JSON Pointer¶

Introduction¶

The library supports JSON Pointer (RFC 6901) as an alternative means to address structured values. A JSON Pointer is a string that identifies a specific value within a JSON document.

Consider the following JSON document

{
"array":["A","B","C"],
"nested":{
"one":1,
"two":2,
"three":[true,false]
}
}

Then every value inside the JSON document can be identified as follows:

Note / does not identify the root (i.e., the whole document), but an object entry with empty key "". See RFC 6901 for more information.

JSON Pointer creation¶

JSON Pointers can be created from a string:

json::json_pointerp("/nested/one");

Furthermore, a user-defined string literal can be used to achieve the same result:

autop="/nested/one"_json_pointer;

The escaping rules of RFC 6901 are implemented. See the constructor documentation for more information.

Value access¶

JSON Pointers can be used in the at, operator[], and value functions just like object keys or array indices.

// the JSON value from above
autoj=json::parse(R"({
 "array": ["A", "B", "C"],
 "nested": {
 "one": 1,
 "two": 2,
 "three": [true, false]
 }
})");
// access values
autoval=j[""_json_pointer];// {"array":["A","B","C"],...}
autoval1=j["/nested/one"_json_pointer];// 1
autoval2=j.at(json::json_pointer("/nested/three/1"));// false
autoval3=j.value(json::json_pointer("/nested/four"),0);// 0

Flatten / unflatten¶

The library implements a function flatten to convert any JSON document into a JSON object where each key is a JSON Pointer and each value is a primitive JSON value (i.e., a string, boolean, number, or null).

// the JSON value from above
autoj=json::parse(R"({
 "array": ["A", "B", "C"],
 "nested": {
 "one": 1,
 "two": 2,
 "three": [true, false]
 }
})");
// create flattened value
autoj_flat=j.flatten();

The resulting value j_flat is:

{
"/array/0":"A",
"/array/1":"B",
"/array/2":"C",
"/nested/one":1,
"/nested/two":2,
"/nested/three/0":true,
"/nested/three/1":false
}

The reverse function, unflatten recreates the original value.

autoj_original=j_flat.unflatten();

See also¶

• Class json_pointer
• Function flatten
• Function unflatten
• JSON Patch