Keil提供的JSON库的使用参数说明--APIReference—Jansson2_keil提示没有jansson

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Docs » API Reference

API Reference

Preliminaries

All declara ons are in

jansson.h

, so it’s enough to

#include <jansson.h>

in each source file.

All constants are prefixed with

JSON_

(except for those describing the library version, prefixed with

JANSSON_

). Other iden fiers are prefixed with

json_

. Type names are suffixed with

and

typedef

‘d

so that the

struct

keyword need not be used.

Library Version

The Jansson version is of the form A.B.C, where A is the major version, B is the minor version and C

is the micro version. If the micro version is zero, it’s omi ed from the version string, i.e. the version

string is just A.B.

When a new release only fixes bugs and doesn’t add new features or func onality, the micro version

is incremented. When new features are added in a backwards compa ble way, the minor version is

incremented and the micro version is set to zero. When there are backwards incompa ble changes,

the major version is incremented and others are set to zero.

The following preprocessor constants specify the current version of the library:

JANSSON_MAJOR_VERSION , JANSSON_MINOR_VERSION , JANSSON_MICRO_VERSION

Integers specifying the major, minor and micro versions, respec vely.

JANSSON_VERSION

A string representa on of the current version, e.g.

"1.2.1"

"1.3"

JANSSON_VERSION_HEX

A 3-byte hexadecimal representa on of the version, e.g.

0x010201

for version 1.2.1 and 0x010300

for version 1.3. This is useful in numeric comparisons, e.g.:

#if JANSSON_VERSION_HEX >= 0x010300

/* Code specific to version 1.3 and above */ #endif

reference count. These func ons 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 json_incref() . As soon as the

value is no longer needed,

json_decref()

should be called to

release the reference.

Normally, all func ons accep ng a JSON value as an argument will manage the reference, i.e. increase

and decrease the reference count as needed. However, some func ons steal the reference, i.e. they

have the same result as if the user called

json_decref()

on the argument right a er calling the func on.

These func ons 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

json_decref()

By using a reference stealing func on json_array_append_new() instead of 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

json_array_append_new() steals the reference when appending the value to the array.

In the following sec ons it is clearly documented whether a func on 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

json_object_set()

(and all the other such func ons 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);

剩余28页未读，继续阅读

张子楠Aaron

2018-06-29

和官方的一样....有些浪费了

HnaLin

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