jeudi 26 février 2015

Create a DLL using C - CL.EXE Compiler

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

Library header (.h)
Library Source (.c) : will be compiled to build the DLL
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.