# TCPX Flags2

> [HTML Version](tcpxflags2.htm)

This table lists all of the _opcodes_ and describes the interpretation of the _flags_ parameter for each. Note that in several cases, such as with the read, write and check operations, the value of _flags_ relates to a number of data bytes, rather than to bit values as in the Flags1 table..

| **Opcode** | **Interpretation of **_Flags_** Parameter** |
|------|------|
| TCPOP\_ACCEPT | TCPXFLG\_BLOCK sets blocking mode, which means that read and write calls wait until they can be completed or the timer expires; in non-blocking mode, if _timer_=0 and the read/write operation cannot be immediately completed, an error status is returned.  |
| TCPOP\_WRITE | Specifies the number of bytes to write. Must be less than or equal to the size of _buffer_, unless _buffer_ is subscripted, in which case we just trust the _flags_ value. If _flags_=0 (or not specified), writes the entire _buffer_ block. If _flags_ non-zero, the specified number of bytes are written. In order to minimize partial packet writes, we set the send buffer low water mark to match the number of bytes to write, so that we do not start the operation unless the socket buffer has sufficient space. If _timer_ > 0, it waits until the timer expires or the packet is fully written. If _timer_ = 0 and the connection is non-blocking, it returns an error ("EWOULDBLOCK") if the packet cannot be written immediately. Otherwise it waits indefinitely, for the packet to be entirely written or the socket is closed at the other end. This is one case where you might have a problem if you use a packet size larger than the OS supports. |
| TCPOP\_READ | Specifies the number of bytes to read. 0 means read whatever is available, from 1 byte to size of buffer. Otherwise, if timer > 0, routine will wait until the required number of bytes is read up to the time limit. If timer = 0 and flags > 0, for non-blocking connections, the flags value is only an upper limit; the routine will return as soon as the interface indicates there is data available even if not the requested number of bytes. For blocking connections, with timer = 0 and flags > 0, the subroutine will wait until the # of bytes is received, or the socket is closed at the other end. <br>If both flags = 0 and timer = 0, for blocking connections it should wait until any data or an error condition is available. For non-blocking connections, the behavior may be platform dependent. Under Unix and Windows, it should return immediately, either with data or with Unix error -11 (resource temporarily unavailable) or Windows error -10035 (a non-blocking socket operation could not be completed immediately). Under some versions of AIX, it has been reported to act the same as for a blocking connection—i.e. waiting until data or some other error is available. If this is a critical concern for your application, you should test it under the platform you will be using. See the test program [TCPTST in EXLIB:\[908,25\]](https://bitbucket.org/microsabio/exlib/src/master/908025/tcptst.bp) to simplify your testing. |
| TCPOP\_SHUTDOWN | 0 indicates a shutdown in both directions. Otherwise, you can shut down just one direction by specifying either TCPXFLG\_SHUTRD (32) or TXPXFLG\_SHUTWR (64). |
| TCPOP\_CLOSE | _flags_ not used. |
| TCPOP\_CHECK | If _timer_ specified, _flags_ is ignored and _timer_ is used. If _timer_ not specified, _flags_ specifies how long to wait before returning _status_ 0 if no data avail. If _flags_ is F,6 then it is interpreted as fractional seconds; otherwise it is interpreted as milliseconds. (You should specify _timer_ in all new programs; the option to exclude it is only supported for backward compatibility with TCPCLI and TCPSRV, and is deprecated.) See [Asynchronous Client Connections](asynchronousclientcon.htm.md) for special considerations involving _flags_ and TCPOP\_CHECK. |
| TCPOP\_CHKQTY | _flags_ not used.  |
| TCPOP\_CONNECT | TCPXFLG\_BLOCK sets blocking connection (see TCPOP\_ACCEPT)<br>TCPXFLG\_ASYNC sets asynchronous mode (see [Asynchronous Client Connections](asynchronousclientcon.htm.md)). |
| TCPOP\_CONNECT\_OLD | TCPXFLG\_BLOCK sets blocking connection (see TCPOP\_ACCEPT) |
| TCPOP\_ERRMSG | _flags_ not used.  |
| TCPOP\_STARTTLS | STARTTLS (engage TLS mode) |
| TCPOP\_WRITE\_UDP | UDP version of WRITE |
| TCPOP\_READ\_UDP | UDP version of READ |