zstr(3)

zstr(3)

CZMQ Manual - CZMQ/3.0.1

Name

zstr - sending and receiving strings

Synopsis

//  Receive C string from socket. Caller must free returned string using
//  zstr_free(). Returns NULL if the context is being terminated or the
//  process was interrupted.
CZMQ_EXPORT char *
    zstr_recv (void *source);

//  Send a C string to a socket, as a frame. The string is sent without
//  trailing null byte; to read this you can use zstr_recv, or a similar
//  method that adds a null terminator on the received string. String
//  may be NULL, which is sent as "".
CZMQ_EXPORT int
    zstr_send (void *dest, const char *string);

//  Send a C string to a socket, as zstr_send(), with a MORE flag, so that
//  you can send further strings in the same multi-part message.
CZMQ_EXPORT int
    zstr_sendm (void *dest, const char *string);

//  Send a formatted string to a socket. Note that you should NOT use
//  user-supplied strings in the format (they may contain '%' which
//  will create security holes).
CZMQ_EXPORT int
    zstr_sendf (void *dest, const char *format, ...);

//  Send a formatted string to a socket, as for zstr_sendf(), with a
//  MORE flag, so that you can send further strings in the same multi-part
//  message.
CZMQ_EXPORT int
    zstr_sendfm (void *dest, const char *format, ...);

//  Send a series of strings (until NULL) as multipart data
//  Returns 0 if the strings could be sent OK, or -1 on error.
CZMQ_EXPORT int
    zstr_sendx (void *dest, const char *string, ...);

//  Receive a series of strings (until NULL) from multipart data.
//  Each string is allocated and filled with string data; if there
//  are not enough frames, unallocated strings are set to NULL.
//  Returns -1 if the message could not be read, else returns the
//  number of strings filled, zero or more. Free each returned string
//  using zstr_free(). If not enough strings are provided, remaining
//  multipart frames in the message are dropped.
CZMQ_EXPORT int
    zstr_recvx (void *source, char **string_p, ...);

//  Free a provided string, and nullify the parent pointer. Safe to call on
//  a null pointer.
CZMQ_EXPORT void
    zstr_free (char **string_p);

//  Self test of this class
CZMQ_EXPORT void
    zstr_test (bool verbose);

Description

The zstr class provides utility functions for sending and receiving C strings across ØMQ sockets. It sends strings without a terminating null, and appends a null byte on received strings. This class is for simple message sending.

       Memory                       Wire
       +-------------+---+          +---+-------------+
Send   | S t r i n g | 0 |  ---->   | 6 | S t r i n g |
       +-------------+---+          +---+-------------+
       Wire                         Heap
       +---+-------------+          +-------------+---+
Recv   | 6 | S t r i n g |  ---->   | S t r i n g | 0 |
       +---+-------------+          +-------------+---+

Example

From zstr_test method

// Create two PAIR sockets and connect over inproc
zsock_t *output = zsock_new_pair ("@inproc://zstr.test");
assert (output);
zsock_t *input = zsock_new_pair (">inproc://zstr.test");
assert (input);

// Send ten strings, five strings with MORE flag and then END
int string_nbr;
for (string_nbr = 0; string_nbr < 10; string_nbr++)
 zstr_sendf (output, "this is string %d", string_nbr);
zstr_sendx (output, "This", "is", "almost", "the", "very", "END", NULL);

// Read and count until we receive END
string_nbr = 0;
for (string_nbr = 0;; string_nbr++) {
 char *string = zstr_recv (input);
 assert (string);
 if (streq (string, "END")) {
 zstr_free (&string);
 break;
 }
 zstr_free (&string);
}
assert (string_nbr == 15);

zsock_destroy (&input); zsock_destroy (&output);

See also

czmq(7)

Authors

The CZMQ manual was written by Pieter Hintjens<moc.xitami|hp#moc.xitami|hp>.

Resources

Main web site: http://czmq.zeromq.org/

Report bugs to the ØMQ development mailing list: <gro.qmorez.stsil|ved-qmorez#gro.qmorez.stsil|ved-qmorez>

Copyright

Copyright (c) the Contributors as noted in the AUTHORS file. This file is part of CZMQ, the high-level C binding for ØMQ: http://czmq.zeromq.org. This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0. If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.