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IDL Reference Guide: Procedures and Functions |
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The SOCKET procedure opens a client-side TCP/IP Internet socket as an IDL file unit. Such files can be used in the standard manner with any of IDL's Input/Output routines.
| Tip Avoid using the EOF procedure as a way to check to see if a socket is empty. Instead, structure your communication across the socket so that using EOF is not necessary to know when the communication is complete. |
SOCKET, Unit, Host, Port [, CONNECT_TIMEOUT=value] [, ERROR=variable] [, /GET_LUN] [, /RAWIO] [, READ_TIMEOUT=value] [, /SWAP_ENDIAN] [, /SWAP_IF_BIG_ENDIAN] [, /SWAP_IF_LITTLE_ENDIAN] [, WIDTH=value] [, WRITE_TIMEOUT=value]
UNIX-Only Keywords: [, /STDIO]
The unit number to associate with the opened socket.
The name of the host to which the socket is connected. This can be either a standard Internet host name (e.g. ftp.ittvis.com) or a dot-separated numeric address (e.g. 192.5.156.21).
The port to which the socket is connected on the remote machine. If this is a well-known port (as contained in the /etc/services file on a UNIX host), then you can specify its name (e.g. daytime); otherwise, specify a number.
Set this keyword to the number of seconds to wait before giving up and issuing an error to shorten the connect timeout from the system-supplied default. Most experts recommend that you not specify an explicit timeout, and instead use your operating system defaults.
| Note Although you can use CONNECT_TIMEOUT to shorten the timeout, you cannot increase it past the system-supplied default. |
A named variable in which to place the error status. If an error occurs in the attempt to the socket, IDL normally takes the error handling action defined by the ON_ERROR and/or ON_IOERROR procedures. SOCKET always returns to the caller without generating an error message when ERROR is present. A nonzero error status indicates that an error occurred. The error message can then be found in the system variable !ERROR_STATE.MSG.
Set this keyword to use the GET_LUN procedure to set the value of Unit before the file is opened. Instead of using the two statements:
GET_LUN, Unit OPENR, Unit, 'data.dat'
you can use the single statement:
OPENR, Unit, 'data.dat', /GET LUN
Set this keyword to disable all use of the standard operating system I/O for the file, in favor of direct calls to the operating system. This allows direct access to devices, such as tape drives, that are difficult or impossible to use effectively through the standard I/O. Using this keyword has the following implications:
Set this keyword to the number of seconds to wait for data to arrive before giving up and issuing an error. By default, IDL blocks indefinitely until the data arrives. Typically, this option is unnecessary on a local network, but it is useful with networks that are slow or unreliable.
This keyword is only available on UNIX platforms.
Under UNIX, forces the file to be opened via the standard C I/O library (stdio) rather than any other more native OS API that might usually be used. This is primarily of interest to those who intend to access the file from external code, and is not necessary for most uses.
| Note Under Windows, the STDIO feature is not possible. Requesting it causes IDL to throw an error. |
Set this keyword to swap byte ordering for multi-byte data when performing binary I/O on the specified file. This is useful when accessing files also used by another system with byte ordering different than that of the current host.
Setting this keyword is equivalent to setting SWAP_ENDIAN; it only takes effect if the current system has big endian byte ordering. This keyword does not refer to the byte ordering of the input data, but to the computer hardware.
Setting this keyword is equivalent to setting SWAP_ENDIAN; it only takes effect if the current system has little endian byte ordering. This keyword does not refer to the byte ordering of the input data, but to the computer hardware.
The desired output width. When using the defaults for formatted output, IDL uses the following rules to determine where to break lines:
The WIDTH keyword allows the user to override this default.
Set this keyword to the number of seconds to wait to send data before giving up and issuing an error. By default, IDL blocks indefinitely until it is possible to send the data. Typically, this option is unnecessary on a local network, but it is useful with networks that are slow or unreliable.
Most UNIX systems maintain a daytime server on the daytime port (port 13). These servers send a 1 line response when connected to, containing the current time of day.
; To obtain the current time from the host bullwinkle: SOCKET, 1, 'bullwinkle','daytime' date='' READF, 1, date CLOSE, 1 PRINT, date
IDL prints: