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Performs an operation on a specified file.

Syntax

Parameters

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hwnd

Type: HWND

A handle to the parent window used for displaying a UI or error messages. This value can be NULL if the operation is not associated with a window.

lpOperation

Type: LPCTSTR

A 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. 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 a folder specified by lpFile.

find

Initiates a search beginning in the directory specified by lpDirectory.

open

Dev Null Command

Opens the item specified by the lpFile parameter. The item can be a file or folder.

print

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

runas

Launches an application as Administrator. User Account Control (UAC) will prompt the user for consent to run the application elevated or enter the credentials of an administrator account used to run the application.

NULL

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

Type: LPCTSTR

A 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. If a relative path is used for the lpDirectory parameter do not use a relative path for lpFile.

lpParameters

Type: LPCTSTR

If lpFile specifies an executable file, this parameter 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

Type: LPCTSTR

A pointer to a null-terminated string that specifies the default (working) directory for the action. If this value is NULL, the current working directory is used. If a relative path is provided at lpFile, do not use a relative path for lpDirectory.

nShowCmd

Type: INT

The 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. These values are defined in Winuser.h.

SW_HIDE (0)

Hides the window and activates another window.

SW_MAXIMIZE (3)

Maximizes the specified window.

SW_MINIMIZE (6)

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

SW_RESTORE (9)

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 (5)

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

SW_SHOWDEFAULT (10)

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 (3)

Activates the window and displays it as a maximized window.

SW_SHOWMINIMIZED (2)

Activates the window and displays it as a minimized window.

SW_SHOWMINNOACTIVE (7)

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

SW_SHOWNA (8)

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

SW_SHOWNOACTIVATE (4)

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

SW_SHOWNORMAL (1)

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

Type: HINSTANCE

If the function succeeds, it returns a value greater than 32. If the function fails, it returns an error value that indicates the cause of the failure. The return value is cast as an HINSTANCE for backward compatibility with 16-bit Windows applications. It is not a true HINSTANCE, however. It can be cast only to an int and compared to either 32 or the following error codes below.

Remarks

Because ShellExecute can delegate execution to Shell extensions (data sources, context menu handlers, verb implementations) that are activated using Component Object Model (COM), COM should be initialized before ShellExecute is called. Some Shell extensions require the COM single-threaded apartment (STA) type. In that case, COM should be initialized as shown here:

There are certainly instances where ShellExecute does not use one of these types of Shell extension and those instances would not require COM to be initialized at all. Nonetheless, it is good practice to always initalize COM before using this function.

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:

or

To explore a folder, use the following call:

To launch the Shell's Find utility for a directory, use the following call.

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 shellapi.h header defines ShellExecute as an alias which automatically selects the ANSI or Unicode version of this function based on the definition of the UNICODE preprocessor constant. Mixing usage of the encoding-neutral alias with code that not encoding-neutral can lead to mismatches that result in compilation or runtime errors. For more information, see Conventions for Function Prototypes.

Requirements

See also

C++ Is Null

/dev/zero is a special file in Unix-likeoperating systems that provides as many null characters (ASCII NUL, 0x00) as are read from it.^[1] One of the typical uses is to provide a character stream for initializing data storage.^[2]

Function[edit]

Read operations from /dev/zero return as many null characters (0x00) as requested in the read operation.

Unlike /dev/null, /dev/zero may be used as a source, not only as a sink for data. All write operations to /dev/zero succeed with no other effects. However, /dev/null is more commonly used for this purpose.

When /dev/zero is memory-mapped, e.g., with mmap, to the virtual address space, it is equivalent to using anonymous memory; i.e. memory not connected to any file.

History[edit]

/dev/zero was introduced in 1988 by SunOS-4.0 in order to allow a mappable BSS segment for shared libraries using anonymous memory.^[3] HP-UX 8.x introduced the MAP_ANONYMOUS flag for mmap(), which maps anonymous memory directly without a need to open /dev/zero.^[4] Since the late 1990s, MAP_ANONYMOUS^[5] or MAP_ANON are supported by most UNIX versions, removing the original purpose of /dev/zero.^[6]

Examples[edit]

The dd Unix utility program reads octet streams from a source to a destination, possibly performing data conversions in the process.Destroying existing data on a file system partition (low-level formatting):

C++ Null Type

Creating a 1 MiB file, called foobar, filled with null characters:^[7]

Note: The block size value can be given in SI (decimal) values, e.g. in GB, MB, etc. To create a 1 GB file one would simply type:

Note: Instead of creating a real file with only zero bytes, many file systems also support the creation of sparse files which returns zeros upon reading but use less actual space.^[8]

See also[edit]

• /dev
• /dev/null
• /dev/full

References[edit]

1. ^Mitchell, Mark; Oldham, Jeffrey; Samuel, Alex (2001), '6.5.2 /dev/zero', Advanced Linux Programming, Sams Publishing, p. 136, ISBN9780735710436
2. ^Love, Robert (2007), 'Mapping /dev/zero', Linux System Programming: Talking Directly to the Kernel and C Library, O'Reilly Media, Inc., pp. 259–260, ISBN9780596009588
3. ^''C' run-time program bootstrap from SunOS, contributed to CSRG for inclusion in 4.4BSD'. TUHS.
4. ^'HP-UX 8.0.7 install media'.
5. ^Beal, Chris. 'So what the heck is anonymous memory'. Oracle Blog.
6. ^'MAP_ANON description in mmap(2)'. NetBSD.
7. ^Optimizing NFS Performance: Tuning and Troubleshooting NFS on HP-UX Systems, Dave (2002). Olker. Prentice Hall Professional. pp. 26–7. ISBN9780130428165. Retrieved 2014-07-16.
8. ^Sparse file

C++ Not Null