Raxpedia

jeudi 26 février 2015

Create a DLL using C - CL.EXE Compiler

16:14
Just to create a DLL file using C language, you need to create three files :

  1. Library header (.h)
  2. Library Source (.c) : will be compiled to build the DLL
  3. Main Program (.c) : this is the source of the program that will use the DLL
In the next example we will create a simple program that use calculating functions (+ , - , * and / ) that are included in a DLL.

1 - Library Header: mydll.h
In this step we have to create a mydll.h file that we will declare in the functions that we will use in our program.

__declspec(dllexport) float add_func(float x, float y);
__declspec(dllexport) float sub_func(float x, float y);
__declspec(dllexport) float mul_func(float x, float y);
__declspec(dllexport) float div_func(float x, float y);


2 - Library Source: mydll.c
In this file, we must include the "Library Header" then define our functions like this example :

#include "mydll.h"

float add_func(float x, float y)
{
    return x + y;
}
float sub_func(float x, float y)
{
    return x - y;
}
float mul_func(float x, float y)
{
    return x * y;
}
float div_func(float x, float y)
{
    if(y != 0)
        return x / y;
    else
        return -1; //Returns -1 if y == 0
} 

3 - Library Source: calcul.c
This is program that will use the dll, we must include the needed headers including "Library Header", we will use <stdio.h> header and "mydll.h" then use the function

#include <stdio.h>
#include "mydll.h"

int main()
{
    float x, y;
    printf("Enter two numbers:");
    scanf("%f %f", &x, &y);
    printf("ADD: %f\n", add_func(x, y) );
    printf("SUB: %f\n", sub_func(x, y) );
    printf("MUL: %f\n", mul_func(x, y) );
    printf("DIV: %f\n", div_func(x, y) );
    return 0;
}

Now we are going to compile all of that using CL compiler

DLL Compiling:

To compile the DLL using CL Compiler, we need the name of "Library Source", in our example the name of that is mydll.c:

cl /LD mydll.c

the /LD flag is the flag that create the DLL with other needed files.

You can see that "mydll.dll" generated successfully with other files.

EXE Compiling :

We almost complished our mission.
Now you need to compile the "calcul.c" to build our program, using this command :
cl calcul.c mydll.lib
You can see that we have used "mydll.lib" that help us to build the program.


Now you can keep just calcul.exe and mydll.dll then remove other files .

Finally run the program:


SETUP CL.EXE COMPILER - MICROSOFT VISUAL STUDIO

14:28
Firstly, you must have Microsoft Visual Studio Already installed.

Open cmd and run this batch file:
"C:\Program Files\Microsoft Visual Studio 10.0\VC\vcvarsall.bat"
then write:

  1. echo %PATH% and add the shown content to "PATH" in Environment Variables for your account.
  2. echo %INCLUDE% and add the shown content to "INCLUDE" in Environment Variables for your account.
  3. echo %LIB% and add the shown content to "LIB" in Environment Variables for your account.
  4. echo %LIBPATH% and add the shown content to "LIBPATH" in Environment Variables for your account.
Now, to test if the operation done, close current cmd and open another one then write:
cl.exe

You must get something like this :

If an error happened or you have trouble, then just you need to type
"C:\Program Files\Microsoft Visual Studio 10.0\VC\vcvarsall.bat"
every time you have opened the cmd (command prompt).
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