sd-json — APIs for Dealing with JSON Objects
#include <systemd/sd-json.h>
pkg-config --cflags --libs libsystemd
sd-json.h is part of
libsystemd(3) and
provides APIs to parse, generate, format and otherwise operate with JSON objects.
The API's central data structure is JsonVariant which encapsulates a JSON object, array, string, boolean, number or null value. These data structures are mostly considered immutable after construction (i.e. their contents won't change, but some meta-data might, such as reference counters).
The APIs broadly fall into five categories:
APIs to directly operate with JsonVariant objects, in the
sd_json_variant* namespace.
APIs to construct complex JSON objects, in the sd_json_build*
namespace.
APIs to map JsonVariant objects and their fields to matching fields in C
structures, in the sd_json_dispatch* namespace.
APIs to convert a string representation of a JSON object into a
JsonVariant object, in the sd_json_parse*
namespace.
APIs to convert an JsonVariant object into its string representation, in
the sd_json_format* namespace.
This JSON library will internally encode JSON integer numbers in the range
INT64_MIN…UINT64_MAX into native 64bit signed or unsigned
integers, and will reproduce them without loss of precision. Non-integer numbers are stored in 64bit IEEE
floating point numbers.
If the functions return string arrays, these are generally
NULL terminated and need to be freed by the
caller with the libc
free(3)
call after use, including the strings referenced therein.
Similarly, individual strings returned need to be freed, as
well.
As a special exception, instead of an empty string array NULL may be returned,
which should be treated equivalent to an empty string array.
Functions described here are available as a shared
library, which can be compiled against and linked to with the
libsystemd pkg-config(1)
file.
The code described here uses
getenv(3),
which is declared to be not multi-thread-safe. This means that the code calling the functions described
here must not call
setenv(3)
from a parallel thread. It is recommended to only do calls to setenv()
from an early phase of the program when no other threads have been started.