This is part of Win16 API which allow to create versions of program from one source code to run under OS/2 and Win16. Under OS/2 program can be running under Win-OS/2 if program is Windows NE executable, and with help on Windows Libraries for OS/2, if it is OS/2 NE executable. Here is a WLO to OS/2 API mapping draft

MessageBox

Brief

The MessageBox function creates, displays, and operates a message box. The message box contains an application-defined message and title, plus any combination of predefined icons and push buttons.

Syntax

int MessageBox(HWND hWnd, LPCSTR lpText, LPCSTR lpCaption, UINT uType);

Parameters

hWnd - Handle to the owner window of the message box to be created. If this parameter is NULL, the message box has no owner window.

lpText - Pointer to a null-terminated string containing the message to be displayed. If the string consists of more than one line, you can separate the lines using a carriage return and/or linefeed character between each line.

lpCaption - Pointer to a null-terminated string used for the dialog box title. If this parameter is NULL, the default title “Error” is used.

uType - Contains a set of bit flags that determine the content and behavior of the dialog box. This parameter can be a combination of flags from the following groups:

Buttons:

MB_ABORTRETRYIGNORE - Contains Abort, Retry, and Ignore buttons.

MB_OK - Contains one push button: OK (default).

MB_OKCANCEL - Contains OK and Cancel buttons.

MB_RETRYCANCEL - Contains Retry and Cancel buttons.

MB_YESNO - Contains Yes and No buttons.

MB_YESNOCANCEL - Contains Yes, No, and Cancel buttons.

Icons:

MB_ICONEXCLAMATION / MB_ICONWARNING - Exclamation-point icon.

MB_ICONINFORMATION / MB_ICONASTERISK - Information icon (i in a circle).

MB_ICONQUESTION - Question-mark icon.

MB_ICONSTOP / MB_ICONERROR / MB_ICONHAND - Stop-sign icon.

Default Button:

MB_DEFBUTTON1 - First button is default (default).

MB_DEFBUTTON2 - Second button is default.

MB_DEFBUTTON3 - Third button is default.

Modality:

MB_APPLMODAL - Application-modal (default). User must respond to the message box before continuing work in the current window.

MB_SYSTEMMODAL - System-modal (topmost). All applications are suspended until user responds.

MB_TASKMODAL - Task-modal. Similar to MB_APPLMODAL but used when the calling application has no window handle.

Other:

MB_SETFOREGROUND - Message box becomes the foreground window.

MB_TOPMOST - Message box is placed above all non-topmost windows.

Return Code

The function returns zero if there is not enough memory to create the message box. If the call succeeds, the return value is one of the following menu-item values:

IDABORT - Abort button was selected.

IDCANCEL - Cancel button was selected.

IDIGNORE - Ignore button was selected.

IDNO - No button was selected.

IDOK - OK button was selected.

IDRETRY - Retry button was selected.

IDYES - Yes button was selected.

Notes

The system supports only a limited number of message boxes simultaneously.

When using the MB_SYSTEMMODAL flag, the message box appears on top of all windows and is typically used for critical errors requiring immediate user attention.

If a message box is created without an owner window (hWnd = NULL), it behaves as an independent window.

The message box is modal and does not return control until the user closes it by pressing a button.

Example Code

C Binding

#include <windows.h> int PASCAL WinMain(HANDLE hInstance, HANDLE hPrevInstance, LPSTR lpCmdLine, int nCmdShow) { // Simple information message box MessageBox(NULL, "Hello, world! This is a message from Janus.", "Win16 Example", MB_OK | MB_ICONINFORMATION); // Question message box with Yes/No/Cancel int result = MessageBox(NULL, "Do you want to save changes?", "Confirmation", MB_YESNOCANCEL | MB_ICONQUESTION | MB_DEFBUTTON1); // Handle the result if (result == IDYES) { MessageBox(NULL, "You chose Yes", "Result", MB_OK | MB_ICONINFORMATION); } else if (result == IDNO) { MessageBox(NULL, "You chose No", "Result", MB_OK | MB_ICONINFORMATION); } else if (result == IDCANCEL) { MessageBox(NULL, "You chose Cancel", "Result", MB_OK | MB_ICONWARNING); } // Error message example MessageBox(GetActiveWindow(), "File not found. Please check the path.", "Error", MB_OK | MB_ICONSTOP | MB_SYSTEMMODAL); return 0; }

MASM Binding

; Example for MASM (Microsoft Macro Assembler) ; Assemble with: MASM /MX program.asm ; Link with: LINK program.obj,,,libw.lib,, .MODEL LARGE .386 INCLUDE windows.inc .DATA msg_hello DB "Hello, world!", 0 cap_hello DB "Greeting", 0 msg_question DB "Continue operation?", 0 cap_question DB "Question", 0 msg_yes DB "You pressed Yes", 0 msg_no DB "You pressed No", 0 msg_cancel DB "Operation cancelled", 0 cap_result DB "Result", 0 .CODE START PROC FAR ; Initialize push ds pop ax xor ax, ax ; Simple message box push MB_OK OR MB_ICONINFORMATION ; uType push OFFSET cap_hello ; lpCaption push OFFSET msg_hello ; lpText push 0 ; hWnd = NULL call MessageBox ; Question message box push MB_YESNOCANCEL OR MB_ICONQUESTION ; uType push OFFSET cap_question ; lpCaption push OFFSET msg_question ; lpText push 0 ; hWnd = NULL call MessageBox ; Check result (result is in AX) cmp ax, IDYES je show_yes cmp ax, IDNO je show_no cmp ax, IDCANCEL je show_cancel jmp exit_program show_yes: push MB_OK OR MB_ICONINFORMATION push OFFSET cap_result push OFFSET msg_yes push 0 call MessageBox jmp exit_program show_no: push MB_OK OR MB_ICONINFORMATION push OFFSET cap_result push OFFSET msg_no push 0 call MessageBox jmp exit_program show_cancel: push MB_OK OR MB_ICONWARNING push OFFSET cap_result push OFFSET msg_cancel push 0 call MessageBox exit_program: ; Exit program mov ax, 4C00h int 21h START ENDP END START

See also

MessageBoxIndirect

MessageBeep

DialogBox

DialogBoxParam

CreateDialog

FlashWindow

GetActiveWindow

SetActiveWindow

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Module manager	GETVERSION GETMODULEHANDLE GETMODULEUSAGE GETMODULEFILENAME GETPROCADDRESS MAKEPROCINSTANCE FREEPROCINSTANCE GETINSTANCEDATA CATCH THROW GETCODEHANDLE LOADLIBRARY
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Task Scheduler	GetCurrentTask Yield SetPriority
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Debugging	FatalExit
File I/O	_lopen _lcreat _llseek _lread _lwrite _lclose OpenFile GetTempFileName GetTempDrive
Registry	RegOpenKey RegCreateKey RegCloseKey RegDeleteKey RegSetValue RegQueryValue RegEnumKey
Dialogs	MessageBox