Calling native functions in dynamic link libraries

Epson RC+ 8.0 allows you to call native functions in Dynamic Link Libraries (DLLs).

This is used for complicated arithmetic processing and call for a native function of an external device.

To call the native DLL function, use a Declare statement which is a function definition command from the SPEL+ program and write a function call as normal.

For details, refer to the following manual.

"SPEL+ Language Reference - Declare"

Sample of calling a native DLL

By using a development tool such as Microsoft Visual Studio 2019, you can create a native DLL that can be called from SPEL+. Here, it uses Visual Studio 2019 as a sample to create a function that executes the arithmetic operator.

Step 1: Decide on variable type for a native DLL

You need to plan the data type to use for transferring with the native DLL in the Epson RC+ 8.0. Correspondence table for the Epson RC+ 8.0 data type and the C/C++ variable type is shown below. You cannot use the C/C++ byte type and structure because the Epson RC+ 8.0 has no correspond data for them.

Data correspondence

Epson RC+ 8.0	C/C++
Boolean	short
Byte	short
Short	short
Integer	short
Long	int
Real	float
Double	double
String	char [256] * Null included

Step 2: Create a native DLL

Start Visual Studio 2019.

Select the "Create a new project" on the start window.
[Create a new project] dialog box will appear.
1. Select “Windows Desktop Wizard” from the project template list shown on the right of dialog box.
2. Click the [Next] button.
Start the Windows Desktop Wizard.
1. Type in a name for a project in the [Project name] box. (Here types in "MyCalculator".)
2. Click the [Create] button.
Set the project options.
1. Select the “Dynamic Link Library (.dll)” in the [Application type].
2. Check the [Export symbols] box in the [Additional options:].
3. Click the [OK] button.

A simple example of function “fnMyCalculator” will be created in MyCalculator.cpp. Add a function MyArithmetic which executes the arithmetic operator to this file.

MYCALCULATOR_API float MyArithmetic(short value1, short value2, char * kind )
{
  if ( !strcmp(kind, "add") )
  {
    return (float)(value1 + value2);
  }
  else if ( !strcmp(kind, "sub") )
  {
    return (float)(value1 - value2);
  }
  else if ( !strcmp(kind, "mul") )
  {
    return (float)(value1 * value2);
  }
  else if ( !strcmp(kind, "div") )
  {
    return (float)(value1) / (float)(value2);
  }
  else
  {
    strcat_s(kind, 10, " NG");
    return 0;
  }
}

Export a function to enable it to be called from SPEL+.
1. Select Visual Studio 2019 menu-[Project]-[Add New Item]. The [Add New Item] dialog box will appear.
2. Select the [Visual C ++]-[Code] in the tree on the left.
3. Select “Module-Definition File (.def)” from the project template list shown on the center of dialog box.
4. Type in a file name in the [Name:]. (Here types in "MyCalculator.def" as a file name.)
5. Click the [Add (A)] button.
6. Register “fnMyCalculator function” and “MyArithmetic function” to the created “MyCalculator.def” file.
```
LIBRARY "MyCalculator"
EXPORTS
fnMyCalculator
MyArithmetic
```
Build the project and create the DLL. Select [Win32] as a solution platform for Visual Studio 2019. Then, select Visual Studio 2019 menu-[Build]-[Build MyCalculator]. DLL will be successfully created if no error occurs.

KEY POINTS

In Epson RC+ 8.0, 64 bit native DLL is not available. When using a DLL created with a version older than Visual Studio 2015, it is necessary to install the runtime corresponding to that version in advance.

Step 3: Call the DLL function from SPEL+

KEY POINTS

You can now try your DLL function from SPEL+. Before you call your function from the Epson RC+ 8.0, you must debug it and check thoroughly if it can work without errors. In case that error occurs (such as system error) in the native function, the Epson RC+ 8.0 will not work normally.

Copy the created MyCalculator.dll to the Epson RC+ 8.0 project folder (e.g. C:\EpsonRC80\projects\dllcall).

Define a DLL function which executes the arithmetic operator in the SPEL+ program and write a function call for MyArithmetic in Function main.

Declare MyArithmetic, "MyCalculator.dll"(value1 As Integer, value2 As Integer, ByRef calc$ As String) As Real
Function main
  Real result;
  String calc$

  calc$ = "add"
  result = MyArithmetic(1, 2, ByRef calc$);
  Print "1+2=", Str$(result)
  calc$ = "sub"
  result = MyArithmetic(1, 2, ByRef calc$);
  Print "1-2=", Str$(result)
  calc$ = "mul"
  result = MyArithmetic(1, 2, ByRef calc$);
  Print "1*2=", Str$(result)
  calc$ = "div"
  result = MyArithmetic(1, 2, ByRef calc$);
  Print "1/2=", Str$(result)
Fend

Build and execute the project. The following result will be displayed.
```
1+2=3
1-2=-1
1*2=2
1/2=0.5
```

KEY POINTS

Before you build the project, be sure to copy the native DLL to the project folder without fail. If you fail, a warning or error will occur.

Please note the dependency of the DLL when using a third party DLL as a native DLL. If the dependent DLL does not exist in the project folder or the folder set in the environment variable PATH of Windows, a warning or error will occur.

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