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JsonLib

JsonLib is a public-domain C library that makes converting C structures to and from JSON easy. You describe your struct once with a declarative mapping table, and the library handles marshalling (struct to JSON) and unmarshalling (JSON to struct) in both directions.

The library can parse JSON5, or run in strict JSON mode, and can output either JSON or JSON5. By default it parses JSON5 and outputs JSON, which is the most compatible combination.

Features

  • Marshal C structures to JSON, and unmarshal JSON back into C structures.
  • Parse JSON5 or strict JSON; output JSON or JSON5 with control over indenting, ASCII escaping, bare keywords, single quotes, trailing commas, and hex numbers.
  • Field types: strings, sub-structs, signed and unsigned integers (8/16/32/64-bit), hex integers, floats and doubles, bools, and Base64-encoded binary blobs — each available as a single value, an allocated array, or a fixed-size array.
  • No external dependencies. Builds with CMake.
  • Released into the public domain under the Unlicense.

Quick example

Given a struct and a mapping table:

typedef struct
{
    bool        BoolField;
    char*       StringField;
    uint64_t    U64Field;
} MyStruct;

JlMarshallElement myStructMappings[] =
{
    JlMarshallBool( MyStruct, BoolField, "bool" ),
    JlMarshallString( MyStruct, StringField, "str" ),
    JlMarshallUnsigned( MyStruct, U64Field, "num" )
};

parse this JSON into the struct:

{
    "bool": true,
    "str": "a string",
    "num": 1234
}

MyStruct myStruct = {0};
size_t errorAtPos = 0;

JL_STATUS status = JlJsonToStruct(
    jsonString,
    myStructMappings, sizeof(myStructMappings) / sizeof(myStructMappings[0]),
    &myStruct, &errorAtPos );

Only JsonLib.h needs to be included to use the library.

See the Functions page for the full API, and the Marshalling Reference for every mapping macro.

Building

JsonLib builds with CMake. From the repository root:

make build      # configure and compile everything
make test       # build and run the unit tests
make help       # list all targets

Or drive CMake directly:

cmake -B Build
cmake --build Build

The library builds to a static library (libJsonLib.a); the repository also builds a unit-test suite, a JsonRewrite command-line tool, and a minimal sample program.