+.. _apiref:
+
*************
API Reference
*************
also dynamic in nature. There's one C type to represent all JSON
values, and this structure knows the type of the JSON value it holds.
-.. ctype:: json_t
+.. type:: json_t
This data structure is used throughout the library to represent all
JSON values. It always contains the type of the JSON value it holds
and the value's reference count. The rest depends on the type of the
value.
-Objects of :ctype:`json_t` are always used through a pointer. There
+Objects of :type:`json_t` are always used through a pointer. There
are APIs for querying the type, manipulating the reference count, and
for constructing and manipulating values of different types.
+Unless noted otherwise, all API functions return an error value if an
+error occurs. Depending on the function's signature, the error value
+is either *NULL* or -1. Invalid arguments or invalid input are
+apparent sources for errors. Memory allocation and I/O operations may
+also cause errors.
+
Type
----
The type of a JSON value is queried and tested using the following
functions:
-.. ctype:: enum json_type
+.. type:: enum json_type
The type of a JSON value. The following members are defined:
- +-------------------------+
- | :const:`JSON_OBJECT` |
- +-------------------------+
- | :const:`JSON_ARRAY` |
- +-------------------------+
- | :const:`JSON_STRING` |
- +-------------------------+
- | :const:`JSON_INTEGER` |
- +-------------------------+
- | :const:`JSON_REAL` |
- +-------------------------+
- | :const:`JSON_TRUE` |
- +-------------------------+
- | :const:`JSON_FALSE` |
- +-------------------------+
- | :const:`JSON_NULL` |
- +-------------------------+
+ +--------------------+
+ | ``JSON_OBJECT`` |
+ +--------------------+
+ | ``JSON_ARRAY`` |
+ +--------------------+
+ | ``JSON_STRING`` |
+ +--------------------+
+ | ``JSON_INTEGER`` |
+ +--------------------+
+ | ``JSON_REAL`` |
+ +--------------------+
+ | ``JSON_TRUE`` |
+ +--------------------+
+ | ``JSON_FALSE`` |
+ +--------------------+
+ | ``JSON_NULL`` |
+ +--------------------+
These correspond to JSON object, array, string, number, boolean and
null. A number is represented by either a value of the type
- :const:`JSON_INTEGER` or of the type :const:`JSON_REAL`. A true
- boolean value is represented by a value of the type
- :const:`JSON_TRUE` and false by a value of the type
- :const:`JSON_FALSE`.
+ ``JSON_INTEGER`` or of the type ``JSON_REAL``. A true boolean value
+ is represented by a value of the type ``JSON_TRUE`` and false by a
+ value of the type ``JSON_FALSE``.
-.. cfunction:: int json_typeof(const json_t *json)
+.. function:: int json_typeof(const json_t *json)
- Return the type of the JSON value (a :ctype:`json_type` cast to
- :ctype:`int`). This function is actually implemented as a macro for
- speed.
+ Return the type of the JSON value (a :type:`json_type` cast to
+ :type:`int`). *json* MUST NOT be *NULL*. This function is actually
+ implemented as a macro for speed.
-.. cfunction:: json_is_object(const json_t *json)
+.. function:: json_is_object(const json_t *json)
json_is_array(const json_t *json)
json_is_string(const json_t *json)
json_is_integer(const json_t *json)
json_is_null(const json_t *json)
These functions (actually macros) return true (non-zero) for values
- of the given type, and false (zero) for values of other types.
+ of the given type, and false (zero) for values of other types and
+ for *NULL*.
+
+.. function:: json_is_number(const json_t *json)
-.. cfunction:: json_is_number(const json_t *json)
+ Returns true for values of types ``JSON_INTEGER`` and
+ ``JSON_REAL``, and false for other types and for *NULL*.
- Returns true for values of types :const:`JSON_INTEGER` and
- :const:`JSON_REAL`, and false for other types.
+.. function:: json_is_boolean(const json_t *json)
-.. cfunction:: json_is_boolean(const json_t *json)
+ Returns true for types ``JSON_TRUE`` and ``JSON_FALSE``, and false
+ for values of other types and for *NULL*.
- Returns true for types :const:`JSON_TRUE` and :const:`JSON_FALSE`,
- and false for values of other types.
+.. _apiref-reference-count:
Reference Count
---------------
The following functions are used to manipulate the reference count.
-.. cfunction:: json_t *json_incref(json_t *json)
+.. function:: json_t *json_incref(json_t *json)
- Increment the reference count of *json*.
+ Increment the reference count of *json* if it's not non-*NULL*.
+ Returns *json*.
-.. cfunction:: void json_decref(json_t *json)
+.. function:: void json_decref(json_t *json)
Decrement the reference count of *json*. As soon as a call to
- :cfunc:`json_decref()` drops the reference count to zero, the value
+ :func:`json_decref()` drops the reference count to zero, the value
is destroyed and it can no longer be used.
Functions creating new JSON values set the reference count to 1. These
returning (existing) JSON values do not normally increase the
reference count. These functions are said to return a **borrowed
reference**. So, if the user will hold a reference to a value returned
-as a borrowed reference, he must call :cfunc:`json_incref`. As soon as
-the value is no longer needed, :cfunc:`json_decref` should be called
+as a borrowed reference, he must call :func:`json_incref`. As soon as
+the value is no longer needed, :func:`json_decref` should be called
to release the reference.
Normally, all functions accepting a JSON value as an argument will
manage the reference, i.e. increase and decrease the reference count
as needed. However, some functions **steal** the reference, i.e. they
-have the same result as if the user called :cfunc:`json_decref()` on
-the argument right after calling the function. These are usually
-convenience functions for adding new references to containers and not
-to worry about the reference count.
+have the same result as if the user called :func:`json_decref()` on
+the argument right after calling the function. These functions are
+suffixed with ``_new`` or have ``_new_`` somewhere in their name.
+
+For example, the following code creates a new JSON array and appends
+an integer to it::
+
+ json_t *array, *integer;
+
+ array = json_array();
+ integer = json_integer(42);
+
+ json_array_append(array, integer);
+ json_decref(integer);
+
+Note how the caller has to release the reference to the integer value
+by calling :func:`json_decref()`. By using a reference stealing
+function :func:`json_array_append_new()` instead of
+:func:`json_array_append()`, the code becomes much simpler::
+
+ json_t *array = json_array();
+ json_array_append_new(array, json_integer(42));
+
+In this case, the user doesn't have to explicitly release the
+reference to the integer value, as :func:`json_array_append_new()`
+steals the reference when appending the value to the array.
In the following sections it is clearly documented whether a function
will return a new or borrowed reference or steal a reference to its
argument.
+Circular References
+-------------------
+
+A circular reference is created when an object or an array is,
+directly or indirectly, inserted inside itself. The direct case is
+simple::
+
+ json_t *obj = json_object();
+ json_object_set(obj, "foo", obj);
+
+Jansson will refuse to do this, and :func:`json_object_set()` (and
+all the other such functions for objects and arrays) will return with
+an error status. The indirect case is the dangerous one::
+
+ json_t *arr1 = json_array(), *arr2 = json_array();
+ json_array_append(arr1, arr2);
+ json_array_append(arr2, arr1);
+
+In this example, the array ``arr2`` is contained in the array
+``arr1``, and vice versa. Jansson cannot check for this kind of
+indirect circular references without a performance hit, so it's up to
+the user to avoid them.
+
+If a circular reference is created, the memory consumed by the values
+cannot be freed by :func:`json_decref()`. The reference counts never
+drops to zero because the values are keeping the references to each
+other. Moreover, trying to encode the values with any of the encoding
+functions will fail. The encoder detects circular references and
+returns an error status.
+
+
True, False and Null
====================
-.. cfunction:: json_t *json_true(void)
+These values are implemented as singletons, so each of these functions
+returns the same value each time.
+
+.. function:: json_t *json_true(void)
.. refcounting:: new
- Returns a value of the type :const:`JSON_TRUE`, or *NULL* on
- error.
+ Returns the JSON true value.
-.. cfunction:: json_t *json_false(void)
+.. function:: json_t *json_false(void)
.. refcounting:: new
- Returns a value of the type :const:`JSON_FALSE`, or *NULL* on
- error.
+ Returns the JSON false value.
-.. cfunction:: json_t *json_null(void)
+.. function:: json_t *json_null(void)
.. refcounting:: new
- Returns a value of the type :const:`JSON_NULL`, or *NULL* on
- error.
+ Returns the JSON null value.
String
======
-.. cfunction:: json_t *json_string(const char *value)
+Jansson uses UTF-8 as the character encoding. All JSON strings must be
+valid UTF-8 (or ASCII, as it's a subset of UTF-8). Normal null
+terminated C strings are used, so JSON strings may not contain
+embedded null characters. All other Unicode codepoints U+0001 through
+U+10FFFF are allowed.
+
+.. function:: json_t *json_string(const char *value)
.. refcounting:: new
- Returns a new value of the type :const:`JSON_STRING`, or *NULL* on
- error. *value* must be a valid UTF-8 encoded Unicode string.
+ Returns a new JSON string, or *NULL* on error. *value* must be a
+ valid UTF-8 encoded Unicode string.
+
+.. function:: json_t *json_string_nocheck(const char *value)
+
+ .. refcounting:: new
-.. cfunction:: const char *json_string_value(const json_t *json)
+ Like :func:`json_string`, but doesn't check that *value* is valid
+ UTF-8. Use this function only if you are certain that this really
+ is the case (e.g. you have already checked it by other means).
- Returns the associated value of a :const:`JSON_STRING` value as a
- null terminated UTF-8 encoded string.
+.. function:: const char *json_string_value(const json_t *string)
+
+ Returns the associated value of *string* as a null terminated UTF-8
+ encoded string, or *NULL* if *string* is not a JSON string.
+
+.. function:: int json_string_set(const json_t *string, const char *value)
+
+ Sets the associated value of *string* to *value*. *value* must be a
+ valid UTF-8 encoded Unicode string. Returns 0 on success and -1 on
+ error.
+
+.. function:: int json_string_set_nocheck(const json_t *string, const char *value)
+
+ Like :func:`json_string_set`, but doesn't check that *value* is
+ valid UTF-8. Use this function only if you are certain that this
+ really is the case (e.g. you have already checked it by other
+ means).
Number
======
-.. cfunction:: json_t *json_integer(int value)
+The JSON specification only contains one numeric type, "number". The C
+programming language has distinct types for integer and floating-point
+numbers, so for practical reasons Jansson also has distinct types for
+the two. They are called "integer" and "real", respectively. For more
+information, see :ref:`rfc-conformance`.
+
+.. type:: json_int_t
+
+ This is the C type that is used to store JSON integer values. It
+ represents the widest integer type available on your system. In
+ practice it's just a typedef of ``long long`` if your compiler
+ supports it, otherwise ``long``.
+
+ Usually, you can safely use plain ``int`` in place of
+ ``json_int_t``, and the implicit C integer conversion handles the
+ rest. Only when you know that you need the full 64-bit range, you
+ should use ``json_int_t`` explicitly.
+
+``JSON_INTEGER_IS_LONG_LONG``
+
+ This is a preprocessor variable that holds the value 1 if
+ :type:`json_int_t` is ``long long``, and 0 if it's ``long``. It
+ can be used as follows::
+
+ #if JSON_INTEGER_IS_LONG_LONG
+ /* Code specific for long long */
+ #else
+ /* Code specific for long */
+ #endif
+
+``JSON_INTEGER_FORMAT``
+
+ This is a macro that expands to a :func:`printf()` conversion
+ specifier that corresponds to :type:`json_int_t`, without the
+ leading ``%`` sign, i.e. either ``"lld"`` or ``"ld"``. This macro
+ is required because the actual type of :type:`json_int_t` can be
+ either ``long`` or ``long long``, and :func:`printf()` reuiqres
+ different length modifiers for the two.
+
+ Example::
+
+ json_int_t x = 123123123;
+ printf("x is %" JSON_INTEGER_FORMAT "\n", x);
+
+
+.. function:: json_t *json_integer(json_int_t value)
.. refcounting:: new
- Returns a new value of the type :const:`JSON_INTEGER`, or *NULL* on
- error.
+ Returns a new JSON integer, or *NULL* on error.
+
+.. function:: json_int_t json_integer_value(const json_t *integer)
+
+ Returns the associated value of *integer*, or 0 if *json* is not a
+ JSON integer.
-.. cfunction:: int json_integer_value(const json_t *json)
+.. function:: int json_integer_set(const json_t *integer, json_int_t value)
- Returns the associated integer value of values of the type
- :const:`JSON_INTEGER`, or 0 for values of other types.
+ Sets the associated value of *integer* to *value*. Returns 0 on
+ success and -1 if *integer* is not a JSON integer.
-.. cfunction:: json_t *json_real(double value)
+.. function:: json_t *json_real(double value)
.. refcounting:: new
- Returns a new value of the type :const:`JSON_REAL`, or *NULL* on
- error.
+ Returns a new JSON real, or *NULL* on error.
+
+.. function:: double json_real_value(const json_t *real)
-.. cfunction:: double json_real_value(const json_t *json)
+ Returns the associated value of *real*, or 0.0 if *real* is not a
+ JSON real.
- Returns the associated real value of values of the type
- :const:`JSON_INTEGER`, or 0 for values of other types.
+.. function:: int json_real_set(const json_t *real, double value)
+
+ Sets the associated value of *real* to *value*. Returns 0 on
+ success and -1 if *real* is not a JSON real.
In addition to the functions above, there's a common query function
for integers and reals:
-.. cfunction:: double json_number_value(const json_t *json)
+.. function:: double json_number_value(const json_t *json)
- Returns the value of either ``JSON_INTEGER`` or ``JSON_REAL``, cast
- to double regardless of the actual type.
+ Returns the associated value of the JSON integer or JSON real
+ *json*, cast to double regardless of the actual type. If *json* is
+ neither JSON real nor JSON integer, 0.0 is returned.
Array
A JSON array is an ordered collection of other JSON values.
-.. cfunction:: json_t *json_array(void)
+.. function:: json_t *json_array(void)
.. refcounting:: new
- Returns a new value of the type :const:`JSON_ARRAY`, or *NULL* on
- error. Initially, the array is empty.
+ Returns a new JSON array, or *NULL* on error. Initially, the array
+ is empty.
-.. cfunction:: unsigned int json_array_size(const json_t *array)
+.. function:: size_t json_array_size(const json_t *array)
- Returns the number of elements in *array*.
+ Returns the number of elements in *array*, or 0 if *array* is NULL
+ or not a JSON array.
-.. cfunction:: json_t *json_array_get(const json_t *array, unsigned int index)
+.. function:: json_t *json_array_get(const json_t *array, size_t index)
.. refcounting:: borrow
- Returns the element in *array* at position *index*, or *NULL* if
- *index* is out of range. The valid range for *index* is from 0 to
- the return value of :cfunc:`json_array_size()` minus 1.
+ Returns the element in *array* at position *index*. The valid range
+ for *index* is from 0 to the return value of
+ :func:`json_array_size()` minus 1. If *array* is not a JSON array,
+ if *array* is *NULL*, or if *index* is out of range, *NULL* is
+ returned.
-.. cfunction:: int json_array_set(json_t *array, unsigned int index, json_t *value)
+.. function:: int json_array_set(json_t *array, size_t index, json_t *value)
Replaces the element in *array* at position *index* with *value*.
- Returns 0 on success, or -1 if *index* is out of range. The valid
- range for *index* is from 0 to the return value of
- :cfunc:`json_array_size()` minus 1.
+ The valid range for *index* is from 0 to the return value of
+ :func:`json_array_size()` minus 1. Returns 0 on success and -1 on
+ error.
-.. cfunction:: int json_array_set_new(json_t *array, unsigned int index, json_t *value)
+.. function:: int json_array_set_new(json_t *array, size_t index, json_t *value)
- Like :cfunc:`json_array_set()` but steals the reference to *value*.
+ Like :func:`json_array_set()` but steals the reference to *value*.
This is useful when *value* is newly created and not used after
the call.
- .. versionadded:: 1.1
-
-.. cfunction:: int json_array_append(json_t *array, json_t *value)
+.. function:: int json_array_append(json_t *array, json_t *value)
Appends *value* to the end of *array*, growing the size of *array*
by 1. Returns 0 on success and -1 on error.
-.. cfunction:: int json_array_append_new(json_t *array, json_t *value)
+.. function:: int json_array_append_new(json_t *array, json_t *value)
+
+ Like :func:`json_array_append()` but steals the reference to
+ *value*. This is useful when *value* is newly created and not used
+ after the call.
+
+.. function:: int json_array_insert(json_t *array, size_t index, json_t *value)
+
+ Inserts *value* to *array* at position *index*, shifting the
+ elements at *index* and after it one position towards the end of
+ the array. Returns 0 on success and -1 on error.
- Like :cfunc:`json_array_append()` but steals the reference to
+.. function:: int json_array_insert_new(json_t *array, size_t index, json_t *value)
+
+ Like :func:`json_array_insert()` but steals the reference to
*value*. This is useful when *value* is newly created and not used
after the call.
- .. versionadded:: 1.1
+.. function:: int json_array_remove(json_t *array, size_t index)
+
+ Removes the element in *array* at position *index*, shifting the
+ elements after *index* one position towards the start of the array.
+ Returns 0 on success and -1 on error.
+
+.. function:: int json_array_clear(json_t *array)
+
+ Removes all elements from *array*. Returns 0 on sucess and -1 on
+ error.
+
+.. function:: int json_array_extend(json_t *array, json_t *other_array)
+
+ Appends all elements in *other_array* to the end of *array*.
+ Returns 0 on success and -1 on error.
Object
A JSON object is a dictionary of key-value pairs, where the key is a
Unicode string and the value is any JSON value.
-.. cfunction:: json_t *json_object(void)
+.. function:: json_t *json_object(void)
.. refcounting:: new
- Returns a new value of the type :const:`JSON_OBJECT`, or *NULL* on
- error. Initially, the object is empty.
+ Returns a new JSON object, or *NULL* on error. Initially, the
+ object is empty.
+
+.. function:: size_t json_object_size(const json_t *object)
-.. cfunction:: json_t *json_object_get(const json_t *object, const char *key)
+ Returns the number of elements in *object*, or 0 if *object* is not
+ a JSON object.
+
+.. function:: json_t *json_object_get(const json_t *object, const char *key)
.. refcounting:: borrow
Get a value corresponding to *key* from *object*. Returns *NULL* if
*key* is not found and on error.
-.. cfunction:: int json_object_set(json_t *object, const char *key, json_t *value)
+.. function:: int json_object_set(json_t *object, const char *key, json_t *value)
Set the value of *key* to *value* in *object*. *key* must be a
- valid terminated UTF-8 encoded Unicode string. If there already is
- a value for *key*, it is replaced by the new value. Returns 0 on
- success and -1 on error.
+ valid null terminated UTF-8 encoded Unicode string. If there
+ already is a value for *key*, it is replaced by the new value.
+ Returns 0 on success and -1 on error.
+
+.. function:: int json_object_set_nocheck(json_t *object, const char *key, json_t *value)
-.. cfunction:: int json_object_set_new(json_t *object, const char *key, json_t *value)
+ Like :func:`json_object_set`, but doesn't check that *key* is
+ valid UTF-8. Use this function only if you are certain that this
+ really is the case (e.g. you have already checked it by other
+ means).
- Like :cfunc:`json_object_set()` but steals the reference to
+.. function:: int json_object_set_new(json_t *object, const char *key, json_t *value)
+
+ Like :func:`json_object_set()` but steals the reference to
*value*. This is useful when *value* is newly created and not used
after the call.
- .. versionadded:: 1.1
+.. function:: int json_object_set_new_nocheck(json_t *object, const char *key, json_t *value)
+
+ Like :func:`json_object_set_new`, but doesn't check that *key* is
+ valid UTF-8. Use this function only if you are certain that this
+ really is the case (e.g. you have already checked it by other
+ means).
-.. cfunction:: int json_object_del(json_t *object, const char *key)
+.. function:: int json_object_del(json_t *object, const char *key)
Delete *key* from *object* if it exists. Returns 0 on success, or
-1 if *key* was not found.
+.. function:: int json_object_clear(json_t *object)
+
+ Remove all elements from *object*. Returns 0 on success and -1 if
+ *object* is not a JSON object.
+
+.. function:: int json_object_update(json_t *object, json_t *other)
+
+ Update *object* with the key-value pairs from *other*, overwriting
+ existing keys. Returns 0 on success or -1 on error.
+
+
The following functions implement an iteration protocol for objects:
-.. cfunction:: void *json_object_iter(json_t *object)
+.. function:: void *json_object_iter(json_t *object)
Returns an opaque iterator which can be used to iterate over all
key-value pairs in *object*, or *NULL* if *object* is empty.
-.. cfunction:: void *json_object_iter_next(json_t *object, void *iter)
+.. function:: void *json_object_iter_at(json_t *object, const char *key)
+
+ Like :func:`json_object_iter()`, but returns an iterator to the
+ key-value pair in *object* whose key is equal to *key*, or NULL if
+ *key* is not found in *object*. Iterating forward to the end of
+ *object* only yields all key-value pairs of the object if *key*
+ happens to be the first key in the underlying hash table.
+
+.. function:: void *json_object_iter_next(json_t *object, void *iter)
Returns an iterator pointing to the next key-value pair in *object*
after *iter*, or *NULL* if the whole object has been iterated
through.
-.. cfunction:: const char *json_object_iter_key(void *iter)
+.. function:: const char *json_object_iter_key(void *iter)
Extract the associated key from *iter*.
-.. cfunction:: json_t *json_object_iter_value(void *iter)
+.. function:: json_t *json_object_iter_value(void *iter)
.. refcounting:: borrow
Extract the associated value from *iter*.
+.. function:: int json_object_iter_set(json_t *object, void *iter, json_t *value)
+
+ Set the value of the key-value pair in *object*, that is pointed to
+ by *iter*, to *value*.
+
+.. function:: int json_object_iter_set_new(json_t *object, void *iter, json_t *value)
+
+ Like :func:`json_object_iter_set()`, but steals the reference to
+ *value*. This is useful when *value* is newly created and not used
+ after the call.
+
+The iteration protocol can be used for example as follows::
+
+ /* obj is a JSON object */
+ const char *key;
+ json_t *value;
+ void *iter = json_object_iter(obj);
+ while(iter)
+ {
+ key = json_object_iter_key(iter);
+ value = json_object_iter_value(iter);
+ /* use key and value ... */
+ iter = json_object_iter_next(obj, iter);
+ }
+
Encoding
========
values to JSON. Only objects and arrays can be encoded, since they are
the only valid "root" values of a JSON text.
+By default, the output has no newlines, and spaces are used between
+array and object elements for a readable output. This behavior can be
+altered by using the ``JSON_INDENT`` and ``JSON_COMPACT`` flags
+described below. A newline is never appended to the end of the encoded
+JSON data.
+
Each function takes a *flags* parameter that controls some aspects of
how the data is encoded. Its default value is 0. The following macros
can be ORed together to obtain *flags*.
``JSON_INDENT(n)``
- Pretty-print the result, indenting arrays and objects by *n*
- spaces. The valid range for *n* is between 0 and 255, other values
- result in an undefined output. If ``JSON_INDENT`` is not used or
- *n* is 0, no pretty-printing is done and the result is a compact
- representation.
+ Pretty-print the result, using newlines between array and object
+ items, and indenting with *n* spaces. The valid range for *n* is
+ between 0 and 32, other values result in an undefined output. If
+ ``JSON_INDENT`` is not used or *n* is 0, no newlines are inserted
+ between array and object items.
+
+``JSON_COMPACT``
+ This flag enables a compact representation, i.e. sets the separator
+ between array and object items to ``","`` and between object keys
+ and values to ``":"``. Without this flag, the corresponding
+ separators are ``", "`` and ``": "`` for more readable output.
+
+``JSON_ENSURE_ASCII``
+ If this flag is used, the output is guaranteed to consist only of
+ ASCII characters. This is achived by escaping all Unicode
+ characters outside the ASCII range.
+
+``JSON_SORT_KEYS``
+ If this flag is used, all the objects in output are sorted by key.
+ This is useful e.g. if two JSON texts are diffed or visually
+ compared.
+
+``JSON_PRESERVE_ORDER``
+ If this flag is used, object keys in the output are sorted into the
+ same order in which they were first inserted to the object. For
+ example, decoding a JSON text and then encoding with this flag
+ preserves the order of object keys.
The following functions perform the actual JSON encoding. The result
is in UTF-8.
-.. cfunction:: char *json_dumps(const json_t *root, uint32_t flags)
+.. function:: char *json_dumps(const json_t *root, size_t flags)
Returns the JSON representation of *root* as a string, or *NULL* on
error. *flags* is described above. The return value must be freed
- by the caller using :cfunc:`free()`.
+ by the caller using :func:`free()`.
-.. cfunction:: int json_dumpf(const json_t *root, FILE *output, uint32_t flags)
+.. function:: int json_dumpf(const json_t *root, FILE *output, size_t flags)
Write the JSON representation of *root* to the stream *output*.
*flags* is described above. Returns 0 on success and -1 on error.
+ If an error occurs, something may have already been written to
+ *output*. In this case, the output is undefined and most likely not
+ valid JSON.
-.. cfunction:: int json_dump_file(const json_t *json, const char *path, uint32_t flags)
+.. function:: int json_dump_file(const json_t *json, const char *path, size_t flags)
Write the JSON representation of *root* to the file *path*. If
*path* already exists, it is overwritten. *flags* is described
text to the Jansson representation of JSON data. The JSON
specification requires that a JSON text is either a serialized array
or object, and this requirement is also enforced with the following
-functions.
+functions. In other words, the top level value in the JSON text being
+decoded must be either array or object.
+
+See :ref:`rfc-conformance` for a discussion on Jansson's conformance
+to the JSON specification. It explains many design decisions that
+affect especially the behavior of the decoder.
+
+.. function:: json_t *json_loads(const char *input, size_t flags, json_error_t *error)
+
+ .. refcounting:: new
+
+ Decodes the JSON string *input* and returns the array or object it
+ contains, or *NULL* on error, in which case *error* is filled with
+ information about the error. See above for discussion on the
+ *error* parameter. *flags* is currently unused, and should be set
+ to 0.
+
+.. function:: json_t *json_loadf(FILE *input, size_t flags, json_error_t *error)
+
+ .. refcounting:: new
+
+ Decodes the JSON text in stream *input* and returns the array or
+ object it contains, or *NULL* on error, in which case *error* is
+ filled with information about the error. See above for discussion
+ on the *error* parameter. *flags* is currently unused, and should
+ be set to 0.
-The only supported character encoding is UTF-8 (which ASCII is a
-subset of).
+.. function:: json_t *json_load_file(const char *path, size_t flags, json_error_t *error)
-.. ctype:: json_error_t
+ .. refcounting:: new
+
+ Decodes the JSON text in file *path* and returns the array or
+ object it contains, or *NULL* on error, in which case *error* is
+ filled with information about the error. See above for discussion
+ on the *error* parameter. *flags* is currently unused, and should
+ be set to 0.
+
+.. type:: json_error_t
This data structure is used to return information on decoding
- errors from the decoding functions. Its definition is repeated
- here::
+ errors from the decoding functions.
+
+ .. member:: const char *text
+
+ The error message (in UTF-8), or an empty string if a message is
+ not available.
+
+ .. member:: int line
- #define JSON_ERROR_TEXT_LENGTH 160
+ The line number on which the error occurred, or -1 if this
+ information is not available.
- typedef struct {
- char text[JSON_ERROR_TEXT_LENGTH];
- int line;
- } json_error_t;
+ .. member:: int column
- *line* is the line number on which the error occurred, or -1 if
- this information is not available. *text* contains the error
- message (in UTF-8), or an empty string if a message is not
- available.
+ The character column on which the error occurred, or -1 if this
+ information is not available.
- The normal usef of :ctype:`json_error_t` is to allocate it normally
- on the stack, and pass a pointer to a decoding function. Example::
+ .. member:: const char *source
+
+ Source of the error. This is (a part of) the file name when
+ using :func:`json_load_file()`, or a special identifier in angle
+ brackets otherwise (e.g. ``<string>``).
+
+ The normal use of :type:`json_error_t` is to allocate it on the
+ stack, and pass a pointer to a decoding function. Example::
int main() {
json_t *json;
json_error_t error;
- json = json_load_file("/path/to/file.json", &error);
+ json = json_load_file("/path/to/file.json", 0, &error);
if(!json) {
/* the error variable contains error information */
}
above example), the contents of ``error`` are unspecified.
All decoding functions also accept *NULL* as the
- :ctype:`json_error_t` pointer, in which case no error information
+ :type:`json_error_t` pointer, in which case no error information
is returned to the caller.
-The following functions perform the actual JSON decoding.
-.. cfunction:: json_t *json_loads(const char *input, json_error_t *error)
+Equality
+========
- .. refcounting:: new
+Testing for equality of two JSON values cannot, in general, be
+achieved using the ``==`` operator. Equality in the terms of the
+``==`` operator states that the two :type:`json_t` pointers point to
+exactly the same JSON value. However, two JSON values can be equal not
+only if they are exactly the same value, but also if they have equal
+"contents":
- Decodes the JSON string *input* and returns the array or object it
- contains, or *NULL* on error, in which case *error* is filled with
- information about the error. See above for discussion on the
- *error* parameter.
+* Two integer or real values are equal if their contained numeric
+ values are equal. An integer value is never equal to a real value,
+ though.
+
+* Two strings are equal if their contained UTF-8 strings are equal,
+ byte by byte. Unicode comparison algorithms are not implemented.
-.. cfunction:: json_t *json_loadf(FILE *input, json_error_t *error)
+* Two arrays are equal if they have the same number of elements and
+ each element in the first array is equal to the corresponding
+ element in the second array.
+
+* Two objects are equal if they have exactly the same keys and the
+ value for each key in the first object is equal to the value of the
+ corresponding key in the second object.
+
+* Two true, false or null values have no "contents", so they are equal
+ if their types are equal. (Because these values are singletons,
+ their equality can actually be tested with ``==``.)
+
+The following function can be used to test whether two JSON values are
+equal.
+
+.. function:: int json_equal(json_t *value1, json_t *value2)
+
+ Returns 1 if *value1* and *value2* are equal, as defined above.
+ Returns 0 if they are inequal or one or both of the pointers are
+ *NULL*.
+
+
+Copying
+=======
+
+Because of reference counting, passing JSON values around doesn't
+require copying them. But sometimes a fresh copy of a JSON value is
+needed. For example, if you need to modify an array, but still want to
+use the original afterwards, you should take a copy of it first.
+
+Jansson supports two kinds of copying: shallow and deep. There is a
+difference between these methods only for arrays and objects. Shallow
+copying only copies the first level value (array or object) and uses
+the same child values in the copied value. Deep copying makes a fresh
+copy of the child values, too. Moreover, all the child values are deep
+copied in a recursive fashion.
+
+.. function:: json_t *json_copy(json_t *value)
.. refcounting:: new
- Decodes the JSON text in stream *input* and returns the array or
- object it contains, or *NULL* on error, in which case *error* is
- filled with information about the error. See above for discussion
- on the *error* parameter.
+ Returns a shallow copy of *value*, or *NULL* on error.
-.. cfunction:: json_t *json_load_file(const char *path, json_error_t *error)
+.. function:: json_t *json_deep_copy(json_t *value)
.. refcounting:: new
- Decodes the JSON text in file *path* and returns the array or
- object it contains, or *NULL* on error, in which case *error* is
- filled with information about the error. See above for discussion
- on the *error* parameter.
+ Returns a deep copy of *value*, or *NULL* on error.
projects / jansson.git / blobdiff