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Dynamic-link Library - mIRC
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mIRC allows programs to make calls to various dynamic-link libraries (DLLs) designed to work with mIRC. The main reason you would want to do this is that processing information in a DLL can be far faster than doing so in a mIRC script, so for intensive data processing a DLL would be more efficient.

Note: mIRC also supports calling COM objects, for calling non-standard DLLs.

Using a Dll[edit]


/dll <filename> <procname> [data]
/dll -u <filename>
$dll(<filename>, <procname>, [data])
$dllcall(<filename>, <alias>, <procname>, [data])


  • -u - Unloads the dll


  • <filename> - The filename for the dll you wish to use.
  • <procname> - The name of the function/procedure you wish to call.
  • [data] - The optional parameters for the function/procedure.
  • <alias> - If you use $dllcall, it calls the function asynchronously, meaning that the code won't halt, $dllcall won't return a value. Instead, mIRC calls the specified <alias> when the function finishes.

Creating a Dll[edit]

Note: We won't deal with how to create a dll in details, the scripter here must be familiar with dll creation already.

The exported functions must have the following function prototype:

#include <windows.h>
int __stdcall funcName(HWND mWnd, HWND aWnd, char *data, char *parms, BOOL show, BOOL nopause);
  • mWnd - The handle of the main mIRC window.
  • aWnd - The handle of the window in which the command is being issued, this might not be the currently active window if the command is being called by a remote script.
  • data - This is a buffer you can write to if you want mIRC to perform a command or to return a value from a $dll call (remember that $dllcall do not return a value by design even if you fill this buffer),
  • parms - For a better handling of command execution, this is a buffer which can be filled if you are filling the 'data' buffer with a command. mIRC will fill the variable $1- with this value, which you can include in the command in 'data'. The examples shows how to use it.

Note: Both 'data' and 'params' are allocated with the Line Length Limit of mIRC, 4150 characters on mIRC 7.34 at the time of writting this.

  • show - This Bool value is FALSE if a dot '.' has been used to make the command (/.dll) quiet.
  • nopause - This Bool value is TRUE if mIRC is in a critical routine, meaning that you must not stop the processing in mIRC (long while loop for example).

These functions must use the stdcall calling convention. (This is also the standard calling convention for all other Microsoft Win32 API functions.)

Note on C++ Dll and stdcall[edit]

If you are making a C++ dll, you need to use the extern "C" directive on all the function that you want to export (all the function called from mIRC including the LoadDll and UnloadDll routine), which indicates the function has "C" linkage as opposed to "C++".

The interesting difference is that C linkage does not use "mangling" when exporting your function, an operation which rename your functions with additional information to help the linking process.

extern "C" int __stdcall funcName(HWND mWnd, HWND aWnd, char *data, char *parms, BOOL show, BOOL nopause);

However, the __stdcall standard convention implies a mangling operation which extern "C" does not override.

To solve this problem, most of the linker will allow you to provide a .def file, where you can define the real name of your exported functions

Creating a file for that can be annoying, on Visual Studio you can use a #pragma directive to do that on the fly, the examples illustrate this

Note: If you use GCC Gnu to compile, it has something similar to __stdcall, __attribute__((stdcall)).

Return value[edit]

The function returns an integer, this value indicates what mIRC should do:

  • 0 - Means that mIRC should /halt processing.
  • 1 - Means that mIRC should continue processing.
  • 2 - Means that you have filled the 'data' variable with a command which mIRC should perform, you can also fill the "parms" variable with the parameters to use, if any.
  • 3 - Means that the DLL has filled the data variable with the result that $dll() as an identifier should return.

Note: this only applies when using $dll or /dll.

Keeping a Dll loaded[edit]

By default a DLL is unloaded immediately after you make the /dll or $dll()/$dllcall call.

You can keep a DLL loaded by including a LoadDll() routine in your DLL, which mIRC calls the first time you load the DLL:

void __stdcall LoadDll(LOADINFO*);

typedef struct {
   DWORD  mVersion;
   HWND   mHwnd;
   BOOL   mKeep;
   BOOL   mUnicode;
  • mVersion - Contains the mIRC version number in the low and high words.
  • mHwnd - Contains the window handle to the main mIRC window.
  • mKeep - Is set to TRUE by default, indicating that mIRC will keep the DLL loaded after the call. You can set mKeep to FALSE to make mIRC unload the DLL after the call (which is how previous mIRCs worked)
  • mUnicode - If set to true, indicates that text is in unicode as opposed to ansi (default). This means the data passed from/to the dll is in utf16, the prototype of the function becomes:
int __stdcall funcName(HWND mWnd, HWND aWnd, wchar *data, wchar *parms, BOOL show, BOOL nopause);
Notice the difference for data and parms, which are now of the type wchar instead of char

Unloading the Dll[edit]

mIRC will automatically unload a DLL if it is not used for ten minutes, or when mIRC exits.

You can define an UnloadDll() routine in your DLL which mIRC will call when unloading a DLL to allow it to clean up:

int __stdcall UnloadDll(int mTimeout);

The mTimeout value can be:

  • 0 - UnloadDll() is being called due to a DLL being unloaded with /dll -u.
  • 1 - UnloadDll() is being called due to a DLL not being used for ten minutes. You can return return 0 to keep the DLL loaded, or 1 to allow it to be unloaded.
  • 2 - UnloadDll() is being called due to a DLL being unloaded when mIRC exits.


Example 1 : Using Visual studio (C++)[edit]

This example use a non-unicode project. We don't use a .def file but a #pragma comment to export functions.

We use the LoadDll and UnloadDll routine to start/stop a communication with mIRC using SendMessage().

#include <cstdio>
#include <windows.h>
#define WM_MCOMMAND WM_USER + 200
#define WM_MEVALUATE WM_USER + 201

//__stdcall cause mangling of the form _yourfunctionname@N where N is the number of bytes for all the parameters
//we use #pragma to redefine the name of the exported functions, if we don't do that, you can still call the dll using the name "_youfunctionname@24" ;)
//the prototype of our function always takes 6 parameters, each taking 4 bytes 6*4=24
//the prototype for LoadDll and UnloadDll takes one parameter, a structure which is 4 bytes
#pragma comment(linker, "/EXPORT:usingSM=_usingSM@24")
#pragma comment(linker, "/EXPORT:LoadDll=_LoadDll@4")
#pragma comment(linker, "/EXPORT:UnloadDll=_UnloadDll@4")
#pragma comment(linker, "/EXPORT:simple_example=_simple_example@24")
#pragma comment(linker, "/EXPORT:average_example=_average_example@24")
#pragma comment(linker, "/EXPORT:more_example=_more_example@24")
#pragma comment(linker, "/EXPORT:from_event=_from_event@24")

HANDLE file;
LPSTR str;

extern "C" int __stdcall simple_example(HWND mWnd, HWND aWnd, CHAR *data, char *parms, BOOL show, BOOL nopause)
        //we fill data with a simple string we want to return
	strcpy(data,"simple string");
	//we return 3 indicating $dll should return the value we copied in 'data'
	return 3;

extern "C" int __stdcall average_example(HWND mWnd, HWND aWnd, CHAR *data, char *parms, BOOL show, BOOL nopause)
        //we fill data with a command we want mirc to execute
	strcpy(data,"/echo -a é");
	//we return 2 indicating mIRC should execute the command in 'data'.
	return 2;

extern "C" int __stdcall more_example(HWND mWnd, HWND aWnd, CHAR *data, char *parms, BOOL show, BOOL nopause)
        //we fill data with a command we want mirc to execute
	strcpy(data,"/echo -a $1-");
	//we return 2 indicating mIRC should execute the command in 'data', and set $1- to parms.
	return 2;

extern "C" int __stdcall from_event(HWND mWnd, HWND aWnd, CHAR *data, char *parms, BOOL show, BOOL nopause)

	SendMessage(mWnd, WM_MEVALUATE, MAKEWPARAM(0, atoi(data)), 0);
	return 3;

extern "C" int __stdcall usingSM(HWND mWnd, HWND aWnd, CHAR *data, char *parms, BOOL show, BOOL nopause)
	//send //echo -s Hello world to mIRC
	strcpy(str,"//echo -a Hello world");
	SendMessage(mWnd, WM_MCOMMAND, 1 , 0);
	//Ask mIRC to evaluate and send back the result
	strcpy(str,"m $+ $upper(irc)");
	SendMessage(mWnd, WM_MEVALUATE, 0, 0);
	//Copy the result of "m $+ $upper(irc)" into data and we return 3 indicating $dll returns what 'data' contains
	return 3;

 typedef struct {
   DWORD  mVersion;
   HWND   mHwnd;
   BOOL   mKeep;
   BOOL   mUnicode;

extern "C" void __stdcall LoadDll(LOADINFO *load) {
	file = CreateFileMapping(INVALID_HANDLE_VALUE,NULL,PAGE_READWRITE,0,4096, "mIRC");
	str = (LPSTR) MapViewOfFile(file, FILE_MAP_ALL_ACCESS, 0, 0, 0);
	//after MapViewOfFile(), 'str' is where you write to but also is the result of each call with WM_MEVALUATE:

extern "C" int __stdcall  UnloadDll(int mTimeout) {
	//if dll is unloaded because mIRC exit or dll -u is used, we clean up, otherwise we prevent the unloading by returning 0.
	if (mTimeout != 1) CloseHandle(file);
	return 0;

Use $dll(yourdll.dll,simple_example), which will return "simple string".

Use $dll(yourdll.dll,average_example) or /dll yourdll.dll average_example, this will execute "/echo -a é" in mIRC 7.x, because the project is not unicode, the two bytes é are sent as ascii, mIRC 7.x will correctly decode that as utf8. On mIRC 6.x (you would need to remove the mUnicode variable in the LOADINFO structure), this would display the two bytes.

If you set the mUnicode variable to TRUE on mIRC 7.x in the LoadDll function and if you set your project to use unicode (in visual studio: project properties > configuration properties > general > character set), this would correctly show the two bytes as well.

Use $dll(yourdll.dll,more_example) or /dll yourdll.dll more_example, this will fill $1- from data with the value from parms and execute the final "//echo -a test".

Use $dll(yourdll.dll,from_event,$eventid) inside an event where $nick exists, this will use SendMessage() to evaluate $nick from the event context and fill data with that value, returned by $dll.

Use $dll(yourdll.dll,usingSM), which will use SendMessage() to execute a command in mIRC, it will also evaluate a line of code and return the result in $dll().

Example 2 : Using GNU GCC on Windows (C)[edit]

//To compile, use:
//gcc -c -O3 reverse.c ; gcc -shared --export-all-symbols -o reverse.dll -O3 reverse.o
//reverse.c content:
#include <windows.h>
#include <string.h>
int __attribute__((stdcall))
reverse(HWND mWnd, HWND aWnd, char *data, char *parms, BOOL show, BOOL nopause)
      char *l = *data ? data + strlen(data) - 1 : data;
      char *p = parms;
      while ((*p++ = *l--));
      strcpy(data, "/echo -s ");
      strcat(data+8, parms);
      return 2;

Use dll "reverse.dll" reverse <text>.