jansson的使用

https://jansson.readthedocs.org/en/2.5/gettingstarted.html

https://github.com/akheron/jansson/blob/master/win32/vs2010/jansson.vcxproj

./configure
make
make check
make install

/* Create the JSON integer 42 */
json_pack("i", 42);

/* Create the JSON array ["foo", "bar", true] */
json_pack("[ssb]", "foo", "bar", 1);

json_t *json_pack(const char *fmt, ...)

Return value: New reference.

Build a new JSON value according to the format string fmt. For each format character (except for {}[]n), one argument is consumed and used to build the corresponding value. Returns NULL on error.

json_t *json_pack_ex(json_error_t *error, size_t flags, const char *fmt, ...)¶

json_t *json_vpack_ex(json_error_t *error, size_t flags, const char *fmt, va_list ap)

Return value: New reference.

Like json_pack(), but an in the case of an error, an error message is written to error, if it’s not NULL. The flags parameter is currently unused and should be set to 0.

/* Build an empty JSON object */
json_pack("{}");

/* Build the JSON object {"foo": 42, "bar": 7} */
json_pack("{sisi}", "foo", 42, "bar", 7);

/* Like above, ':', ',' and whitespace are ignored */
json_pack("{s:i, s:i}", "foo", 42, "bar", 7);

/* Build the JSON array [[1, 2], {"cool": true}] */
json_pack("[[i,i],{s:b]]", 1, 2, "cool", 1);

enum json_type

The type of a JSON value. The following members are defined:

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 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.

int json_typeof(const json_t *json)

Return the type of the JSON value (a json_type cast to int). json MUST NOT be NULL. This function is actually implemented as a macro for speed.

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_real(const json_t *json)

json_is_true(const json_t *json)

json_is_false(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 and for NULL.

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.

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.

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.

static void test_array_foreach()
{
    size_t index;
    json_t *array1, *array2, *value;
    const char *pcValue=NULL;

array1 = json_pack("[sisisi]", "foo", 1, "bar", 2, "baz", 3);
    array2 = json_array();

json_array_foreach(array1, index, value) {
        pcValue=json_string_value(value);
        if(NULL!=pcValue)
        {
            printf("array1[%d]=%s\n",index,pcValue);
        }
        pcValue=NULL;
        json_array_append(array2, value);
    }
    
    if(!json_equal(array1, array2))
        fail("json_array_foreach failed to iterate all elements");

json_decref(array1);
    json_decref(array2);
}

输出：

array1[0]=foo
array1[2]=bar
array1[4]=baz

int json_unpack(json_t *root, const char *fmt, ...)

Validate and unpack the JSON value root according to the format string fmt. Returns 0 on success and -1 on failure.

int json_unpack_ex(json_t *root, json_error_t *error, size_t flags, const char *fmt, ...)

int json_vunpack_ex(json_t *root, json_error_t *error, size_t flags, const char *fmt, va_list ap)

Validate and unpack the JSON value root according to the format string fmt. If an error occurs and error is not NULL, write error information to error. flags can be used to control the behaviour of the unpacker, see below for the flags. Returns 0 on success and -1 on failure.

The following unpacking flags are available:

JSON_STRICT

Enable the extra validation step checking that all object and array items are unpacked. This is equivalent to appending the format character ! to the end of every array and object in the format string.

JSON_VALIDATE_ONLY

Don’t extract any data, just validate the JSON value against the given format string. Note that object keys must still be specified after the format string.

/* root is the JSON integer 42 */
int myint;
json_unpack(root, "i", &myint);
assert(myint == 42);

/* root is the JSON object {"foo": "bar", "quux": true} */
const char *str;
int boolean;
json_unpack(root, "{s:s, s:b}", "foo", &str, "quux", &boolean);
assert(strcmp(str, "bar") == 0 && boolean == 1);

/* root is the JSON array [[1, 2], {"baz": null} */
json_error_t error;
json_unpack_ex(root, &error, JSON_VALIDATE_ONLY, "[[i,i], {s:n}]", "baz");
/* returns 0 for validation success, nothing is extracted */

/* root is the JSON array [1, 2, 3, 4, 5] */
int myint1, myint2;
json_unpack(root, "[ii!]", &myint1, &myint2);
/* returns -1 for failed validation */

/* root is an empty JSON object */
int myint = 0, myint2 = 0;
json_unpack(root, "{s?i, s?[ii]}",
            "foo", &myint1,
            "bar", &myint2, &myint3);
/* myint1, myint2 or myint3 is no touched as "foo" and "bar" don't exist */

static void test_deep_copy_object(void)
{
    const char *json_object_text =
        "{\"foo\": \"bar\", \"a\": 1, \"b\": 3.141592, \"c\": [1,2,3,4]}";

    json_t *object, *copy;
    void *iter;

    object = json_loads(json_object_text, 0, NULL);
    if(!object)
        fail("unable to parse an object");

    copy = json_deep_copy(object);
    if(!copy)
        fail("unable to deep copy an object");
    if(copy == object)
        fail("deep copying an object doesn't copy");
    if(!json_equal(copy, object))
        fail("deep copying an object produces an inequal copy");

    iter = json_object_iter(object);
    while(iter)
    {   
        const char *key;
        json_t *value1, *value2;

        key = json_object_iter_key(iter);
        value1 = json_object_iter_value(iter);
        value2 = json_object_get(copy, key);

        if(value1 == value2)
            fail("deep copying an object doesn't copy its items");

        iter = json_object_iter_next(object, iter);
    }   

    json_decref(object);
    json_decref(copy);
}

int json_unpack(json_t *root, const char *fmt, ...)

Validate and unpack the JSON value root according to the format string fmt. Returns 0 on success and -1 on failure.

int json_unpack_ex(json_t *root, json_error_t *error, size_t flags, const char *fmt, ...)

int json_vunpack_ex(json_t *root, json_error_t *error, size_t flags, const char *fmt, va_list ap)

Validate and unpack the JSON value root according to the format string fmt. If an error occurs and error is not NULL, write error information to error. flags can be used to control the behaviour of the unpacker, see below for the flags. Returns 0 on success and -1 on failure.

JSON_STRICT

Enable the extra validation step checking that all object and array items are unpacked. This is equivalent to appending the format character ! to the end of every array and object in the format string.

JSON_VALIDATE_ONLY

Don’t extract any data, just validate the JSON value against the given format string. Note that object keys must still be specified after the format string.

/* root is the JSON integer 42 */
int myint;
json_unpack(root, "i", &myint);
assert(myint == 42);

/* root is the JSON object {"foo": "bar", "quux": true} */
const char *str;
int boolean;
json_unpack(root, "{s:s, s:b}", "foo", &str, "quux", &boolean);
assert(strcmp(str, "bar") == 0 && boolean == 1);

/* root is the JSON array [[1, 2], {"baz": null} */
json_error_t error;
json_unpack_ex(root, &error, JSON_VALIDATE_ONLY, "[[i,i], {s:n}]", "baz");
/* returns 0 for validation success, nothing is extracted */

/* root is the JSON array [1, 2, 3, 4, 5] */
int myint1, myint2;
json_unpack(root, "[ii!]", &myint1, &myint2);
/* returns -1 for failed validation */

/* root is an empty JSON object */
int myint = 0, myint2 = 0;
json_unpack(root, "{s?i, s?[ii]}",
            "foo", &myint1,
            "bar", &myint2, &myint3);
/* myint1, myint2 or myint3 is no touched as "foo" and "bar" don't exist */

    /* string */
    j = json_string("foo");
    rv = json_unpack(j, "s", &s);
    if(rv || strcmp(s, "foo"))
        fail("json_unpack string failed");
    json_decref(j);

    /* empty object */
    j = json_object();
    if(json_unpack(j, "{}"))
        fail("json_unpack empty object failed");
    json_decref(j);

    /* empty list */
    j = json_array();
    if(json_unpack(j, "[]"))
        fail("json_unpack empty list failed");
    json_decref(j);

    /* non-incref'd object */
    j = json_object();
    rv = json_unpack(j, "o", &j2);
    if(j2 != j || j->refcount != 1)
        fail("json_unpack object failed");
    json_decref(j);

    /* incref'd object */
    j = json_object();
    rv = json_unpack(j, "O", &j2);
    if(j2 != j || j->refcount != 2)
        fail("json_unpack object failed");
    json_decref(j);
    json_decref(j);

    /* simple object */
    j = json_pack("{s:i}", "foo", 42);
    rv = json_unpack(j, "{s:i}", "foo", &i1);
    if(rv || i1 != 42) 
        fail("json_unpack simple object failed");
    json_decref(j);

    /* simple array */
    j = json_pack("[iii]", 1, 2, 3); 
    rv = json_unpack(j, "[i,i,i]", &i1, &i2, &i3);
    if(rv || i1 != 1 || i2 != 2 || i3 != 3)
        fail("json_unpack simple array failed");
    json_decref(j);

By default, Jansson uses malloc() and free() for memory allocation. These functions can be overridden if custom behavior is needed.

json_malloc_t

A typedef for a function pointer with malloc()‘s signature:

typedef void *(*json_malloc_t)(size_t);

json_free_t

A typedef for a function pointer with free()‘s signature:

typedef void (*json_free_t)(void *);

void json_set_alloc_funcs(json_malloc_t malloc_fn, json_free_t free_fn)

Use malloc_fn instead of malloc() and free_fn instead of free(). This function has to be called before any other Jansson’s API functions to ensure that all memory operations use the same functions.

Examples:

Use the Boehm’s conservative garbage collector for memory operations:

json_set_alloc_funcs(GC_malloc, GC_free);

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.

int json_object_update_existing(json_t *object, json_t *other)

Like json_object_update(), but only the values of existing keys are updated. No new keys are created. Returns 0 on success or -1 on error.

New in version 2.3.

int json_object_update_missing(json_t *object, json_t *other)

Like json_object_update(), but only new keys are created. The value of any existing key is not changed. Returns 0 on success or -1 on error.