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nlohmann::basic_json::patch_inplace

void patch_inplace(const basic_json& json_patch) const;

JSON Patch defines a JSON document structure for expressing a sequence of operations to apply to a JSON document. With this function, a JSON Patch is applied to the current JSON value by executing all operations from the patch. This function applies a JSON patch in place and returns void.

Parameters

json_patch (in)
JSON patch document

Exception safety

No guarantees, value may be corrupted by an unsuccessful patch operation.

Exceptions

  • Throws parse_error.104 if the JSON patch does not consist of an array of objects.
  • Throws parse_error.105 if the JSON patch is malformed (e.g., mandatory attributes are missing); example: "operation add must have member path".
  • Throws out_of_range.401 if an array index is out of range.
  • Throws out_of_range.403 if a JSON pointer inside the patch could not be resolved successfully in the current JSON value; example: "key baz not found".
  • Throws out_of_range.405 if JSON pointer has no parent ("add", "remove", "move")
  • Throws out_of_range.501 if "test" operation was unsuccessful.

Complexity

Linear in the size of the JSON value and the length of the JSON patch. As usually only a fraction of the JSON value is affected by the patch, the complexity can usually be neglected.

Notes

Unlike patch, patch_inplace applies the operation "in place" and no copy of the JSON value is created. That makes it faster for large documents by avoiding the copy. However, the JSON value might be corrupted if the function throws an exception.

Examples

Example

The following code shows how a JSON patch is applied to a value.

#include <iostream>
#include <iomanip>
#include <nlohmann/json.hpp>

using json = nlohmann::json;
using namespace nlohmann::literals;

int main()
{
    // the original document
    json doc = R"(
        {
          "baz": "qux",
          "foo": "bar"
        }
    )"_json;

    // the patch
    json patch = R"(
        [
          { "op": "replace", "path": "/baz", "value": "boo" },
          { "op": "add", "path": "/hello", "value": ["world"] },
          { "op": "remove", "path": "/foo"}
        ]
    )"_json;

    // output original document
    std::cout << "Before\n" << std::setw(4) << doc << std::endl;

    // apply the patch
    doc.patch_inplace(patch);

    // output patched document
    std::cout << "\nAfter\n" << std::setw(4) << doc << std::endl;
}

Output:

Before
{
    "baz": "qux",
    "foo": "bar"
}

After
{
    "baz": "boo",
    "hello": [
        "world"
    ]
}

See also

Version history

  • Added in version 3.11.0.

Last update: August 12, 2022