Fixed bug 3804 - Message box on Windows truncates button ID

Simon Hug

I just wanted to fix a simple compiler warning in SDL_ShowMessageBox on Windows (which Sam fixed recently) and ended up finding some issues.

Attached patch fixes these issues:

- Because Windows only reports the lower 16 bits of the control identifier that was pushed, the button IDs used by SDL (C type int, most likely 32 bits) can get cut off.

- The documentation states (somewhat ambiguously) that the button ID will be -1 if the dialog was closed, but the current code sets 0. For SDL 2.1, I think this should be a return code of SDL_ShowMessageBox itself. That will free up the button ID and it seems a more appropriate place for signaling this event.

- Ampersands in controls will create mnemonics on Windows (underlined letters that, if combined with the Alt key, will push the button). I was thinking of adding a hint or flag to let the users enable it, but that might have unexpected results.

- When the size of the text gets calculated, it doesn't use the same parameters as the static control. This can cut off text or wrap it weirdly.

- On Windows, the Tab key is used to switch between control groups and sometimes between buttons in dialogs. This didn't seem to work correctly.

Attached patch also adds:

- Icons. Just the system ones that can be loaded with the ordinals IDI_ERROR, IDI_WARNING and IDI_INFORMATION.

- A button limit of 2^16 - 101.

- Some more specific error messages, but they never reach the user because how SDL_ShowMessageBox handles them if an implementation returns with an error.

src/video/SDL_video.c

@@ -3774,6 +3774,8 @@ SDL_ShowMessageBox(const SDL_MessageBoxData *messageboxdata, int *buttonid)
 
     if (!messageboxdata) {
         return SDL_InvalidParamError("messageboxdata");
+    } else if (messageboxdata->numbuttons < 0) {
+        return SDL_SetError("Invalid number of buttons");
     }
 
     current_window = SDL_GetKeyboardFocus();

src/video/windows/SDL_windowsmessagebox.c

@@ -22,6 +22,14 @@
 
 #if SDL_VIDEO_DRIVER_WINDOWS
 
+#ifdef HAVE_LIMITS_H
+#include <limits.h>
+#else
+#ifndef SIZE_MAX
+#define SIZE_MAX ((size_t)-1)
+#endif
+#endif
+
 #include "../../core/windows/SDL_windows.h"
 
 #include "SDL_assert.h"
@@ -32,6 +40,34 @@
 #define SS_EDITCONTROL  0x2000
 #endif
 
+#ifndef IDOK
+#define IDOK 1
+#endif
+
+#ifndef IDCANCEL
+#define IDCANCEL 2
+#endif
+
+/* Custom dialog return codes */
+#define IDCLOSED 20
+#define IDINVALPTRINIT 50
+#define IDINVALPTRCOMMAND 51
+#define IDINVALPTRSETFOCUS 52
+#define IDINVALPTRDLGITEM 53
+/* First button ID */
+#define IDBUTTONINDEX0 100
+
+#define DLGITEMTYPEBUTTON 0x0080
+#define DLGITEMTYPESTATIC 0x0082
+
+/* Windows only sends the lower 16 bits of the control ID when a button
+ * gets clicked. There are also some predefined and custom IDs that lower
+ * the available number further. 2^16 - 101 buttons should be enough for
+ * everyone, no need to make the code more complex.
+ */
+#define MAX_BUTTONS (0xffff - 100)
+
+
 /* Display a Windows message box */
 
 #pragma pack(push, 1)
@@ -70,15 +106,79 @@ typedef struct
     Uint8 *data;
     size_t size;
     size_t used;
+    WORD numbuttons;
 } WIN_DialogData;
 
+static SDL_bool GetButtonIndex(const SDL_MessageBoxData *messageboxdata, Uint32 flags, size_t *i)
+{
+    for (*i = 0; *i < (size_t)messageboxdata->numbuttons; ++*i) {
+        if (messageboxdata->buttons[*i].flags & flags) {
+            return SDL_TRUE;
+        }
+    }
+    return SDL_FALSE;
+}
 
 static INT_PTR MessageBoxDialogProc(HWND hDlg, UINT iMessage, WPARAM wParam, LPARAM lParam)
 {
+    const SDL_MessageBoxData *messageboxdata;
+    size_t buttonindex;
+
     switch ( iMessage ) {
+    case WM_INITDIALOG:
+        if (lParam == 0) {
+            EndDialog(hDlg, IDINVALPTRINIT);
+            return TRUE;
+        }
+        messageboxdata = (const SDL_MessageBoxData *)lParam;
+        SetWindowLongPtr(hDlg, GWLP_USERDATA, lParam);
+
+        if (GetButtonIndex(messageboxdata, SDL_MESSAGEBOX_BUTTON_RETURNKEY_DEFAULT, &buttonindex)) {
+            /* Focus on the first default return-key button */
+            HWND buttonctl = GetDlgItem(hDlg, (int)(IDBUTTONINDEX0 + buttonindex));
+            if (buttonctl == NULL) {
+                EndDialog(hDlg, IDINVALPTRDLGITEM);
+            }
+            PostMessage(hDlg, WM_NEXTDLGCTL, (WPARAM)buttonctl, TRUE);
+        } else {
+            /* Give the focus to the dialog window instead */
+            SetFocus(hDlg);
+        }
+        return FALSE;
+    case WM_SETFOCUS:
+        messageboxdata = (const SDL_MessageBoxData *)GetWindowLongPtr(hDlg, GWLP_USERDATA);
+        if (messageboxdata == NULL) {
+            EndDialog(hDlg, IDINVALPTRSETFOCUS);
+            return TRUE;
+        }
+
+        /* Let the default button be focused if there is one. Otherwise, prevent any initial focus. */
+        if (GetButtonIndex(messageboxdata, SDL_MESSAGEBOX_BUTTON_RETURNKEY_DEFAULT, &buttonindex)) {
+            return FALSE;
+        }
+        return TRUE;
     case WM_COMMAND:
+        messageboxdata = (const SDL_MessageBoxData *)GetWindowLongPtr(hDlg, GWLP_USERDATA);
+        if (messageboxdata == NULL) {
+            EndDialog(hDlg, IDINVALPTRCOMMAND);
+            return TRUE;
+        }
+
         /* Return the ID of the button that was pushed */
-        EndDialog(hDlg, LOWORD(wParam));
+        if (wParam == IDOK) {
+            if (GetButtonIndex(messageboxdata, SDL_MESSAGEBOX_BUTTON_RETURNKEY_DEFAULT, &buttonindex)) {
+                EndDialog(hDlg, IDBUTTONINDEX0 + buttonindex);
+            }
+        } else if (wParam == IDCANCEL) {
+            if (GetButtonIndex(messageboxdata, SDL_MESSAGEBOX_BUTTON_ESCAPEKEY_DEFAULT, &buttonindex)) {
+                EndDialog(hDlg, IDBUTTONINDEX0 + buttonindex);
+            } else {
+                /* Closing of window was requested by user or system. It would be rude not to comply. */
+                EndDialog(hDlg, IDCLOSED);
+            }
+        } else if (wParam >= IDBUTTONINDEX0 && (int)wParam - IDBUTTONINDEX0 < messageboxdata->numbuttons) {
+            EndDialog(hDlg, wParam);
+        }
         return TRUE;
 
     default:
@@ -89,15 +189,30 @@ static INT_PTR MessageBoxDialogProc(HWND hDlg, UINT iMessage, WPARAM wParam, LPA
 
 static SDL_bool ExpandDialogSpace(WIN_DialogData *dialog, size_t space)
 {
+    /* Growing memory in 64 KiB steps. */
+    const size_t sizestep = 0x10000;
     size_t size = dialog->size;
 
     if (size == 0) {
-        size = space;
-    } else {
-        while ((dialog->used + space) > size) {
-            size *= 2;
+        /* Start with 4 KiB or a multiple of 64 KiB to fit the data. */
+        size = 0x1000;
+        if (SIZE_MAX - sizestep < space) {
+            size = space;
+        } else if (space > size) {
+            size = (space + sizestep) & ~(sizestep - 1);
         }
+    } else if (SIZE_MAX - dialog->used < space) {
+        SDL_OutOfMemory();
+        return SDL_FALSE;
+    } else if (SIZE_MAX - (dialog->used + space) < sizestep) {
+        /* Close to the maximum. */
+        size = dialog->used + space;
+    } else if (size < dialog->used + space) {
+        /* Round up to the next 64 KiB block. */
+        size = dialog->used + space;
+        size += sizestep - size % sizestep;
     }
+
     if (size > dialog->size) {
         void *data = SDL_realloc(dialog->data, size);
         if (!data) {
@@ -175,7 +290,7 @@ static void Vec2ToDLU(short *x, short *y)
 }
 
 
-static SDL_bool AddDialogControl(WIN_DialogData *dialog, WORD type, DWORD style, DWORD exStyle, int x, int y, int w, int h, int id, const char *caption)
+static SDL_bool AddDialogControl(WIN_DialogData *dialog, WORD type, DWORD style, DWORD exStyle, int x, int y, int w, int h, int id, const char *caption, WORD ordinal)
 {
     DLGITEMTEMPLATEEX item;
     WORD marker = 0xFFFF;
@@ -205,32 +320,54 @@ static SDL_bool AddDialogControl(WIN_DialogData *dialog, WORD type, DWORD style,
     if (!AddDialogData(dialog, &type, sizeof(type))) {
         return SDL_FALSE;
     }
-    if (!AddDialogString(dialog, caption)) {
-        return SDL_FALSE;
+    if (type == DLGITEMTYPEBUTTON || (type == DLGITEMTYPESTATIC && caption != NULL)) {
+        if (!AddDialogString(dialog, caption)) {
+            return SDL_FALSE;
+        }
+    } else {
+        if (!AddDialogData(dialog, &marker, sizeof(marker))) {
+            return SDL_FALSE;
+        }
+        if (!AddDialogData(dialog, &ordinal, sizeof(ordinal))) {
+            return SDL_FALSE;
+        }
     }
     if (!AddDialogData(dialog, &extraData, sizeof(extraData))) {
         return SDL_FALSE;
     }
+    if (type == DLGITEMTYPEBUTTON) {
+        dialog->numbuttons++;
+    }
     ++dialog->lpDialog->cDlgItems;
 
     return SDL_TRUE;
 }
 
-static SDL_bool AddDialogStatic(WIN_DialogData *dialog, int x, int y, int w, int h, const char *text)
+static SDL_bool AddDialogStaticText(WIN_DialogData *dialog, int x, int y, int w, int h, const char *text)
+{
+    DWORD style = WS_VISIBLE | WS_CHILD | SS_LEFT | SS_NOPREFIX | SS_EDITCONTROL | WS_GROUP;
+    return AddDialogControl(dialog, DLGITEMTYPESTATIC, style, 0, x, y, w, h, -1, text, 0);
+}
+
+static SDL_bool AddDialogStaticIcon(WIN_DialogData *dialog, int x, int y, int w, int h, Uint16 ordinal)
 {
-    DWORD style = WS_VISIBLE | WS_CHILD | SS_LEFT | SS_NOPREFIX | SS_EDITCONTROL;
-    return AddDialogControl(dialog, 0x0082, style, 0, x, y, w, h, -1, text);
+    DWORD style = WS_VISIBLE | WS_CHILD | SS_ICON | WS_GROUP;
+    return AddDialogControl(dialog, DLGITEMTYPESTATIC, style, 0, x, y, w, h, -2, NULL, ordinal);
 }
 
 static SDL_bool AddDialogButton(WIN_DialogData *dialog, int x, int y, int w, int h, const char *text, int id, SDL_bool isDefault)
 {
-    DWORD style = WS_VISIBLE | WS_CHILD;
+    DWORD style = WS_VISIBLE | WS_CHILD | WS_TABSTOP;
     if (isDefault) {
         style |= BS_DEFPUSHBUTTON;
     } else {
         style |= BS_PUSHBUTTON;
     }
-    return AddDialogControl(dialog, 0x0080, style, 0, x, y, w, h, id, text);
+    /* The first button marks the start of the group. */
+    if (dialog->numbuttons == 0) {
+        style |= WS_GROUP;
+    }
+    return AddDialogControl(dialog, DLGITEMTYPEBUTTON, style, 0, x, y, w, h, IDBUTTONINDEX0 + dialog->numbuttons, text, 0);
 }
 
 static void FreeDialogData(WIN_DialogData *dialog)
@@ -341,18 +478,87 @@ static WIN_DialogData *CreateDialogData(int w, int h, const char *caption)
     return dialog;
 }
 
+/* Escaping ampersands is necessary to disable mnemonics in dialog controls.
+ * The caller provides a char** for dst and a size_t* for dstlen where the
+ * address of the work buffer and its size will be stored. Their values must be
+ * NULL and 0 on the first call. src is the string to be escaped. On error, the
+ * function returns NULL and, on success, returns a pointer to the escaped
+ * sequence as a read-only string that is valid until the next call or until the
+ * work buffer is freed. Once all strings have been processed, it's the caller's
+ * responsibilty to free the work buffer with SDL_free, even on errors.
+ */
+static const char *EscapeAmpersands(char **dst, size_t *dstlen, const char *src)
+{
+    char *newdst;
+    size_t ampcount = 0;
+    size_t srclen = 0;
+
+    if (src == NULL) {
+        return NULL;
+    }
+
+    while (src[srclen]) {
+        if (src[srclen] == '&') {
+            ampcount++;
+        }
+        srclen++;
+    }
+    srclen++;
+
+    if (ampcount == 0) {
+        /* Nothing to do. */
+        return src;
+    }
+    if (SIZE_MAX - srclen < ampcount) {
+        return NULL;
+    }
+    if (*dst == NULL || *dstlen < srclen + ampcount) {
+        /* Allocating extra space in case the next strings are a bit longer. */
+        size_t extraspace = SIZE_MAX - (srclen + ampcount);
+        if (extraspace > 512) {
+            extraspace = 512;
+        }
+        *dstlen = srclen + ampcount + extraspace;
+        SDL_free(*dst);
+        *dst = NULL;
+        newdst = SDL_malloc(*dstlen);
+        if (newdst == NULL) {
+            return NULL;
+        }
+        *dst = newdst;
+    } else {
+        newdst = *dst;
+    }
+
+    /* The escape character is the ampersand itself. */
+    while (srclen--) {
+        if (*src == '&') {
+            *newdst++ = '&';
+        }
+        *newdst++ = *src++;
+    }
+
+    return *dst;
+}
+
 /* This function is called if a Task Dialog is unsupported. */
 static int
 WIN_ShowOldMessageBox(const SDL_MessageBoxData *messageboxdata, int *buttonid)
 {
     WIN_DialogData *dialog;
-    int i, x, y;
+    int i, x, y, retval;
     const SDL_MessageBoxButtonData *buttons = messageboxdata->buttons;
     HFONT DialogFont;
     SIZE Size;
     RECT TextSize;
     wchar_t* wmessage;
     TEXTMETRIC TM;
+    HDC FontDC;
+    INT_PTR result;
+    char *ampescape = NULL;
+    size_t ampescapesize = 0;
+    Uint16 defbuttoncount = 0;
+    Uint16 icon = 0;
 
     HWND ParentWindow = NULL;
 
@@ -360,7 +566,25 @@ WIN_ShowOldMessageBox(const SDL_MessageBoxData *messageboxdata, int *buttonid)
     const int ButtonHeight = 26;
     const int TextMargin = 16;
     const int ButtonMargin = 12;
+    const int IconWidth = GetSystemMetrics(SM_CXICON);
+    const int IconHeight = GetSystemMetrics(SM_CYICON);
+    const int IconMargin = 20;
+
+    if (messageboxdata->numbuttons > MAX_BUTTONS) {
+        return SDL_SetError("Number of butons exceeds limit of %d", MAX_BUTTONS);
+    }
 
+    switch (messageboxdata->flags) {
+    case SDL_MESSAGEBOX_ERROR:
+        icon = (Uint16)IDI_ERROR;
+        break;
+    case SDL_MESSAGEBOX_WARNING:
+        icon = (Uint16)IDI_WARNING;
+        break;
+    case SDL_MESSAGEBOX_INFORMATION:
+        icon = (Uint16)IDI_INFORMATION;
+        break;
+    }
 
     /* Jan 25th, 2013 - dant@fleetsa.com
      *
@@ -394,7 +618,7 @@ WIN_ShowOldMessageBox(const SDL_MessageBoxData *messageboxdata, int *buttonid)
      * In order to get text dimensions we need to have a DC with the desired font.
      * I'm assuming a dialog box in SDL is rare enough we can to the create.
      */
-    HDC FontDC = CreateCompatibleDC(0);
+    FontDC = CreateCompatibleDC(0);
 
     {
         /* Create a duplicate of the font used in system message boxes. */
@@ -429,11 +653,13 @@ WIN_ShowOldMessageBox(const SDL_MessageBoxData *messageboxdata, int *buttonid)
     /* Measure the *pixel* size of the string. */
     wmessage = WIN_UTF8ToString(messageboxdata->message);
     SDL_zero(TextSize);
-    DrawText(FontDC, wmessage, -1, &TextSize, DT_CALCRECT);
+    DrawText(FontDC, wmessage, -1, &TextSize, DT_CALCRECT | DT_LEFT | DT_NOPREFIX | DT_EDITCONTROL);
 
-    /* Add some padding for hangs, etc. */
-    TextSize.right += 2;
-    TextSize.bottom += 2;
+    /* Add margins and some padding for hangs, etc. */
+    TextSize.left += TextMargin;
+    TextSize.right += TextMargin + 2;
+    TextSize.top += TextMargin;
+    TextSize.bottom += TextMargin + 2;
 
     /* Done with the DC, and the string */
     DeleteDC(FontDC);
@@ -445,10 +671,22 @@ WIN_ShowOldMessageBox(const SDL_MessageBoxData *messageboxdata, int *buttonid)
     Size.cx += TextMargin * 2;
     Size.cy += TextMargin * 2;
 
+    /* Make dialog wider and shift text over for the icon. */
+    if (icon) {
+        Size.cx += IconMargin + IconWidth;
+        TextSize.left += IconMargin + IconWidth;
+        TextSize.right += IconMargin + IconWidth;
+    }
+
     /* Ensure the size is wide enough for all of the buttons. */
     if (Size.cx < messageboxdata->numbuttons * (ButtonWidth + ButtonMargin) + ButtonMargin)
         Size.cx = messageboxdata->numbuttons * (ButtonWidth + ButtonMargin) + ButtonMargin;
 
+    /* Reset the height to the icon size if it is actually bigger than the text. */
+    if (icon && Size.cy < IconMargin * 2 + IconHeight) {
+        Size.cy = IconMargin * 2 + IconHeight;
+    }
+
     /* Add vertical space for the buttons and border. */
     Size.cy += ButtonHeight + TextMargin;
 
@@ -457,7 +695,12 @@ WIN_ShowOldMessageBox(const SDL_MessageBoxData *messageboxdata, int *buttonid)
         return -1;
     }
 
-    if (!AddDialogStatic(dialog, TextMargin, TextMargin, TextSize.right - TextSize.left, TextSize.bottom - TextSize.top, messageboxdata->message)) {
+    if (icon && ! AddDialogStaticIcon(dialog, IconMargin, IconMargin, IconWidth, IconHeight, icon)) {
+        FreeDialogData(dialog);
+        return -1;
+    }
+
+    if (!AddDialogStaticText(dialog, TextSize.left, TextSize.top, TextSize.right - TextSize.left, TextSize.bottom - TextSize.top, messageboxdata->message)) {
         FreeDialogData(dialog);
         return -1;
     }
@@ -466,19 +709,25 @@ WIN_ShowOldMessageBox(const SDL_MessageBoxData *messageboxdata, int *buttonid)
     x = Size.cx - (ButtonWidth + ButtonMargin) * messageboxdata->numbuttons;
     y = Size.cy - ButtonHeight - ButtonMargin;
     for (i = messageboxdata->numbuttons - 1; i >= 0; --i) {
-        SDL_bool isDefault;
+        SDL_bool isdefault = SDL_FALSE;
+        const char *buttontext;
 
         if (buttons[i].flags & SDL_MESSAGEBOX_BUTTON_RETURNKEY_DEFAULT) {
-            isDefault = SDL_TRUE;
-        } else {
-            isDefault = SDL_FALSE;
+            defbuttoncount++;
+            if (defbuttoncount == 1) {
+                isdefault = SDL_TRUE;
+            }
         }
-        if (!AddDialogButton(dialog, x, y, ButtonWidth, ButtonHeight, buttons[i].text, buttons[i].buttonid, isDefault)) {
+
+        buttontext = EscapeAmpersands(&ampescape, &ampescapesize, buttons[i].text);
+        if (buttontext == NULL || !AddDialogButton(dialog, x, y, ButtonWidth, ButtonHeight, buttontext, buttons[i].buttonid, isdefault)) {
             FreeDialogData(dialog);
+            SDL_free(ampescape);
             return -1;
         }
         x += ButtonWidth + ButtonMargin;
     }
+    SDL_free(ampescape);
 
     /* If we have a parent window, get the Instance and HWND for them
      * so that our little dialog gets exclusive focus at all times. */
@@ -486,10 +735,32 @@ WIN_ShowOldMessageBox(const SDL_MessageBoxData *messageboxdata, int *buttonid)
         ParentWindow = ((SDL_WindowData*)messageboxdata->window->driverdata)->hwnd;
     }
 
-    *buttonid = (int)DialogBoxIndirect(NULL, (DLGTEMPLATE*)dialog->lpDialog, ParentWindow, (DLGPROC)MessageBoxDialogProc);
+    result = DialogBoxIndirectParam(NULL, (DLGTEMPLATE*)dialog->lpDialog, ParentWindow, (DLGPROC)MessageBoxDialogProc, (LPARAM)messageboxdata);
+    if (result >= IDBUTTONINDEX0 && result - IDBUTTONINDEX0 < messageboxdata->numbuttons) {
+        *buttonid = messageboxdata->buttons[(messageboxdata->numbuttons - 1) - (result - IDBUTTONINDEX0)].buttonid;
+        retval = 0;
+    } else if (result == IDCLOSED) {
+        /* Dialog window closed by user or system. */
+        /* This could use a special return code. */
+        retval = 0;
+        *buttonid = -1;
+    } else {
+        if (result == 0) {
+            SDL_SetError("Invalid parent window handle");
+        } else if (result == -1) {
+            SDL_SetError("The message box encountered an error.");
+        } else if (result == IDINVALPTRINIT || result == IDINVALPTRSETFOCUS || result == IDINVALPTRCOMMAND) {
+            SDL_SetError("Invalid message box pointer in dialog procedure");
+        } else if (result == IDINVALPTRDLGITEM) {
+            SDL_SetError("Couldn't find dialog control of the default enter-key button");
+        } else {
+            SDL_SetError("An unknown error occured");
+        }
+        retval = -1;
+    }
 
     FreeDialogData(dialog);
-    return 0;
+    return retval;
 }
 
 /* TaskDialogIndirect procedure
@@ -509,16 +780,22 @@ WIN_ShowMessageBox(const SDL_MessageBoxData *messageboxdata, int *buttonid)
     HMODULE hComctl32;
     TASKDIALOGINDIRECTPROC pfnTaskDialogIndirect;
     HRESULT hr;
+    char *ampescape = NULL;
+    size_t ampescapesize = 0;
     int nButton;
     int nCancelButton;
     int i;
 
+    if (SIZE_MAX / sizeof(TASKDIALOG_BUTTON) < messageboxdata->numbuttons) {
+        return SDL_OutOfMemory();
+    }
+
     /* If we cannot load comctl32.dll use the old messagebox! */
     hComctl32 = LoadLibrary(TEXT("Comctl32.dll"));
     if (hComctl32 == NULL) {
-        return WIN_ShowOldMessageBox(messageboxdata,buttonid);
+        return WIN_ShowOldMessageBox(messageboxdata, buttonid);
     }
-    
+
     /* If TaskDialogIndirect doesn't exist use the old messagebox!
        This will fail prior to Windows Vista.
        The manifest file in the application may require targeting version 6 of comctl32.dll, even
@@ -563,6 +840,7 @@ WIN_ShowMessageBox(const SDL_MessageBoxData *messageboxdata, int *buttonid)
     nCancelButton = 0;
     for (i = 0; i < messageboxdata->numbuttons; i++)
     {
+        const char *buttontext;
         pButton = &pButtons[messageboxdata->numbuttons-1-i];
         if (messageboxdata->buttons[i].flags & SDL_MESSAGEBOX_BUTTON_ESCAPEKEY_DEFAULT) {
             nCancelButton = messageboxdata->buttons[i].buttonid;
@@ -573,7 +851,20 @@ WIN_ShowMessageBox(const SDL_MessageBoxData *messageboxdata, int *buttonid)
                 pButton->nButtonID++;
             }
         }
-        pButton->pszButtonText = WIN_UTF8ToString(messageboxdata->buttons[i].text);
+        buttontext = EscapeAmpersands(&ampescape, &ampescapesize, messageboxdata->buttons[i].text);
+        if (buttontext == NULL) {
+            int j;
+            FreeLibrary(hComctl32);
+            SDL_free(ampescape);
+            SDL_free(wmessage);
+            SDL_free(wtitle);
+            for (j = 0; j < i; j++) {
+                SDL_free((wchar_t *) pButtons[j].pszButtonText);
+            }
+            SDL_free(pButtons);
+            return -1;
+        }
+        pButton->pszButtonText = WIN_UTF8ToString(buttontext);
         if (messageboxdata->buttons[i].flags & SDL_MESSAGEBOX_BUTTON_RETURNKEY_DEFAULT) {
             TaskConfig.nDefaultButton = pButton->nButtonID;
         }
@@ -585,6 +876,7 @@ WIN_ShowMessageBox(const SDL_MessageBoxData *messageboxdata, int *buttonid)
 
     /* Free everything */
     FreeLibrary(hComctl32);
+    SDL_free(ampescape);
     SDL_free(wmessage);
     SDL_free(wtitle);
     for (i = 0; i < messageboxdata->numbuttons; i++) {