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The CreateNamedPipe function creates an instance of a named pipe and returns a handle for
subsequent pipe operations. A named pipe server process uses this function either to
create the first instance of a specific named pipe and establish its basic
attributes or to create a new instance of an existing named pipe.
Points to the null-terminated string that uniquely identifies the pipe. The
string must have the following form:
The pipename part of the name can include any character other than a backslash, including
numbers and special characters. The entire pipe name string can be up to 256
characters long. Pipe names are not case sensitive.
Specifies the pipe access mode, the overlapped mode, the write-through mode,
and the security access mode of the pipe handle.
This parameter must specify one of the following pipe access mode flags. The
same mode must be specified for each instance of the pipe:
| LPCTSTR lpName,
||// pointer to pipe name
| DWORD dwOpenMode,
||// pipe open mode
| DWORD dwPipeMode,
||// pipe-specific modes
| DWORD nMaxInstances,
||// maximum number of instances
| DWORD nOutBufferSize,
||// output buffer size, in bytes
| DWORD nInBufferSize,
||// input buffer size, in bytes
| DWORD nDefaultTimeOut,
||// time-out time, in milliseconds
| LPSECURITY_ATTRIBUTES lpSecurityAttributes
||// pointer to security attributes structure
This parameter can also include either or both of the following flags, which
enable write-through mode and overlapped mode. These modes can be different for
different instances of the same pipe.
||The pipe is bidirectional; both server and client processes can read from and
write to the pipe. This mode gives the server the equivalent of GENERIC_READ |
GENERIC_WRITE access to the pipe. The client can specify GENERIC_READ or
GENERIC_WRITE, or both, when it connects to the pipe using the CreateFile function.
||The flow of data in the pipe goes from client to server only. This mode gives
the server the equivalent of GENERIC_READ access to the pipe. The client must
specify GENERIC_WRITE access when connecting to the pipe.
||The flow of data in the pipe goes from server to client only. This mode gives
the server the equivalent of GENERIC_WRITE access to the pipe. The client must
specify GENERIC_READ access when connecting to the pipe.
||Write-through mode is enabled. This mode affects only write operations on
byte-type pipes and, then, only when the client and server processes are on
different computers. If this mode is enabled, functions writing to a named pipe do not
return until the data written is transmitted across the network and is in the
pipe's buffer on the remote computer. If this mode is not enabled, the system
enhances the efficiency of network operations by buffering data until a minimum
number of bytes accumulate or until a maximum time elapses.
This parameter can include any combination of the following security access
mode flags. These modes can be different for different instances of the same
pipe. They can be specified without concern for what other dwOpenMode modes have been specified.
||Overlapped mode is enabled. If this mode is enabled, functions performing
read, write, and connect operations that may take a significant time to be
completed can return immediately. This mode enables the thread that started the
operation to perform other operations while the time-consuming operation executes in
the background. For example, in overlapped mode, a thread can handle
simultaneous input and output (I/O) operations on multiple instances of a pipe or perform
simultaneous read and write operations on the same pipe handle. If overlapped
mode is not enabled, functions performing read, write, and connect operations on
the pipe handle do not return until the operation is finished. The ReadFileEx and WriteFileEx functions can only be used with a pipe handle in overlapped mode. The ReadFile, WriteFile, ConnectNamedPipe, and TransactNamedPipe functions can execute either synchronously or as overlapped operations.
Specifies the type, read, and wait modes of the pipe handle.
One of the following type mode flags can be specified. The same type mode must
be specified for each instance of the pipe. If you specify zero, the parameter
defaults to byte-type mode.
||The caller will have write access to the named pipe's discretionary access
control list (ACL).
||The caller will have write access to the named pipe's owner.
||The caller will have write access to the named pipe's system ACL.
One of the following read mode flags can be specified. Different instances of
the same pipe can specify different read modes. If you specify zero, the
parameter defaults to byte-read mode.
||Data is written to the pipe as a stream of bytes. This mode cannot be used
||Data is written to the pipe as a stream of messages. This mode can be used
with either PIPE_READMODE_MESSAGE or PIPE_READMODE_BYTE.
One of the following wait mode flags can be specified. Different instances of
the same pipe can specify different wait modes. If you specify zero, the
parameter defaults to blocking mode.
||Data is read from the pipe as a stream of bytes. This mode can be used with
either PIPE_TYPE_MESSAGE or PIPE_TYPE_BYTE.
||Data is read from the pipe as a stream of messages. This mode can be only used
if PIPE_TYPE_MESSAGE is also specified.
Specifies the maximum number of instances that can be created for this pipe.
The same number must be specified for all instances. Acceptable values are in
the range 1 through PIPE_UNLIMITED_INSTANCES. If this parameter is
PIPE_UNLIMITED_INSTANCES, the number of pipe instances that can be created is limited only by
the availability of system resources.
Specifies the number of bytes to reserve for the output buffer. For a
discussion on sizing named pipe buffers, see the following Remarks section.
Specifies the number of bytes to reserve for the input buffer. For a
discussion on sizing named pipe buffers, see the following Remarks section.
Specifies the default time-out value, in milliseconds, if the WaitNamedPipe function specifies NMPWAIT_USE_DEFAULT_WAIT. Each instance of a named pipe
must specify the same value.
Pointer to a SECURITY_ATTRIBUTES structure that specifies a security descriptor for the new named pipe and
determines whether child processes can inherit the returned handle. If lpSecurityAttributes is NULL, the named pipe gets a default security descriptor and the handle
cannot be inherited.
If the function succeeds, the return value is a handle to the server end of a
named pipe instance.
If the function fails, the return value is INVALID_HANDLE_VALUE. To get
extended error information, call GetLastError. The return value is ERROR_INVALID_PARAMETER if nMaxInstances is greater than PIPE_UNLIMITED_INSTANCES.
To create an instance of a named pipe by using CreateNamedPipe, the user must have FILE_CREATE_PIPE_INSTANCE access to the named pipe
object. If a new named pipe is being created, the access control list (ACL) from the
security attributes parameter defines the discretionary access control for the
All instances of a named pipe must specify the same pipe type (byte-type or
message-type), pipe access (duplex, inbound, or outbound), instance count, and
time-out value. If different values are used, this function fails and GetLastError returns ERROR_ACCESS_DENIED.
The input and output buffer sizes are advisory. The actual buffer size
reserved for each end of the named pipe is either the system default, the system
minimum or maximum, or the specified size rounded up to the next allocation
An instance of a named pipe is always deleted when the last handle to the
instance of the named pipe is closed.
ConnectNamedPipe, CreateFile, ReadFile, ReadFileEx, SECURITY_ATTRIBUTES, TransactNamedPipe, WaitNamedPipe, WriteFile, WriteFileEx
||Blocking mode is enabled. When the pipe handle is specified in the ReadFile, WriteFile, or ConnectNamedPipe function, the operations are not completed until there is data to read, all
data is written, or a client is connected. Use of this mode can mean waiting
indefinitely in some situations for a client process to perform an action.
||Nonblocking mode is enabled. In this mode, ReadFile, WriteFile, and ConnectNamedPipe always return immediately. Note that nonblocking mode is supported for
compatibility with Microsoft LAN Manager version 2.0 and should not be used to
achieve asynchronous I/O with named pipes.
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