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sd-json(3) — Linux manual page

SD-JSON(3)                       sd-jsonSD-JSON(3)

NAME        top

       sd-json - APIs for Dealing with JSON Objects

SYNOPSIS        top

#include <systemd/sd-json.h>pkg-config --cflags --libs libsystemd

DESCRIPTION        top

       sd-json.h is part oflibsystemd(3) and provides APIs to parse,       generate, format and otherwise operate with JSON objects.       The API's central data structure isJsonVariantwhich encapsulates       a JSON object, array, string, boolean, number or null value. These       data structures are mostly considered immutable after construction       (i.e. their contents will not change, but some meta-data might,       such as reference counters).       The APIs broadly fall into five categories:       •   APIs to directly operate withJsonVariantobjects, in thesd_json_variant*namespace.       •   APIs to construct complex JSON objects, in thesd_json_build*           namespace.       •   APIs to mapJsonVariantobjects and their fields to matching           fields in C structures, in thesd_json_dispatch*namespace.       •   APIs to convert a string representation of a JSON object into           aJsonVariantobject, in thesd_json_parse*namespace.       •   APIs to convert anJsonVariantobject into its string           representation, in thesd_json_format*namespace.       This JSON library will internally encode JSON integer numbers in       the rangeINT64_MIN...UINT64_MAXinto 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 generallyNULL       terminated and need to be freed by the caller with the libcfree(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 arrayNULLmay       be returned, which should be treated equivalent to an empty string       array.

NOTES        top

       Functions described here are available as a shared library, which       can be compiled against and linked to with thelibsystemd pkg-config(1) file.       The code described here usesgetenv(3), which is declared to be       not multi-thread-safe. This means that the code calling the       functions described here must not callsetenv(3) from a parallel       thread. It is recommended to only do calls tosetenv()from an       early phase of the program when no other threads have been       started.

SEE ALSO        top

systemd(1),sd-varlink(3),pkg-config(1)

COLOPHON        top

       This page is part of thesystemd (systemd system and service       manager) project.  Information about the project can be found at       ⟨http://www.freedesktop.org/wiki/Software/systemd⟩.  If you have a       bug report for this manual page, see       ⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.       This page was obtained from the project's upstream Git repository       ⟨https://github.com/systemd/systemd.git⟩ on 2025-08-11.  (At that       time, the date of the most recent commit that was found in the       repository was 2025-08-11.)  If you discover any rendering       problems in this HTML version of the page, or you believe there is       a better or more up-to-date source for the page, or you have       corrections or improvements to the information in this COLOPHON       (which isnot part of the original manual page), send a mail to       man-pages@man7.orgsystemd 258~rc2SD-JSON(3)

Pages that refer to this page:libsystemd(3), sd_bus_message_dump(3), sd-varlink(3), systemd.directives(7), systemd.index(7)

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