nlohmann::basic_json::diff¶

staticbasic_jsondiff(constbasic_json&source,
constbasic_json&target);

Creates a JSON Patch so that value source can be changed into the value target by calling patch function.

For two JSON values source and target, the following code yields always true:

source.patch(diff(source,target))==target;

Parameters¶

source (in): JSON value to compare from
target (in): JSON value to compare against

Return value¶

a JSON patch to convert the source to target

Exception safety¶

Strong guarantee: if an exception is thrown, there are no changes in the JSON value.

Complexity¶

Linear in the lengths of source and target.

Notes¶

Currently, only remove, add, and replace operations are generated.

Examples¶

Example

The following code shows how a JSON patch is created as a diff for two JSON values.

#include<iostream>
#include<iomanip>
#include<nlohmann/json.hpp>
usingjson=nlohmann::json;
usingnamespacenlohmann::literals;
intmain()
{
// the source document
jsonsource=R"(
 {
 "baz": "qux",
 "foo": "bar"
 }
)"_json;
// the target document
jsontarget=R"(
 {
 "baz": "boo",
 "hello": [
 "world"
 ]
 }
)"_json;
// create the patch
jsonpatch=json::diff(source,target);
// roundtrip
jsonpatched_source=source.patch(patch);
// output patch and roundtrip result
std::cout<<std::setw(4)<<patch<<"\n\n"
<<std::setw(4)<<patched_source<<std::endl;
}

Output:

[
{
"op":"replace",
"path":"/baz",
"value":"boo"
},
{
"op":"remove",
"path":"/foo"
},
{
"op":"add",
"path":"/hello",
"value":[
"world"
]
}
]
{
"baz":"boo",
"hello":[
"world"
]
}

Version history¶

Added in version 2.0.0.