Make a C# call to "C" DLL function(api) work.

See more:

C

C#

Windows

DLL

API

Okay OriginalGriff, RSVP

I have written a C# front-end program, in which calls a bunch of DLL "C" functions(API's). and the communications between the two parts has been great.
But recently, I was working on the program and must have done something wrong, and now I can't call a DLL function period.

So now, every time I try to run the this program, I get the following errors:
* Exception thrown: 'System.BadImageFormatException' in textlib.exe
* An attempt was made to load a program with an incorrect format.
(Exception from HRESULT: 0x8007000B)
It seems like when I attempt to call a DLL function(API) from within the C# program, the following error/exception(s) (above) surfaces.

I sure could use some help OriginalGriff

What have you tried? is is in the screen below. Again Thanks.

What I have tried:

Okay OriginalGriff, RSVP

SOME NEEDED EXAMPLES, PLEASE;

Here in my C# program,(below)are some examples of "C#"'s import DLL function call declarations,
referencing an external DLL file to be used, with referenced API calls.

*** In the C# sharp environment:
 [DllImport("textlibrary.dll", CallingConvention = CallingConvention.Cdecl)]
             public static extern int MM_MAXNUMBEROFTEXTFORMATS(ref int numfmts);

 [DllImport("textlibrary.dll", CallingConvention = CallingConvention.Cdecl)] 
             public static extern int MM_ISVDATE(StringBuilder bufferdate);  

 [DllImport("textlibrary.dll", CallingConvention = CallingConvention.Cdecl)] public static extern 
       int MM_APPSTESTSRUN(StringBuilder testrundate, int ifmtid, int idpassval, ref int iostat);
 
 DllImport("kernel32.dll")] static extern uint GetSystemDirectory(
             [Out] StringBuilder lpBuffer, uint uSize);

 [DllImport("Advapi32.dll")] public static extern bool GetUserName
             (StringBuilder lpBuffer, ref int nSize);

 [DllImport("user32.dll", SetLastError = true, CharSet = CharSet.Auto)] public static extern uint 
            GetWindowModuleFileName(IntPtr hwnd, StringBuilder lpszFileName, uint cchFileNameMax);

*** In the "C" DLL environment:
/////              and "C" function declarations. 
#include <time.h>
//// https://docs.microsoft.com/en-us/cpp/build/walkthrough-creating-and-using-a-dynamic-link-library-cpp?view=msvc-170
#pragma once   //// I'm using implicit linking, .lib file - linker file input. 
#ifdef TEXTLIBRARY_EXPORTS
#define TEXTLIBRARY_API __declspec(dllexport)
#else
#define TEXTLIBRARY __declspec(dllimport)
#endif
extern "C" {  //// this declaration hopefully should make each routine names are managled free. 
    TEXTLIBRARY_API int MM_JDECYYDDDxOperation(int pdopcode, char* passdjdedate8, 
                     char* rtnhumandate, int* iostatx);
    TEXTLIBRARY_API int MM_AXDYs(char* testitem, int addnumdays, int* irtnerrval);
    TEXTLIBRARY_API int MM_TheISONotationforms(char* xpdtheccyyform11, int  imee, int* iostatzs1);
    TEXTLIBRARY_API int MM_ListOutAllUserNames(char* wfilename260, int* filesw, int* ierrsw) ;

  }  

*----------------*
Now for the question(s), please...
I have a program that consists of two parts(a C# program(the front end) and a DLL File [with a
bunch of DLL function(APIs)) calls] that worked quite well together for quite a while, but
has since recently stopped and no more communications were achieved. I cannot figure out
why/how/what it has stopped and to understand why. It seems like I may have done
something, but I don't remember doing it and why. I've noticed some of the forms that have
worked before stopped, have a few errors.
So now, every time I try to run the this program, I get the following errors:
* Exception thrown: 'System.BadImageFormatException' in textlib.exe
* An attempt was made to load a program with an incorrect format.
(Exception from HRESULT: 0x8007000B)
It seems like when I attempt to call a DLL function(API) from within the C# program, the
following error/exception(s) (above) surfaces.
So how can I get these two entities to communicate with each other again? Successfully?

I've checked out most of your Site's error-questions and solutions relating to this problem,
and it seems like my programs are in sync and are following the same rules as given in the
solutions provided. The C# program and the dll file, each compiles successfully, and the
IDE knows where the DLL file is located and shows it. It seems like the C# program would
run ok by itself, without calling any of the DLL functions(APIs).

I can use these "C" dll file function(APIs) calls in other "C" programs and they work ok.
But I need these " 'C' dll file function(APIs) calls" to be used in my C# program also.

Could someone or ones help me out, in finding what is going on and what I did wrong and then
achieve successful communication between these two parts. Cause right now, I'm at a
stand-still. How can I "link" a DLL to a C-sharp program or am I doing it right?

But anyrate, Thanks for any help.