In this c++ dll example we used a dlll to perform simple mathematical operation which is to convert from Celsius to Fahrenheit and vice versa





The first step is creating the dll
1 - Start new Win32 Dynamic link library and name it famo chose simple dll project the middle one
2- Open the code and add the following
__declspec(dllexport)void Fehrenhite_Celcius_converter(int n_operation, double input , double &result) ;
// we used reference here since we want to change the value of output inside the function
below #include "stdafx.h"

and at the buttom
add the following

void Fehrenhite_Celcius_converter(int n_operation, double input , double &result)
{ switch (n_operation) {
case 0 :
result= 1.8 * input +32 ;
break ;
case 1 :
result = ( ( double) 5/ (double) 9) * (input -32) ;
break ;
}
// casting needed here bec 5/9 is considered 0
break ; }
}

compile the dlll

Now start new MFC name it mydll_program dialog application and chose not to select the about box and name iy Celcius_Fehrenhite converter

3- Add the 2 static controls and 2 Edit controls a button , group box and 2 radio buttons as shown above

In the group box name it converting and in the static boxes in the properties chose caption input and for the second one chose caption output

Add member variables in the class wizards m_input for the first edit box and m_outputs for the second edit box both of type CString
Add a variable of type int integer for the first radio button m_operation
in the properties chose group

4- after compiling the dlls copy the lib and dll to dialog directory

5- In the project menu Add to projects then chose files as shown here





In the class wizard add member function for the calculate button and name it On_Conversion or anything

Add the following line at the top of the dialog class
__declspec(dllimport)void Fehrenhite_Celcius_converter(int n_operation, double input , double &result) ;
To include the dlls

put in the On_Conversion add follows


void CMydll_programDlg::On_Conversion()
{
UpdateData();
double inputs , outputs ;
inputs = atof(m_input);
// temperature input
Fehrenhite_Celcius_converter(m_operation , inputs ,outputs) ;
// m_operation represents the type of conversion
m_outputs.Format("%2.3f", outputs);
UpdateData(FALSE);
}

build and compile your program

This lesson teaches you how to make simple static dll application for more see other links in the blog