DosPeekMailslot or Dos32PeekMailslot

The DosPeekMailslot API reads the next available message in a mailslot without removing it.

Note: If a higher-priority message arrives, there is no guarantee that a message previously read by the DosPeekMailslot API will be the same message read by a subsequent call to the DosReadMailslot API.

This API can be called from DLS and OS/2 workstations. A call to this API must be issued locally.

#include <netcons.h>
#include <mailslot.h>
 
DosPeekMailslot(mailslothandle, buf, pusBytesReturned,
                  nextsize, nextpriority);     /* 16 bit */
 
Dos32PeekMailslot(mailslothandle, buf, pulBytesReturned,
                  nextsize, nextpriority);     /* 32 bit */

See Common Parameter Definitions for descriptions of parameters not defined here.

mailslothandle

(unsigned long) specifies (by its handle) the mailslot to read.
nextsize
(16-bit unsigned short LSFAR * or 32-bit unsigned long LSFAR *) points to an unsigned short integer indicating the size (in bytes) of the next message in the mailslot. If 0, no message is available.
nextpriority
(16-bit unsigned short LSFAR * or 32-bit unsigned long LSFAR *) points to an unsigned short integer indicating the priority (0-9) of the next message in the mailslot. (This parameter is undefined if nextsize is 0.)

The following table lists the return codes most significant to this API. (See API Return Codes for a complete list of return codes.) ┌─────────────────────────────┬────────────┬───────────────────────────────────┐│SYMBOLICCONSTANT │VALUE │MEANING │
├─────────────────────────────┼────────────┼───────────────────────────────────┤
│ NERR_Success │ 0 │ No errors were encountered. │
├─────────────────────────────┼────────────┼───────────────────────────────────┤
│ ERROR_INVALID_HANDLE │ 6 │ The specified handle is not │
│ │ │ valid. │
├─────────────────────────────┼────────────┼───────────────────────────────────┤
│ ERROR_BROKEN_PIPE │ 109 │ Write on pipe that is not being │
│ │ │ read. │
└─────────────────────────────┴────────────┴───────────────────────────────────┘


Other codes could be returned by the DosSemRequest function.

For information about:

• Reading and removing a message, see Mailslot - DosReadMailslot.
  
• Writing a message to a mailslot, see Mailslot - DosWriteMailslot.

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