Help Explorer Viewer can be integrated into any Windows or Linux application no matter what language and environment the application was created in. Integration means that your applications will call Help Explorer Viewer as a viewer for the help files that document the applications' functionality.

To integrate Help Explorer Viewer into your application, use the contents of the Help Explorer Viewer integration package, which includes all necessary modules and permissions. After installation, uncompress its contents to an appropriate directory. The libraries libhelpexplapi.so (in the Linux package) or helpexplapi.dll (in the Windows package) implement the interface between your applications and the help system provided by Help Explorer Viewer. The Help Explorer Viewer API is fully compatible with the WinHelp API.

Help Explorer Viewer API

The InvokeHelp function starts Help Explorer Viewer and passes it additional data indicating the nature of the help requested by the application. InvokeHelp closely resembles Windows' WinHelp function:

BOOL InvokeHelp(
    uint hWnd,
    LPCTSTR lpszHelpFile,
    uint fuCommand,
    void* dwData
);

Parameter	Description
hWnd	Handle of the window requesting Help. The InvokeHelp function uses this handle to keep track of which programs have requested Help. If fuCommand specifies HELP_CONTEXTMENU or HELP_WM_HELP, hWnd identifies the control requesting Help.
lpszHelpFile	Address of a null-terminated string containing the path, if necessary, and the name of the Help file that HelpExplorer is to display. The filename may be followed by an angle bracket (>) and the name of a secondary window if the topic is to be displayed in a secondary window rather than in the primary window.
fuCommand	Type of help requested. For a list of possible values and how they affect the value to place in the dwData parameter, see below.
dwData	Additional data. The value used depends on the value of the fuCommand parameter. For a list of possible values, see below.

Return Value

If successful, the return value is TRUE. Otherwise, it is FALSE.

Comments

lpszHelpFile parameter specifies the name and, where required, the directory path of the Help file to display. Before closing the window that requested Help, the application should call InvokeHelp with the fuCommand parameter set to HELP_QUIT. Until all applications have done this, Help Explorer Viewer process remains in the system.

Note: calling InvokeHelp with the HELP_QUIT command is not necessary if you used the HELP_CONTEXTPOPUP command to start Help.

The following table shows the possible values for the fuCommand parameter and the corresponding formats of the dwData parameter:

fuCommand	Action	dwData
HELP_COMMAND	Runs a Help macro or macro string.	Address of a string that specifies the name of the Help macro(s) to run. If the string specifies multiple macro names, the names must be separated by colons or semicolons. The short form of the macro name is preferred.
HELP_CONTENTS	Displays the topic specified by the Contents option in the [OPTIONS] section of the .HPJ file. This command is for backward compatibility. New programs should provide a .CNT file and use the HELP_FINDER command.	Ignored.
HELP_CONTEXT	Displays the topic identified by the specified context identifier defined in the [MAP] section of the .HPJ file.	Unsigned long integer containing the context identifier for the topic.
HELP_CONTEXTMENU	Displays the Help menu for the selected window, and then displays (in a popup window) the topic for the selected control.	Address of an array of double word pairs. The first double word in each pair is a control identifier, and the second is a context number for a topic.
HELP_CONTEXTPOPUP	Displays, in a popup window, the topic identified by the specified context identifier defined in the [MAP] section of the .HPJ file.	Unsigned long integer containing the context identifier for a topic.
HELP_FINDER	Displays the Help Topics dialog box.	Ignored.
HELP_FORCEFILE	Ensures that Help Explorer Viewer is displaying the correct Help file. If the incorrect Help file is being displayed, HelpExplorer opens the correct one. Otherwise, there is no action.	Ignored.
HELP_HELPONHELP	Displays Help on how to use Help Explorer Viewer, if the HelpExpl.HLP file is available.	Ignored.
HELP_INDEX	Displays the topic specified by the CONTENTS option in the [OPTIONS] section of the .HPJ file. This command is for backward compatibility. New programs should provide a .CNT file and use the HELP_FINDER command.	Ignored.
HELP_KEY	Displays the topic in the keyword table that matches the specified keyword, if there is an exact match. If there is more than one match, this command displays the Topics Found list box.	Address of a keyword string. Multiple keywords must be separated by semi-colons.
HELP_MULTIKEY	Displays the topic specified by a keyword in an alternative keyword table.	Address of a MULTIKEYHELP structure that specifies a table footnote character and a keyword.
HELP_PARTIALKEY	Displays the topic in the keyword table that matches the specified keyword if there is an exact match. If there is more than one match, this command displays the Topics Found dialog box. To display the Index without passing a keyword, you should use a pointer to an empty string.	Address of a keyword string. Multiple keywords must be separated by semi-colons.
HELP_QUIT	Informs the HelpExplorer program that it is no longer needed. If no other programs have asked for Help, Windows closes Help Explorer Viewer.	Ignored.
HELP_SETCONTENTS	Specifies the Contents topic. Help Explorer Viewer displays this topic when the user clicks the Contents button if the Help file does not have an associated .CNT file.	Unsigned long integer containing the context identifier for the Contents topic.
HELP_SETPOPUP_POS	Sets the position of the subsequent popup window.	Contains the position data. Use the MakeLong macro to concatenate the horizontal and vertical coordinates into a single value. The popup window is positioned as if the mouse cursor were at the specified point when the popup window was invoked.
HELP_SETWINPOS	Displays the Help window, if it is minimized or in memory, and sets its size and position as specified.	Address of a HELPWININFO structure that specifies the size and position of either a primary or secondary Help window.
HELP_TCARD	Indicates that a command is for a training card instance of the HelpExplorer program. A program combines the HELP_TCARD flag with other commands by using the bitwise OR operator.	Depends on the command with which the flag is combined.
HELP_WM_HELP	Displays, in a popup window, the topic for the control identified by hWnd.	Address of an array of double word pairs. The first double word in each pair is a control identifier, and the second is a context identifier for a topic.
HELP_TAB	Opens the Help Topics dialog box, displaying the specified extensible tab.	Zero-based index of the extensible tab to display (0 is the first tab, 1 the second, etc.).

For example, to provide a Help menu command that invokes the application help, use the following syntax:

InvokeHelp(handle, "myapp.chm", HELP_FINDER, 0)

Resolving Compatibility Issues

When viewing files in Windows Help format in Help Explorer Viewer under Windows and Linux, you may encounter the following common problems that concern compatibility between these operating systems.

Case-sensitive file names in Linux

Linux file systems are case-sensitive, while Windows file systems are case-insensitive. So, if you want to view a help file under Linux, it is very important to ensure that links to external files in the help project are given in the same case as the actual files stored on disk have.

If you are going to use third-party help files without recompiling them, you will not be able to ensure such correspondence. To solve this problem for such files, use the file aliasing mechanism supported by Help Explorer Viewer. It means that for each actual file name, which might be valid under Windows and invalid under Linux, you can specify one or several alias file names which will be definitely valid under Linux.

To use the file aliasing, create the [Setup/File Aliases] section in Help Explorer Viewer's configuration file .helpexplorerc and populate the alias list in the following way:

Real-File-Name=Alias-File-Name[; Alias-File-Name]

For example:

WinHelp32.hlp=winhelp32.hlp
MyHelp.HLP=MYHELP.HLP
MyApplication=myappV1.hlp;myappV2.chm;myappV3.hxs

The following rule applies: if a file with a real name is not found, Help Explorer Viewer tries to open the file by its alias. If there are several aliases specified for a file, Help Explorer Viewer will search for the file in the order its aliases are given (from left to the right) until the file is found.

Missed fonts

This problem is related to a situation when fonts specified in a help file do not exist in the operating system under which you are viewing this help file. This situation can occur not only under Linux, but also under Windows.

To solve this problem, use the font aliasing mechanism supported by Help Explorer Viewer. This mechanism enables substitution of a font announced in the help file with any other font installed in the target operating system without recompiling the help file.

To use the font aliasing, create the [Setup/Font Aliases] section in Help Explorer Viewer's configuration file .helpexplorerc. In this section, specify what fonts that reside in your operating system are to be used instead of the ones announced in help files. The format of each line is

Key=Value,

• where Key is a font specified in the help and Value is a font that will replace it.

For example:

Helvetica=Fixed
Verdana=Fixed