How to use CALL function in Excel?

The `CALL` function in Excel is a powerful but rarely used feature that allows you to call external procedures from dynamic link libraries (DLLs) or code resources from Macintosh code resource files. It’s primarily used by advanced users who need to interface with external code or perform very specific tasks that are not possible with native Excel functions. Here’s how to use it:

Syntax

CALL(text, [text], argument1, argument2, ...)

text1: This is the name of the DLL or code resource file.
text2: This is the name of the procedure within the DLL or code resource. This argument is optional but usually required.
argument1, argument2, …: These are the arguments that you pass to the procedure. The number and type of arguments depend on the procedure you are calling.

Important Notes

Security: Using the `CALL` function can pose security risks because it executes code from outside Excel. Be sure you trust the source of any DLLs or code resources you’re interfacing with.
Availability: This function is part of Excel’s XLM macro language and may not be available in newer Excel versions unless macros are fully enabled.
Complexity: It requires detailed knowledge of the DLL or code resource you’re working with, particularly the functions you intend to call.
Compatibility: As `CALL` is associated with Excel 4.0 macros (XLM), it is not compatible with VBA (Visual Basic for Applications), which is the newer macro language. However, VBA is a safer and more modern alternative for interfacing with external code.

Example Usage

Here’s a hypothetical example of using `CALL`:

Suppose you have a DLL named `MyDLL.dll` with a procedure `AddNumbers` that takes two arguments and returns their sum.

=CELL("MyDLL.dll", "AddNumbers", 3, 7)

This would call the `AddNumbers` function within `MyDLL.dll` and pass the arguments `3` and `7` to it.

Using VBA Instead

For those not comfortable with using the CALL function, using VBA to create custom functions to interact with DLLs might be a better approach. VBA provides a `Declare` statement to define DLL procedures and is generally safer and more manageable.

Example of a VBA Declaration:

Declare Function AddNumbers Lib "MyDLL.dll" (ByVal x As Long, ByVal y As Long) As Long

Function Usage in VBA:

Sub CallAddNumbers()
    Dim result As Long
    result = AddNumbers(3, 7)
    MsgBox "The result is " & result
End Sub

In summary, while the `CALL` function can be used for highly specialized tasks, it is complex and carries certain risks. For most users, VBA offers a more practical and safer solution for accessing external procedures. Always ensure your sources are secure, and consider the maintainability of your Excel solutions before using `CALL`.

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