c/tsoding.frozen @ 6beb4a628e79d2761bd1921c9c508e65121cc4f7

title: json_walk()

/* JSON token type */
enum json_token_type {
  JSON_TYPE_INVALID = 0, /* memsetting to 0 should create INVALID value */
  JSON_TYPE_STRING,
  JSON_TYPE_NUMBER,
  JSON_TYPE_TRUE,
  JSON_TYPE_FALSE,
  JSON_TYPE_NULL,
  JSON_TYPE_OBJECT_START,
  JSON_TYPE_OBJECT_END,
  JSON_TYPE_ARRAY_START,
  JSON_TYPE_ARRAY_END,

  JSON_TYPES_CNT,
};

/*
 * Structure containing token type and value. Used in `json_walk()` and
 * `json_scanf()` with the format specifier `%T`.
 */
struct json_token {
  const char *ptr;           /* Points to the beginning of the value */
  int len;                   /* Value length */
  enum json_token_type type; /* Type of the token, possible values are above */
};

/* Callback-based API */
typedef void (*json_walk_callback_t)(void *callback_data,
                                     const char *name, size_t name_len,
                                     const char *path,
                                     const struct json_token *token);

/*
 * Parse `json_string`, invoking `callback` in a way similar to SAX parsers;
 * see `json_walk_callback_t`.
 */
int json_walk(const char *json_string, int json_string_length,
              json_walk_callback_t callback, void *callback_data);

json_walk() is a low-level, callback based parsing API. json_walk() calls given callback function for each scanned value.

Callback receives a name, a path to the value, a JSON token that points to the value, and arbitrary user data pointer.

The path is constructed using this rule:

Root element has "" (empty string) path
When an object starts, . (dot) is appended to the path
When an object key is parsed, a key name is appended to the path
When an array is parsed, for each element an [ELEMENT_INDEX] is appended

For example, consider the following json string: { "foo": 123, "bar": [ 1, 2, { "baz": true } ] }. The sequence of callback invocations will be as follows:

type: JSON_TYPE_OBJECT_START, name: NULL, path: "", value: NULL
type: JSON_TYPE_NUMBER, name: "foo", path: ".foo", value: "123"
type: JSON_TYPE_ARRAY_START, name: "bar", path: ".bar", value: NULL
type: JSON_TYPE_NUMBER, name: "0", path: ".bar[0]", value: "1"
type: JSON_TYPE_NUMBER, name: "1", path: ".bar[1]", value: "2"
type: JSON_TYPE_OBJECT_START, name: "2", path: ".bar[2]", value: NULL
type: JSON_TYPE_TRUE, name: "baz", path: ".bar[2].baz", value: "true"
type: JSON_TYPE_OBJECT_END, name: NULL, path: ".bar[2]", value: "{ \"baz\": true }"
type: JSON_TYPE_ARRAY_END, name: NULL, path: ".bar", value: "[ 1, 2, { \"baz\": true } ]"
type: JSON_TYPE_OBJECT_END, name: NULL, path: "", value: "{ \"foo\": 123, \"bar\": [ 1, 2, { \"baz\": true } ] }"

If top-level element is an array: [1, {"foo": 2}]

type: JSON_TYPE_ARRAY_START, name: NULL, path: "", value: NULL
type: JSON_TYPE_NUMBER, name: "0", path: "[0]", value: "1"
type: JSON_TYPE_OBJECT_START, name: "1", path: "[1]", value: NULL
type: JSON_TYPE_NUMBER, name: "foo", path: "[1].foo", value: "2"
type: JSON_TYPE_OBJECT_END, name: NULL, path: "[1]", value: "{\"foo\": 2}"
type: JSON_TYPE_ARRAY_END, name: NULL, path: "", value: "[1, {"foo": 2}]"

If top-level element is an scalar: true

type: JSON_TYPE_TRUE, name: NULL, path: "", value: "true"

json_walk.md 3.3 KB History Raw

title: json_walk()

json_walk.md 3.3 KB

History Raw