Unable to create DLLs: Getting DLL "is not a valid Win32 application" - c++

Question

As the title says, I can't create a simple DLL. I'm using VS 2017 Community Edition Version 15.8.0. Here is the .dll code:
#include "stdafx.h"
#include "InvWin32App.h"
#include "$StdHdr.h"
void Prc1()
{
printf("ran procedure 1\n");
}
Here is the code for the header, per the MS way to do things:
#ifdef INVWIN32APP_EXPORTS
#define INVWIN32APP_API __declspec(dllexport)
#else
#define INVWIN32APP_API __declspec(dllimport)
#endif
#ifdef __cplusplus
extern "C" {
#endif
INVWIN32APP_API void Prc1();
#ifdef __cplusplus
}
#endif
Here is the driver code: (Update: The driver program is an .exe program.)
#include "pch.h"
#include "InvWin32App.h"
int main()
{
Prc1();
}
It can't get any simpler than this. I get the following error message box when I try to run the code:
Unable to start program
program name.dll
program name.dll is not
a valid Win32 application
I can create .exe programs okay. I also got the error earlier this morning when I was running VS 2017 Version 15.7.5. Upgrading VS didn't do any good. I also tried to compile these as .c programs, but it didn't make any difference.
I had this problem on a couple occasions creating .exe programs using VS 2015. I don't recall what I did, but the problem disappeared. Any help would be appreciated.
TIA.

Answer 1

Right click the project in your solution explorer that is the project for the executable and click "Set as startup project."
Note that "is not a valid Win32 application" is not a compile error or a link error, it is the message you get when you tried to debug something that is not executable.
You can only start executables. Executables consume dlls. These should be two seperate projects with two sets of corresponding project settings.

Answer 2

I doubt that you are using a 32 bit dll. If you have your 64-bit Windows OS then you must have 64 bit version of this dll too. Sometimes, even you have 64-bit dll already then it could not run, so try the other version of this dll i.e. 32 bit version of this dll.
Along with this, make a small change in your unicurse.py file too.
PFB the code to add:
import ctypes
pdlib = ctypes.CDLL("pdcurses.dll")
though this line of code is somewhere inside some condition, but bringing on top will help you to check, if the dll has been loaded or not.

Answer 3

For any one joining the party at this time, I found that this error is caused when you try to run a 32bit dll using a 64bit python.
Now I won't go into the details as to why that won't work as above responses clearly describes that, but there are 2 solutions for this.
Install and 32bit python and use that to communicate with the dll.
Interprocess communication using the msl-loadlib library documentation
I used the second step which seemed more sustainable. The steps I am using below can be found in the documentation link above.
First is to create a server module that communicates with the 32 bit module
#server.py
from msl.loadlib import Server32
class Server(Server32):
# the init takes mandatory host and port as arguments
def __init__(self, host, port, **kwargs):
# using windll since this application is being run in windows, other options such as cdll exists
# this assumes that the dll file is in the same directory as this file
super(Server, self).__init__('tresdlib.dll', 'windll', host, port)
# define a function that is to be called with the required arguments
def fsl_command(self, com, doc):
#the server32 exposes the loaded dll as lib, which you can then use to call the dll functions and pass the required arguments
return self.lib.FSL_Command(com,doc)
Then we create a client module, that sends python requests to the server module
#client.py
from msl.loadlib import Client64
class Client(Client64):
def __init__(self):
# pass the server file we just created in module32=, the host am using is localhost, leave port as none for self assigning
super(Client, self).__init__(module32='server', host="127.0.0.1", port=None)
# define a function that calls the an existing server function and passes the args
def fsl_command(self, com, doc):
return self.request32('fsl_command', com, doc)
We are going to run this in a terminal but you can choose to call in another application
>>> from client import Client
>>> c = Client()
>>> c.fsl_command(arg1,arg2)