0MQ Api

//  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);