这是我的解决方案。我选择使用 Motif (OpenMotif)，因为它需要相对较少的额外库（Xm、Xt、X11）。根据消息的大小，我的实现会打开一个简单的消息框或更复杂的对话框，其中包含不可编辑、可滚动的文本（后者取自 Motif 程序员手册并适用于我的目的）。
包括文件和全局数据：
#include <Xm/Xm.h>
#include <Xm/MwmUtil.h>
#include <Xm/MainW.h>
#include <Xm/CascadeB.h>
#include <Xm/MessageB.h>
#include <Xm/RowColumn.h>
#include <Xm/Form.h>
#include <Xm/PushBG.h>
#include <Xm/LabelG.h>
#include <Xm/PanedW.h>
#include <Xm/Text.h>
#include <Xm/DialogS.h>
#include <Xm/Command.h>
static XtAppContext appShell;
确定行数和最大值的辅助函数。短信的cols：
static int MsgSize (char* pszMsg, int& nCols)
{
if (!(pszMsg && *pszMsg))
return 0;
int nRows = 1;
nCols = 0;
for (char* p = pszMsg; *p && (pszMsg = strchr (p, '\n')); nRows++, p = ++pszMsg) {
if (nCols < pszMsg - p)
nCols = pszMsg - p;
}
return nRows;
}
消息对话框关闭按钮的回调函数：
void DestroyShell (Widget widget, XtPointer clientData, XtPointer callData)
{
Widget shell = (Widget) clientData;
XtDestroyWidget (shell);
// tell the application event loop to terminate w/o terminating the application
XtAppSetExitFlag (appShell);
}
构建一个对话框，其中包含一个可滚动的、不可编辑的文本小部件和一个关闭按钮。取自 Motif 程序员手册并稍作修改（无图标，单个按钮），最小的窗口装饰）。
void XmMessageDialog (const char* pszMsg, int nRows, int nCols, bool bError)
{
Widget msgBox, pane, msgText, form, widget;
void DestroyShell(Widget, XtPointer, XtPointer);
Arg args [10];
int n = 0;
int i;
Dimension h;
// Set up a DialogShell as a popup window. Set the delete window protocol response to XmDESTROY to make sure that
// the window goes away appropriately. Otherwise, it's XmUNMAP which means it'd be lost forever, since we're not storing
// the widget globally or statically to this function.
Widget topWid = XtVaAppInitialize (&appShell, "D2X-XL", NULL, 0, &argc, argv, NULL, NULL);
XtSetArg (args [0], XmNdeleteResponse, XmDESTROY);
msgBox = XmCreateDialogShell (topWid, bError ? const_cast<char*>("Error") : const_cast<char*>("Warning"), args, 1);
XtVaGetValues (msgBox, XmNmwmDecorations, &i, NULL);
i &= ~(MWM_DECOR_ALL | MWM_DECOR_MINIMIZE | MWM_DECOR_MAXIMIZE | MWM_DECOR_MENU);
XtVaSetValues (msgBox, XmNmwmDecorations, i, NULL);
XtVaGetValues (msgBox, XmNmwmFunctions, &i, NULL);
i &= ~(MWM_FUNC_ALL | MWM_FUNC_MINIMIZE | MWM_FUNC_MAXIMIZE | MWM_FUNC_CLOSE);
XtVaSetValues (msgBox, XmNmwmFunctions, i, NULL);
// Create a PanedWindow to manage the stuff in this dialog. PanedWindow won't let us set these to 0!
XtSetArg (args [0], XmNsashWidth, 1);
// Make small so user doesn't try to resize
XtSetArg (args [1], XmNsashHeight, 1);
pane = XmCreatePanedWindow (msgBox, const_cast<char*>("pane"), args, 2);
// Create a RowColumn in the form for Label and Text widgets. This is the control area.
form = XmCreateForm (pane, const_cast<char*>("form1"), NULL, 0);
// prepare the text for display in the ScrolledText object we are about to create.
n = 0;
XtSetArg (args [n], XmNscrollVertical, True); n++;
XtSetArg (args [n], XmNscrollHorizontal, False); n++;
XtSetArg (args [n], XmNeditMode, XmMULTI_LINE_EDIT); n++;
XtSetArg (args [n], XmNeditable, False); n++;
XtSetArg (args [n], XmNcursorPositionVisible, False); n++;
XtSetArg (args [n], XmNwordWrap, True); n++;
XtSetArg (args [n], XmNvalue, pszMsg); n++;
XtSetArg (args [n], XmNrows, min (nRows, 30)); n++;
XtSetArg (args [n], XmNcolumns, min (nCols, 120)); n++;
msgText = XmCreateScrolledText (form, const_cast<char*>("help_text"), args, n);
// Attachment values must be set on the Text widget's PARENT, the ScrolledWindow. This is the object that is positioned.
XtVaSetValues (XtParent (msgText),
XmNleftAttachment, XmATTACH_FORM,
XmNtopAttachment, XmATTACH_FORM,
XmNrightAttachment, XmATTACH_FORM,
XmNbottomAttachment, XmATTACH_FORM,
NULL);
XtManageChild (msgText);
XtManageChild (form);
// Create another form to act as the action area for the dialog
XtSetArg (args [0], XmNfractionBase, 5);
form = XmCreateForm (pane, const_cast<char*>("form2"), args, 1);
// The OK button is under the pane's separator and is attached to the left edge of the form. It spreads from
// position 0 to 1 along the bottom (the form is split into 5 separate grids via XmNfractionBase upon creation).
widget = XmCreatePushButtonGadget (form, const_cast<char*>("Close"), NULL, 0);
XtVaSetValues (widget,
XmNtopAttachment, XmATTACH_FORM,
XmNbottomAttachment, XmATTACH_FORM,
XmNleftAttachment, XmATTACH_POSITION,
XmNleftPosition, 2,
XmNrightAttachment, XmATTACH_POSITION,
XmNrightPosition, 3,
XmNshowAsDefault, True,
XmNdefaultButtonShadowThickness, 1,
NULL);
XtManageChild (widget);
XtAddCallback (widget, XmNactivateCallback, DestroyShell, (XtPointer) msgBox);
// Fix the action area pane to its current height -- never let it resize
XtManageChild (form);
XtVaGetValues (widget, XmNheight, &h, NULL);
XtVaSetValues (form, XmNpaneMaximum, h, XmNpaneMinimum, h, NULL);
// This also pops up the dialog, as it is the child of a DialogShell
XtManageChild (pane);
}
消息框“确定”按钮的回调函数
void XmCloseMsgBox (Widget w, XtPointer clientData, XtPointer callData)
{
XtAppSetExitFlag (appShell);
}
决定是使用简单消息框还是高级消息框，显示它们中的任何一个，并在用户单击其关闭/确定按钮时将其删除。
void XmMessageBox (const char* pszMsg, bool bError)
{
Widget topWid;
int nRows, nCols;
nRows = MsgSize (const_cast<char*>(pszMsg), nCols);
if ((nRows > 3) || (nCols > 360))
XmMessageDialog (pszMsg, nRows, nCols, bError);
else { // use the built-in message box
topWid = XtVaAppInitialize (&appShell, "D2X-XL", NULL, 0, &argC, argv, NULL, NULL);
// setup message box text
Arg args [1];
XmString xmString = XmStringCreateLocalized (const_cast<char*>(pszMsg));
XtSetArg (args [0], XmNmessageString, xmString);
// create and label message box
Widget xMsgBox = bError
? XmCreateErrorDialog (topWid, const_cast<char*>("Error"), args, 1)
: XmCreateWarningDialog (topWid, const_cast<char*>("Warning"), args, 1);
// remove text resource
XmStringFree (xmString);
// remove help and cancel buttons
XtUnmanageChild (XmMessageBoxGetChild (xMsgBox, XmDIALOG_CANCEL_BUTTON));
XtUnmanageChild (XmMessageBoxGetChild (xMsgBox, XmDIALOG_HELP_BUTTON));
// add callback to the "close" button that signals closing of the message box
XtAddCallback (xMsgBox, XmNokCallback, XmCloseMsgBox, NULL);
XtManageChild (xMsgBox);
XtRealizeWidget (topWid);
}
XtAppMainLoop (appShell);
XtUnrealizeWidget (topWid);
XtDestroyApplicationContext (appShell);
}