// 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 "".
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.
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).
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
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.
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.
zstr_recvx (void *source, char **string_p, ...);
// Free a provided string, and nullify the parent pointer. Safe to call on
// a null pointer.
zstr_free (char **string_p);
// Self test of this class
zstr_test (bool verbose);