Running applications from Delphi^TM: Using ShellExecute (Part 1)

Level: Newbie-Hacker
Author: The Baker
Date: 2002-04-19

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> Overview
> Running applications from Delphi
> ShellExecute WinAPI
> Operation Type
> Show Command
> Using ShellExecute
> Conclusion
> Further Reading

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Running or opening external programs or files, from Delphi^TM applications, is often a necessary requirement. This article covers the ShellExecute Windows API function, revealing techniques for running external applications from your Delphi applications.

Running applications from Delphi

There are a number of reasons why you might be interested in running external applications from your Delphi application. Often programs are segmented into a number of logical divisions to represent different components of a larger system. Some sub-system components might include:

· Main application

· Setup/Installer application

· System application (specifying system wide options)

· Application server application

· Reporting application

· an external third party application

As can be seen, there are a number of reasons why you might need to call an external application. Let's discuss how we can do this with the ShellExecute command.

ShellExecute WinAPI

The ShellExecute API allows for the execution (or "running") of external applications. It also has a number of other uses, however these all involve performing operations on external files. The syntax for the ShellExecute WinAPI function is:

HINSTANCE ShellExecute(HWND hwnd,
     LPCTSTR lpOperation,
     LPCTSTR lpFile,
     LPCTSTR lpParameters,
     LPCTSTR lpDirectory,
     INT nShowCmd
);

The following is a description of the parameters for the ShellExecute function.

*Parameter*	*Input/Output*	*Description*
hwnd	input	Handle to the parent window: needed for error reporting.
lpOperation	input	Pointer to a null-terminated string. This is the action to be performed (the "object verb")
lpFile	input	Pointer to a null-terminated string that specifies the file or object to execute the specified verb on.
lpParameters	input	Pointer to a null-terminated string that specifies the parameters to be passed to the application (if the lpFile is an application file). Otherwise, this should be NULL.
lpDirectory	input	Pointer to a null-terminated string that specifies the default directory.
nShowCmd	input	Flag determining how the application window will be displayed when it is opened.

The ShellExecute function will return an error code if the function fails. This can be retrieved using the GetLastError function. If the error code is greater than 32, then the function was successful. If it less than or equal to 32 then an error has occurred. For a complete listing of the error codes refer to the MSDN website (link provided in the further reading section).

The easiest way to interpret the error code is with the SysErrorMessage(GetLastError) function call. This will map the appropriate Windows error message returned by the GetLastError API function.

if ShellExecute(Handle, 'print', PChar('c:\log.txt'), nil, nil, SW_SHOWNORMAL) <= 32 then
ShowMessage(SysErrorMessage(GetLastError));

Operation Type

The ShellExecute function allows for operations to be executed on programs and application objects. In some cases, objects may not be able to respond to an operation type. For example, not all document types support the "print" verb. A list of the commonly supported verbs include:

*lpOperation Value*	*Result Description*
edit	Opens a document for editing in an editor.
explore	Explores the folder, using Windows Explorer, specified by the lpFile parameter.
find	Opens the Search form initiating a search starting from the directory specified in the lpFile parameter.
open	Opens the file, application or folder specified by the lpFile parameter.
print	Prints the document file specified by lpFile parameter.
NULL	More information below

If NULL is specified then different functionality will occur depending on the operating system version. The following is an extract from the MSDN ShellExecute document:

For systems prior to Microsoft® Windows® 2000, the default verb is used if it is valid and available in the registry. If not, the "open" verb is used.
For Windows 2000 and later systems, the default verb is used if available. If not, the "open" verb is used. If neither verb is available, the system uses the first verb listed in the registry.

If I use the "open" verb on a .PAS file, nothing happens. If I use NULL instead, then the .PAS file will be opened in Delphi. The registry defines the application that is associated with the .PAS file.

Show Command

The ShellExecute requires the nShowCmd type. This represents how the new window will be displayed when it is created via the ShellExecute call.

*nShowCmd Value*	*Result Description*
SW_HIDE	Hides the window and activates another window.
SW_MAXIMIZE	Maximizes the specified window.
SW_MINIMIZE	Minimizes the specified window and activates the next top-level window in the z-order.
SW_RESTORE	Activates and displays the window. If the window is minimized or maximized, Windows restores it to its original size and position. An application should specify this flag when restoring a minimized window.
SW_SHOW	Activates the window and displays it in its current size and position.
SW_SHOWDEFAULT	Sets the show state based on the SW_ flag specified in the STARTUPINFO structure passed to the CreateProcess function by the program that started the application. An application should call ShowWindow with this flag to set the initial show state of its main window.
SW_SHOWMAXIMIZED	Activates the window and displays it as a maximized window.
SW_SHOWMINIMIZED	Activates the window and displays it as a minimized window.
SW_SHOWMINNOACTIVE	Displays the window as a minimized window. The active window remains active.
SW_SHOWNA	Displays the window in its current state. The active window remains active.
SW_SHOWNOACTIVATE	Activates and displays a window. Windows restores it to its original size and position. The active window remains active.
SW_SHOWNORMAL	Activates and displays a window. Windows restores it to its original size and position.

When you call an application for the first time you should call the SW_SHOWNORMAL flag.

Using ShellExecute

The following is a list of ShellExecute uses. You will need to add the Windows and ShellAPI units to the uses clause.

Run an application called Demo.exe in "C:\apps" directory:

ShellExecute(Handle,NIL,PChar('C:\apps\demo.exe'), nil,nil,SW_SHOWNORMAL);

Open a file (e.g. "log.txt"):

ShellExecute(Handle,'open',PChar('c:\log.txt'), nil,nil,SW_SHOWNORMAL);

Play a music file (e.g. "ending.mp3"):

ShellExecute(Handle,'play',PChar('c:\ending.mp3'), nil,nil,SW_SHOWNORMAL);

Print a log file (e.g. "log.txt"):

ShellExecute(Handle,'print',PChar('c:\log.txt'), nil,nil,SW_SHOWNORMAL);

Open up Windows Explorer on C Drive (e.g. "c:"):

ShellExecute(Handle,'explore',PChar('c:\'), nil,nil,SW_SHOWNORMAL);

Create a new email message with Outlook or Outlook express:

ProcedureCreateEmail(Const EmailAddr, Subject, Body: String);
var
  ConcatEmailStr: String;
Begin
  ConcatEmailStr := EmailAddr + '?subject=' + Subject + '&body=' + Body;

  ShellExecute(Handle,'open',PChar(ConcatEmailStr), nil, nil, SW_SHOWNORMAL);
end;

Conclusion

I hope this article has provided you with a greater insight into running applications from Delphi and the ShellExecute WinAPI function. In the next article I will discuss how to wait for an application to finish before resuming application execution.

ShellExecute Function

Performs an operation on a specified file.

Syntax

HINSTANCE ShellExecute(      

    HWND hwnd,

    LPCTSTR lpOperation,

    LPCTSTR lpFile,

    LPCTSTR lpParameters,

    LPCTSTR lpDirectory,

    INT nShowCmd

);

Parameters

hwnd

[in] Handle to a parent window. This window receives any message boxes that an application produces, such as error reporting.

lpOperation

[in] Pointer to a null-terminated string, referred to in this case as a verb, that specifies the action to be performed. The set of available verbs depends on the particular file or folder. Generally, the actions available from an object's shortcut menu are available verbs. For more information about verbs and their availability, see Object Verbs. See Extending Shortcut Menus for further discussion of shortcut menus. The following verbs are commonly used.

edit

Launches an editor and opens the document for editing. If lpFile is not a document file, the function will fail.

explore

Explores the folder specified by lpFile.

find

Initiates a search starting from the specified directory.

open

Opens the file specified by the lpFile parameter. The file can be an executable file, a document file, or a folder.

Prints the document file specified by lpFile. If lpFile is not a document file, the function will fail.

NULL

For systems prior to Microsoft® Windows® 2000, the default verb is used if it is valid and available in the registry. If not, the "open" verb is used.

For Windows 2000 and later systems, the default verb is used if available. If not, the "open" verb is used. If neither verb is available, the system uses the first verb listed in the registry.

lpFile

[in] Pointer to a null-terminated string that specifies the file or object on which to execute the specified verb. To specify a Shell namespace object, pass the fully qualified parse name. Note that not all verbs are supported on all objects. For example, not all document types support the "print" verb.

lpParameters

[in] If the lpFile parameter specifies an executable file, lpParameters is a pointer to a null-terminated string that specifies the parameters to be passed to the application. The format of this string is determined by the verb that is to be invoked. If lpFile specifies a document file, lpParameters should be NULL.

lpDirectory

[in] Pointer to a null-terminated string that specifies the default directory.

nShowCmd

[in] Flags that specify how an application is to be displayed when it is opened. If lpFile specifies a document file, the flag is simply passed to the associated application. It is up to the application to decide how to handle it.

SW_HIDE

Hides the window and activates another window.

SW_MAXIMIZE

Maximizes the specified window.

SW_MINIMIZE

Minimizes the specified window and activates the next top-level window in the z-order.

SW_RESTORE

Activates and displays the window. If the window is minimized or maximized, Windows restores it to its original size and position. An application should specify this flag when restoring a minimized window.

SW_SHOW

Activates the window and displays it in its current size and position.

SW_SHOWDEFAULT

Sets the show state based on the SW_ flag specified in the STARTUPINFO structure passed to the CreateProcess function by the program that started the application. An application should call ShowWindow with this flag to set the initial show state of its main window.

SW_SHOWMAXIMIZED

Activates the window and displays it as a maximized window.

SW_SHOWMINIMIZED

Activates the window and displays it as a minimized window.

SW_SHOWMINNOACTIVE

Displays the window as a minimized window. The active window remains active.

SW_SHOWNA

Displays the window in its current state. The active window remains active.

SW_SHOWNOACTIVATE

Displays a window in its most recent size and position. The active window remains active.

SW_SHOWNORMAL

Activates and displays a window. If the window is minimized or maximized, Windows restores it to its original size and position. An application should specify this flag when displaying the window for the first time.

Return Value

Returns a value greater than 32 if successful, or an error value that is less than or equal to 32 otherwise. The following table lists the error values. The return value is cast as an HINSTANCE for backward compatibility with 16-bit Windows applications. It is not a true HINSTANCE, however. The only thing that can be done with the returned HINSTANCE is to cast it to an int and compare it with the value 32 or one of the error codes below.

0	The operating system is out of memory or resources.
ERROR_FILE_NOT_FOUND	The specified file was not found.
ERROR_PATH_NOT_FOUND	The specified path was not found.
ERROR_BAD_FORMAT	The .exe file is invalid (non-Microsoft Win32® .exe or error in .exe image).
SE_ERR_ACCESSDENIED	The operating system denied access to the specified file.
SE_ERR_ASSOCINCOMPLETE	The file name association is incomplete or invalid.
SE_ERR_DDEBUSY	The Dynamic Data Exchange (DDE) transaction could not be completed because other DDE transactions were being processed.
SE_ERR_DDEFAIL	The DDE transaction failed.
SE_ERR_DDETIMEOUT	The DDE transaction could not be completed because the request timed out.
SE_ERR_DLLNOTFOUND	The specified dynamic-link library (DLL) was not found.
SE_ERR_FNF	The specified file was not found.
SE_ERR_NOASSOC	There is no application associated with the given file name extension. This error will also be returned if you attempt to print a file that is not printable.
SE_ERR_OOM	There was not enough memory to complete the operation.
SE_ERR_PNF	The specified path was not found.
SE_ERR_SHARE	A sharing violation occurred.

Remarks

This method allows you to execute any commands in a folder's shortcut menu or stored in the registry.

To open a folder, use either of the following calls:

ShellExecute(handle, NULL, <fully_qualified_path_to_folder>, NULL, NULL, SW_SHOWNORMAL);

ShellExecute(handle, "open", <fully_qualified_path_to_folder>, NULL, NULL, SW_SHOWNORMAL);

To explore a folder, use:

ShellExecute(handle, "explore", <fully_qualified_path_to_folder>, NULL, NULL, SW_SHOWNORMAL);

To launch the Shell's Find utility for a directory, use:

ShellExecute(handle, "find", <fully_qualified_path_to_folder>, NULL, NULL, 0);

If lpOperation is NULL, the function opens the file specified by lpFile. If lpOperation is "open" or "explore", the function attempts to open or explore the folder.

To obtain information about the application that is launched as a result of calling ShellExecute, use ShellExecuteEx.

Note The Launch folder windows in a separate process setting in Folder Options affects ShellExecute. If that option is disabled (the default setting), ShellExecute uses an open Explorer window rather than launch a new one. If no Explorer window is open, ShellExecute launches a new one.

Windows 95/98/Me: ShellExecute is supported by the Microsoft Layer for Unicode. To use this, you must add certain files to your application, as outlined in Microsoft Layer for Unicode on Windows 95/98/Me Systems.

Function Information

Header	shellapi.h
Import library	shell32.lib
Minimum operating systems	Windows NT 3.1, Windows 95

Running applications from DelphiTM: Using ShellExecute (Part 1)