

    CreateProcess( "c:\\MyApp.exe Param1 Param2", NULL, ... )

    Case 2:

    On the other hand, if the CommandLine parameter is non-NULL and the ApplicationName parameter is NULL, then the API attempts to extract the application name from the CommandLine parameter.

    Case 3:

    The flexibility of the CreateProcess() function (and a possible point of confusion) arises when you pass a valid string pointer to both the ApplicationName and CommandLine parameters. This allows you to specify the application to be executed as well as the complete command line that is passed to the application. One might assume that the command line passed to the created application is a composite of the ApplicationName and CommandLine parameters, but this is not the case. As a result, a process created by CreateProcess can receive a value other than its .exe name as its "argv[0]" parameter. The following is an example of a call to CreateProcess that produces this "abnormal" behavior: 

    CreateProcess( "c:\\MyApp.exe", "Param1 Param2 Param3", ...)

    MyApp's arguments will be as follow: 

    argv[0] == "Param1"
argv[1] == "Param2"
argv[2] == "Param3"

    NOTE: ANSI specifications require that argv[0] should be equal to the application name, but CreateProcess gives the calling application the flexibility to override this rule for 32-bit processes.

    Case #3 applies to your situation.

    Use something like this instead:

    std::string Command = "<exe path>";
std::string CommandLine = "\"" + Command + "\" <parameters>";

// std::string::c_str() returns a const pointer. The first parameter
// of CreateProcessA() is const, but the second parameter must be a
// non-const pointer to writable memory, because CreateProcessW() can
// modify the data...
//
resultCreate = CreateProcessA(Command.c_str(), &CommandLine[0], ...);


    std::wstring Command = L"<exe path>";
std::wstring CommandLine = L"\"" + Command + L"\" <parameters>";

// std::wstring::c_str() returns a const pointer. The first parameter
// of CreateProcessW() is const, but the second parameter must be a
// non-const pointer to writable memory, because CreateProcessW() can
// modify the data...
//
resultCreate = CreateProcessW(Command.c_str(), &CommandLine[0], ...);

    Alternatively, omit lpApplicationName and specify the complete command line to lpCommandLine only:

    std::string CommandLine = "\"<exe path>\" <parameters>";
resultCreate = CreateProcessA(NULL, &CommandLine[0], ...);


    std::wstring CommandLine = L"\"<exe path>\" <parameters>";
resultCreate = CreateProcessW(NULL, &CommandLine[0], ...);