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LIBMJ(3)                   Library Functions Manual                   LIBMJ(3)

NAME
     libmj -- minimalist JSON lightweight data interchange library

LIBRARY
     library ``libmj''

SYNOPSIS
     #include <&lt;mj.h>&gt;

     int
     mj_create(mj_t *atom, const char *text, ...);

     int
     mj_parse(mj_t *atom, const char *text, int *tokfrom, int *tokto, int
     *toktype);

     int
     mj_append(mj_t *atom, const char *text, ...);

     int
     mj_append_field(mj_t *atom, const char *fieldname, const char
     *text, ...);

     int
     mj_deepcopy(mj_t *dest, mj_t *src);

     void
     mj_delete(mj_t *atom);

     Access to objects and array entries is made using the following
     functions:
     int
     mj_arraycount(mj_t *atom);

     int
     mj_object_find(mj_t *atom, const char *name, const unsigned startpoint,
     const unsigned incr);

     mj_t *
     mj_get_atom(mj_t *atom, ...);

     JSON object output functions:
     int
     mj_snprint(char *buffer, size_t size, mj_t *atom);

     int
     mj_asprint(char **buffer, mj_t *atom);

     int
     mj_string_size(mj_t *atom);

     int
     mj_pretty(mj_t *atom, void *stream, unsigned depth, const char *trailer);

     const char *
     mj_string_rep(mj_t *atom);

DESCRIPTION
     libmj is a small library interface to allow JSON text to be created and
     parsed.  JSON is the Java Script Object Notation, a lightweight data-
     interchange format, standardised in the ECMA standard.  The library name
     libmj is derived from a further acronym of ``minimalist JSON''.

     The libmj library can be used to create a string in memory which contains
     a textual representation of a number of objects, arbitrarily structured.
     The library can also be used to reconstruct the structure.  Data can thus
     be serialised easily and efficiently, and data structures rebuilt to
     produce the original structure of the data.

     JSON contains basic units called atoms, the two basic atoms being strings
     and numbers.  Three other useful atomic values are provided, ``null'',
     ``false'', and ``true''.  Atoms can be grouped together as key/value
     pairs in an ``object'', and as individual, ordered atoms, in an
     ``array''.

     To create a new object, the mj_create() is used.  It can be deleted using
     the mj_delete() function.

     Atoms, objects and arrays can be appended to arrays and objects using the
     mj_append() function.

     Objects can be printed out by using the mj_snprint() function.  The size
     of a string of JSON text can be calculated using the mj_string_size()
     function.  A utility function mj_asprint() is provided which will
     allocate space dynamically, using calloc(3), and the JSON serialised text
     is copied into it.  This memory can later be de-allocated using free(3).
     For formatted output to a FILE * stream, the mj_pretty() function is
     used.  The calling interface gives the ability to indent the output to a
     given depth and for the formatted output to be followed by a trailer
     string, which is usually NULL for external calls, but can be any valid
     string.  Output is sent to the stream file stream.

     The type argument given to the mj_create(), mj_append(), and
     mj_append_field() functions is taken from a list of ``false'' ``true''
     ``null'' ``number'' ``integer'' ``string'' ``array'' and ``object''
     types.  An integer differs from a number in that it cannot take on any
     floating point values.  It is implemented internally using a signed
     64-bit integer type.  This restriction of values for an integer type may
     be removed at a later date.

     Within a JSON object, the key values can be iterated over using an
     integer index to access the individual JSON objects.  The index can also
     be found using the mj_object_find() function.

     The way objects arrays are implemented in libmj is by using varying-sized
     arrays internally.  Objects have the field name as the even entry in this
     internal array, with the value being the odd entry.  Arrays are
     implemented as a simple array.  Thus, to find an object in an array using
     mj_object_find(), a value of 1 should be used as the increment value.
     This means that every entry in the internal array will be examined, and
     the first match after the starting point will be returned.  For objects,
     an incremental value of 2 should be used, and an even start value should
     be specified.

     String values should be created and appended using two parameters in the
     stdarg fields, that of the string itself, and its length in bytes
     immediately after the string.  A value of -1 may be used if the string
     length is not known.

EXAMPLES
     The follow code fragment will make a JSON object out of the string
     ``Hello <USERNAME>\n'' in the buffer called ``buf'' where ``USERNAME'' is
     the name of the user taken from the runtime environment.  The encoded
     text will be in an allocated buffer called ``s''

           mj_t atom;
           char buf[BUFSIZ];
           char *s;
           int cc;

           (void) memset(&atom, 0x0, sizeof(atom));
           cc = snprintf(buf, sizeof(buf), "Hello %s\n", getenv("USER"));
           mj_create(&atom, "string", buf, cc);
           cc = mj_asprint(&s, &atom, MJ_JSON_ENCODE);

     and the following example will take the (binary) text which has been
     encoded into JSON and is in the buffer ``buf'', such as in the previous
     example, and re-create the original text:

           int from, to, tok, cc;
           char *s;
           mj_t atom;

           (void) memset(&atom, 0x0, sizeof(atom));
           from = to = tok = 0;
           mj_parse(&atom, buf, &from, &to, &tok);
           cc = mj_asprint(&s, &atom, MJ_HUMAN);
           printf("%.*s", cc, s);

     The s pointer points to allocated storage with the original NUL-
     terminated string in it.

SEE ALSO
     calloc(3), free(3)

     ECMA-262: ECMAScript Language Specification, Ecma International, December
     2009, 5th Edition,
     http://www.ecma-international.org/publications/files/ecma-st/ECMA-262.pdf.

HISTORY
     The libmj library first appeared in NetBSD 6.0.

AUTHORS
     Alistair Crooks <agcATNetBSD.org> wrote this implementation and manual
     page.

NetBSD 6.1.5                     June 22, 2011                    NetBSD 6.1.5