Using Messages and Message Queues

The following code examples demonstrate how to perform the following tasks associated with Windows messages and message queues.

Creating a Message Loop

The system does not automatically create a message queue for each thread. Instead, the system creates a message queue only for threads that perform operations which require a message queue. If the thread creates one or more windows, a message loop must be provided; this message loop retrieves messages from the thread’s message queue and dispatches them to the appropriate window procedures.

Because the system directs messages to individual windows in an application, a thread must create at least one window before starting its message loop. Most applications contain a single thread that creates windows. A typical application registers the window class for its main window, creates and shows the main window, and then starts its message loop — all in the WinMain function.

You create a message loop by using the GetMessage and DispatchMessage functions. If your application must obtain character input from the user, include the TranslateMessage function in the loop. TranslateMessage translates virtual-key messages into character messages. The following example shows the message loop in the WinMain function of a simple Windows-based application.

The following example shows a message loop for a thread that uses accelerators and displays a modeless dialog box. When TranslateAccelerator or IsDialogMessage returns TRUE (indicating that the message has been processed), TranslateMessage and DispatchMessage are not called. The reason for this is that TranslateAccelerator and IsDialogMessage perform all necessary translating and dispatching of messages.

Examining a Message Queue

Occasionally, an application needs to examine the contents of a thread’s message queue from outside the thread’s message loop. For example, if an application’s window procedure performs a lengthy drawing operation, you may want the user to be able to interrupt the operation. Unless your application periodically examines the message queue during the operation for mouse and keyboard messages, it will not respond to user input until after the operation has completed. The reason for this is that the DispatchMessage function in the thread’s message loop does not return until the window procedure finishes processing a message.

You can use the PeekMessage function to examine a message queue during a lengthy operation. PeekMessage is similar to the GetMessage function; both check a message queue for a message that matches the filter criteria and then copy the message to an MSG structure. The main difference between the two functions is that GetMessage does not return until a message matching the filter criteria is placed in the queue, whereas PeekMessage returns immediately regardless of whether a message is in the queue.

The following example shows how to use PeekMessage to examine a message queue for mouse clicks and keyboard input during a lengthy operation.

Other functions, including GetQueueStatus and GetInputState, also allow you to examine the contents of a thread’s message queue. GetQueueStatus returns an array of flags that indicates the types of messages in the queue; using it is the fastest way to discover whether the queue contains any messages. GetInputState returns TRUE if the queue contains mouse or keyboard messages. Both of these functions can be used to determine whether the queue contains messages that need to be processed.

Posting a Message

You can post a message to a message queue by using the PostMessage function. PostMessage places a message at the end of a thread’s message queue and returns immediately, without waiting for the thread to process the message. The function’s parameters include a window handle, a message identifier, and two message parameters. The system copies these parameters to an MSG structure, fills the time and pt members of the structure, and places the structure in the message queue.

The system uses the window handle passed with the PostMessage function to determine which thread message queue should receive the message. If the handle is HWND_TOPMOST, the system posts the message to the thread message queues of all top-level windows.

You can use the PostThreadMessage function to post a message to a specific thread message queue. PostThreadMessage is similar to PostMessage, except the first parameter is a thread identifier rather than a window handle. You can retrieve the thread identifier by calling the GetCurrentThreadId function.

Use the PostQuitMessage function to exit a message loop. PostQuitMessage posts the WM_QUIT message to the currently executing thread. The thread’s message loop terminates and returns control to the system when it encounters the WM_QUIT message. An application usually calls PostQuitMessage in response to the WM_DESTROY message, as shown in the following example.

Sending a Message

The SendMessage function is used to send a message directly to a window procedure. SendMessage calls a window procedure and waits for that procedure to process the message and return a result.

A message can be sent to any window in the system; all that is required is a window handle. The system uses the handle to determine which window procedure should receive the message.

Before processing a message that may have been sent from another thread, a window procedure should first call the InSendMessage function. If this function returns TRUE, the window procedure should call ReplyMessage before any function that causes the thread to yield control, as shown in the following example.

A number of messages can be sent to controls in a dialog box. These control messages set the appearance, behavior, and content of controls or retrieve information about controls. For example, the CB_ADDSTRING message can add a string to a combo box, and the BM_SETCHECK message can set the check state of a check box or radio button.

Use the SendDlgItemMessage function to send a message to a control, specifying the identifier of the control and the handle of the dialog box window that contains the control. The following example, taken from a dialog box procedure, copies a string from a combo box’s edit control into its list box. The example uses SendDlgItemMessage to send a CB_ADDSTRING message to the combo box.

Messaging (Windows Configuration Designer reference)

Use for settings related to Messaging and Commercial Mobile Alert System (CMAS).

These settings are intended to be used only by manufacturers, mobile operators, and solution providers when configuring devices, and are not intended for use by administrators in the enterprise.

CMAS is now known as Wireless Emergency Alerts (WEA).

Applies to

Setting	Desktop editions	Mobile editions	Surface Hub	HoloLens	IoT Core
All settings	X

GlobalSettings

DisplayCmasLifo

Use this setting to change the order in which CMAS alert messages are displayed, from the default first in/first out (FIFO) message order to last in/first out (LIFO) message order.

If the phone receives at least one CMAS alert message which has not been acknowledged by the user, and another CMAS alert message arrives on the phone, partners can configure the order in which the newly received alert messages are displayed on the phone regardless of the service category of the alert. Users will not be able to change the message order once it has been set.

If partners do not specify a value for this customization, the default FIFO display order is used. Users will be able to acknowledge the messages in the reverse order they were received.

When configured as True, you set a LIFO message order. When configured as False, you set a FIFO message order.

EnableCustomLineSetupDialog

Enable this setting to allow custom line setup dialogs in the Messaging app.

ExtractPhoneNumbersInStrings»

Set as True to tag any 5-or-more digit number as a tappable phone number.

ShowSendingStatus

This setting is removed in Windows 10, version 1709.

Set ShowSendingStatus to True to display the sending status for SMS/MMS messages.

VoicemailIntercept

Partners can define a filter that intercepts an incoming SMS message and triggers visual voicemail synchronization. The filtered message does not appear in the user’s conversation list.

A visual voicemail sync is triggered by an incoming SMS message if the following conditions are met:

The message sender value starts with the string specified in the SyncSender setting. The length of the specified values must be greater than 3 characters but less than 75 characters.

The body of the message starts with the string specified in the SyncPrefix setting. The length of the specified values must be greater than 3 characters but less than 75 characters.

Visual voicemail is configured and enabled. For more information, see Visual voicemail.

These settings are atomic, so both SyncSender and SyncPrefix must be set.

The SyncSender and SyncPrefix values vary for each mobile operator, so you must work with your mobile operators to obtain the correct or required values.

Setting	Description
SyncPrefix	Specify a value for SyncPrefix that is greater than 3 characters but less than 75 characters in length. For networks that support it, this value can be the keyword for the SMS notification.
SyncSender	Specify a value for SyncSender that is greater than 3 characters but less than 75 characters in length. For networks that support it, this value can be a short code of the mailbox server that sends a standard SMS notification.

PerSimSettings

Use to configure settings for each subscriber identification module (SIM) card. Enter the Integrated Circuit Card Identifier (ICCID) for the SIM card, click Add, and then configure the following settings.

AllowMmsIfDataIsOff

Setting	Description
AllowMmsIfDataIsOff	True allows MMS if data is off
AllowMmsIfDataIsOffSupported	True shows the toggle for allowing MMS if data is turned off
AllowMmsIfDataIsOffWhileRoaming	True allows MMS if data is off while roaming

AllowSelectAllContacts

This setting is removed in Windows 10, version 1709, and later.

Set to True to show the select all contacts/unselect all menu option to allow users to easily select multiple recipients for an SMS or MMS message. This menu option provides users with an easier way to add multiple recipients and may also meet a mandatory requirement for some mobile operator networks.

Windows 10 Mobile supports the following select multiple recipients features:

• A multi-select chooser, which enables users to choose multiple contacts.
• A select all contacts/unselect all menu option, which enables users to select or unselect all their contacts. This option is not shown by default and must be enabled by the OEM.

AllowSendingDeliveryReport

Specify whether the phone automatically sends a receipt acknowledgment for MMS messages. Partners can specify whether the phone automatically sends a receipt acknowledgment for MMS messages when they arrive, and they can determine whether users can control the receipt acknowledgments by using the Send MMS acknowledgment toggle in Messaging > settings. By default, this user setting is visible and turned on.

Setting	Description
AllowSendingDeliveryReport	True sets the Send MMS acknowledgment toggle to On
AllowSendingDeliveryReportIsSupported	True shows the Send MMS acknowledgment toggle, and False hides the toggle

AutomaticallyDownload

Specify whether MMS messages are automatically downloaded.

Setting	Description
AutomaticallyDownload	True sets the Automatically download MMS toggle to On
ShowAutomaticallyDownloadMMSToggle	True shows the Automatically download MMS toggle, and False hides the toggle

DefaultContentLocationUrl

This setting is removed in Windows 10, version 1709.

For networks that require it, you can specify the default GET path within the MMSC to use when the GET URL is missing from the WAP push MMS notification.

Set DefaultContentLocationUrl to specify the default GET path within the MMSC.

ErrorCodeEnabled

This setting is removed in Windows 10, version 1709.

You can choose to display additional content in the conversation view when an SMS or MMS message fails to send. This content includes a specific error code in decimal format that the user can report to technical support. Common errors also include a friendly string to help the user self-diagnose and fix the problem.

Set to True to display the error message with an explanation of the problem and the decimal-format error codes. When set to False, the full error message is not displayed.

EmergencyAlertOptions

Configure settings for CMAS alerts.

Setting	Description
CmasAMBERAlertEnabled	True enables the device to receive AMBER alerts
CmasExtremeAlertEnabled	True enables the device to receive extreme alerts
CmasSevereAlertEnabled	True enables the device to receive severe alerts
EmOperatorEnabled	Select which Emergency Alerts Settings page is displayed from dropdown menu
EtwsSoundEnabled	Set to True to play Earthquake & Tsunami Warning System (ETWS) sound during alert.
SevereAlertDependentOnExtremeAlert	When set as True, the CMAS-Extreme alert option must be on to modify CMAS-Severe alert option

General

Setting	Description
AllowSelectAllContacts	Set to True to show the select all contacts/unselect all menu option to allow users to easily select multiple recipients for an SMS or MMS message. This menu option provides users with an easier way to add multiple recipients and may also meet a mandatory requirement for some mobile operator networks. Windows 10 Mobile supports the following select multiple recipients features: — A multi-select chooser, which enables users to choose multiple contacts. — A select all contacts/unselect all menu option, which enables users to select or unselect all their contacts. This option is not shown by default and must be enabled by the OEM.
AllowSMStoSMTPAddress	Allow SMS to SMTP address.
AssistedDialingMcc	By setting AssistedDialingMcc and AssistedDialingMnc, international assisted dialing will be enabled for SMS if the user setting for international assisted dialing is enabled. Enter the Mobile Country Code (MCC) to use for sending SMS.
AssistedDialingMnc	By setting AssistedDialingMcc and AssistedDialingMnc, international assisted dialing will be enabled for SMS if the user setting for international assisted dialing is enabled. Enter the Mobile Network Code (MNC) to use for sending SMS.
AssistedDialingPlusCodeSupportOverride	For devices that support IMS over SMS, you can override support for the assisted dialing plus (+) code for SMS by setting AssistedDialingPlusCodeSupportOverride. If enabled, the OS will not convert the plus (+) code to the proper assisted number when the user turns on the dialing assist option.
AutoRetryDownload	You can configure the messaging app to automatically retry downloading an MMS message if the initial download attempt fails. When this customization is enabled, the download is retried 3 times at 20-, 40-, and 60-second intervals.
BroadcastChannels	You can specify one or more ports from which the device will accept cellular broadcast messages. Set the BroadcastChannels value to the port number(s) that can accept cellular broadcast messages. If you specify the same port that Windows 10 Mobile already recognizes as an Emergency Alert port (a CMAS or ETWS port number) and a cell broadcast message is received on that port, the user will only receive the message once. The message that is received will be displayed as an Emergency Alert message.
ConvertLongSMStoMMS	For networks that do support MMS and do not support segmentation of SMS messages, you can specify an automatic switch from SMS to MMS for long messages.
DefaultContentLocationUrl	For networks that require it, you can specify the default GET path within the MMSC to use when the GET URL is missing from the WAP push MMS notification. Set DefaultContentLocationUrl to specify the default GET path within the MMSC.
EarthquakeMessageString	To override the Primary Earthquake default message, specify the EarthquakeMessageString setting value. This string will be used regardless of what language is set on the device.
EarthquakeTsunamiMessageString	To override the Primary Tsunami and Earthquake default message, specify the EarthquakeTsunamiMessageString setting value. This string will be used regardless of what language is set on the device.
ErrorCodeEnabled	You can choose to display additional content in the conversation view when an SMS or MMS message fails to send. This content includes a specific error code in decimal format that the user can report to technical support. Common errors also include a friendly string to help the user self-diagnose and fix the problem. Set to True to display the error message with an explanation of the problem and the decimal-format error codes. When set to False, the full error message is not displayed.
EtwsSoundFileName	Set the value to the name of a sound file.
HideMediumSIPopups	By default, when a service indication message is received with a signal-medium or signal-high setting, the phone interrupts and shows the user prompt for these messages. However, you can hide the user prompts for signal-medium messages.
ImsiAuthenticationToken	Configure whether MMS messages include the IMSI in the GET and POST header. Set ImsiAuthenticationToken to the token used as the header for authentication. The string value should match the IMSI provided by the UICC.
LimitRecipients	Set the maximum number of recipients to which a single SMS or MMS message can be sent. Enter a number between 1 and 500 to limit the maximum number of recipients.
MaxRetryCount	You can specify the number of times that the phone can retry sending the failed MMS message and photo before the user receives a notification that the photo could not be sent. Specify MaxRetryCount to specify the number of times the MMS transport will attempt resending the MMS message. This value has a maximum limit of 3.
MMSLimitAttachments	You can specify the maximum number of attachments for MMS messages, from 1 to 20. The default is 5.
NIInfoEnabled	NIInfoEnabled
ProxyAuthorizationToken	See Proxy authorization for MMS.
RetrySize	For MMS messages that have photo attachments and that fail to send, you can choose to automatically resize the photo and attempt to resend the message. Specify the maximum size to use to resize the photo in KB. Minimum is 0xA (10 KB).
SetCacheControlNoTransform	When set, proxies and transcoders are instructed not to change the HTTP header and the content should not be modified. A value of 1 or 0x1 adds support for the HTTP header Cache-Control No-Transform directive. When the SetCacheControlNoTransform«Value is set to 0 or 0x0 or when the setting is not set, the default HTTP header Cache-Control No-Cache directive is used.
ShowRequiredMonthlyTest	True enables devices to receive CMAS Required Monthly Test (RMT) messages and have these show up on the device. False disables devices from receiving CMAS RMT messages.
SIProtocols	Additional supported service indication protocol name.
SmscPanelDisabled	True disables the short message service center (SMSC) panel.
SMStoSMTPShortCode	Use to configure SMS messages to be sent to email addresses and phone numbers. 0 disables sending SMS messages to SMTP addresses. 1 enables sending SMS messages to SMTP addresses.
TargetVideoFormat	You can specify the transcoding to use for video files sent as attachments in MMS messages. Set TargetVideoFormat to one of the following values to configure the default transcoding for video files sent as attachments in MMS messages: — 0 or 0x0 Sets the transcoding to H.264 + AAC + MP4. This is the default set by the OS. — 1 or 0x1 Sets the transcoding to H.264 + AAC + 3GP. — 2 or 0x2 Sets the transcoding to H.263 + AMR.NB + 3GP. — 3 or 0x3 Sets the transcoding to MPEG4 + AMR.NB + 3GP.
TsunamiMessageString	To override the Primary Tsunami default message, specify the TsunamiMessageString setting value. This string will be used regardless of what language is set on the device.
UAProf	You can specify a user agent profile to use on the phone for MMS messages. The user agent profile XML file details a phone’s hardware specifications and media capabilities so that an MMS application server (MMSC) can return supported optimized media content to the phone. The user agent profile XML file is generally stored on the MMSC. There are two ways to correlate a user agent profile with a given phone: — You can take the user agent string of the phone that is sent with MMS requests and use it as a hash to map to the user agent profile on the MMSC. The user agent string cannot be modified. — Alternatively, you can directly set the URI of the user agent profile on the phone. Set UAProf to the full URI of your user agent profile file. Optionally, you can also specify the custom user agent property name for MMS that is sent in the header by setting UAProfToken to either x-wap-profile or profile .
UAProfToken	You can specify a user agent profile to use on the phone for MMS messages. The user agent profile XML file details a phone’s hardware specifications and media capabilities so that an MMS application server (MMSC) can return supported optimized media content to the phone. The user agent profile XML file is generally stored on the MMSC.
UseDefaultAddress	By default, the MMS transport sends an acknowledgement to the provisioned MMS application server (MMSC). However, on some networks, the correct server to use is sent as a URL in the MMS message. In that case, a registry key must be set, or else the acknowledgement will not be received and the server will continue to send duplicate messages. True enables some networks to correctly acknowledge MMS messages. False disables the feature.
UseInsertAddressToken	Use insert address token or local raw address.
UserAgentString	Set UserAgentString to the new user agent string for MMS in its entirely. By default, this string has the format WindowsPhoneMMS/MicrosoftMMSVersionNumber WindowsPhoneOS/OSVersion-buildNumber OEM-deviceName, in which the italicized text is replaced with the appropriate values for the phone.
UseUTF8ForUnspecifiedCharset	Some incoming MMS messages may not specify a character encoding. To properly decode MMS messages that do not specify a character encoding, you can set UTF-8 to decode the message.
WapPushTechnology	For networks that require non-standard handling of single-segment incoming MMS WAP Push notifications, you can specify that MMS messages may have some of their content truncated and that they may require special handling to reconstruct truncated field values. 1 or 0x1 enables MMS messages to have some of their content truncated. 0 or 0x0 disables MMS messages from being truncated

ImsiAuthenticationToken

This setting is removed in Windows 10, version 1709.

Configure whether MMS messages include the IMSI in the GET and POST header.

Set ImsiAuthenticationToken to the token used as the header for authentication. The string value should match the IMSI provided by the UICC.

LatAlertOptions

Enable LatLocalAlertEnabled to enable support for LAT-Alert Local Alerts for devices sold in Chile. For more information, see Emergency notifications.

MaxRetryCount

This setting is removed in Windows 10, version 1709.

You can specify the number of times that the phone can retry sending the failed MMS message and photo before the user receives a notification that the photo could not be sent.

Specify MaxRetryCount to specify the number of times the MMS transport will attempt resending the MMS message. This value has a maximum limit of 3.

MMSGroupText

Set options for group messages sent to multiple people.

Setting	Description
MMSGroupText	True enables group messages to multiple people sent as MMS.
ShowMMSGroupTextUI	True shows the toggle for group text in messaging settings.
ShowMmsGroupTextWarning	True shows the warning that alerts users of possible additional charges before sending a group text as MMS.

NIAlertOptions

Enable NI2AlertEnabled to enable support for the Netherlands Announcements for devices sold in the Netherlands. For more information, see Emergency notifications.

RcsOptions

Set options for Rich Communications Services (RCS).

Setting	Description
RcsAllowLeaveClosedGroupChats	Whether or not to allow users to leave closed group chats.
RcsEnabled	Toggle to enable/disable RCS service. Set to True to enable.
RcsFileTransferAutoAccept	Set to True to auto-accept RCS incoming file transfer if the file size is less than warning file size.
RcsFiletransferAutoAcceptWhileRoaming	Auto-accept RCS incoming file transfer when the file size is less than the warning file size while roaming.
RcsGroupChatCreationMode	The mode used to create new RCS group chats.
RcsGroupChatCreationgThreadingMode	The mode used to thread newly created RCS group chats.
RcsSendReadReceipt	Set to True to send read receipt to the sender when a message is read.
RcsTimeWindowsAfterSelfLeave	After RCS receives a self-left message, it will ignore messages during this time (in milliseconds), except self-join.
ShowRcsEnabled	Set to True to show the toggle for RCS activation.

RequestDeliveryReport

Set options related to MMS message notifications. You can specify whether users receive notification that MMS messages could not be delivered, and determine whether users can control this by using the MMS delivery confirmation toggle in Messaging > settings. By default, this user setting is visible but turned off.

Setting	Description
RequestDeliveryReport	Set to True to set the default value to on.
RequestDeliveryReportIsSupported	True shows the toggle for MMS delivery confirmation, and False hides the toggle.

SMSDeliveryNotify

Setting	Description
DeliveryNotifySupported	Set to True to enable SMS delivery confirmation.
SMSDeliveryNotify	Set to True to toggle SMS delivery confirmation.

TargetVideoFormat

This setting is removed in Windows 10, version 1709.

You can specify the transcoding to use for video files sent as attachments in MMS messages.

Set TargetVideoFormat to one of the following values to configure the default transcoding for video files sent as attachments in MMS messages:

Value	Description
0 or 0x0	Sets the transcoding to H.264 + AAC + MP4. This is the default set by the OS.
1 or 0x1	Sets the transcoding to H.264 + AAC + 3GP.
2 or 0x2	Sets the transcoding to H.263 + AMR.NB + 3GP.
3 or 0x3	Sets the transcoding to MPEG4 + AMR.NB + 3GP.

TaiwanAlertOptions

Set options for Taiwan Emergency Alerts system. For more information, see Emergency notifications.

Setting	Description
TaiwanAlertEnabled	Receive Taiwan alerts.
TaiwanEmergencyAlertEnabled	Receive Taiwan emergency alerts.
TaiwanPresidentialAlertEnabled	Receive alerts from the Leader of the Taiwan Area.
TaiwanRequiredMonthlytestEnabled	Receive Taiwan Required Monthly Test alerts.

UAProf

This setting is removed in Windows 10, version 1709.

You can specify a user agent profile to use on the phone for MMS messages. The user agent profile XML file details a phone’s hardware specifications and media capabilities so that an MMS application server (MMSC) can return supported optimized media content to the phone. The user agent profile XML file is generally stored on the MMSC.

There are two ways to correlate a user agent profile with a given phone:

• You can take the user agent string of the phone that is sent with MMS requests and use it as a hash to map to the user agent profile on the MMSC. The user agent string cannot be modified.
• Alternatively, you can directly set the URI of the user agent profile on the phone.

Set UAProf to the full URI of your user agent profile file. Optionally, you can also specify the custom user agent property name for MMS that is sent in the header by setting UAProfToken to either x-wap-profile or profile .

UAProfToken

This setting is removed in Windows 10, version 1709.

You can specify a user agent profile to use on the phone for MMS messages. The user agent profile XML file details a phone’s hardware specifications and media capabilities so that an MMS application server (MMSC) can return supported optimized media content to the phone. The user agent profile XML file is generally stored on the MMSC.

Optionally, in addition to specifying UAProf, you can also specify the custom user agent property name for MMS that is sent in the header by setting UAProfToken to either x-wap-profile or profile .

UserAgentString

This setting is removed in Windows 10, version 1709.

Set UserAgentString to the new user agent string for MMS in its entirely.

By default, this string has the format WindowsPhoneMMS/MicrosoftMMSVersionNumber WindowsPhoneOS/OSVersion-buildNumber OEM-deviceName, in which the italicized text is replaced with the appropriate values for the phone.

Setting	Description
ADDR	Specify the absolute MMSC URL. The possible values to configure the ADDR parameter are: — A Uniform Resource Identifier (URI) — An IPv4 address represented in decimal format with dots as delimiters — A fully qualified Internet domain name
APPID	Set to w4 .
MS	(optional) Specify the maximum size of MMS, in KB. If the value is not a number, or is less than or equal to 10, it will be ignored and outgoing MMS will not be resized.
NAME	(optional) Enter user–readable application identity. This parameter is also used to define part of the registry path for the APPLICATION parameters. The possible values to configure the NAME parameter are: — Character string containing the name — no value specified If no value is specified, the registry location will default to . If NAME is greater than 40 characters, it will be truncated to 40 characters.
TONAPID	Specify the network access point identification name (NAPID) defined in the provisioning file. This parameter takes a string value. It is only possible to refer to network access points defined within the same provisioning file (except if the INTERNET attribute is set in the NAPDEF characteristic). For more information about the NAPDEF characteristic, see NAPDEF configuration service provider.
TOPROXY	Specify one logical proxy with a matching PROXY-ID. It is only possible to refer to proxies defined within the same provisioning file. Only one proxy can be listed. The TO-PROXY value must be set to the value of the PROXY ID in PXLOGICAL that defines the MMS specific-proxy.

WapPushTechnology

These settings are removed in Windows 10, version 1709.

For networks that require non-standard handling of single-segment incoming MMS WAP Push notifications, you can specify that MMS messages may have some of their content truncated and that they may require special handling to reconstruct truncated field values.