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### jsonpointer extension
[JSON Pointer](https://tools.ietf.org/html/rfc6901) defines a string syntax to locate a specific value in a JSON document.
A JSON Pointer is a string of zero or more tokens, each token prefixed by `/` characters.
These tokens denote keys in JSON objects or indexes in JSON arrays. An empty string with zero tokens points
to the root of a json document.
The characters `~` and `/` have special meanings in JSON Pointer,
so if a key in a JSON object has these characters, `~` needs to be escaped as `~0`,
and `/` needs to be escaped as `~1`.
When applied to a JSON array, the character `-` indicates one past the last element in the array.
### Classes
<table border="0">
<tr>
<td><a href="basic_json_pointer.md">basic_json_pointer</a></td>
<td>Objects of type <code>basic_json_pointer</code> represent a JSON Pointer.</td>
</tr>
</table>
### Functions
<table border="0">
<tr>
<td><a href="contains.md">contains</a></td>
<td>Returns <code>true</code> if the json document contains the given JSON Pointer</td>
</tr>
<tr>
<td><a href="get.md">get</a></td>
<td>Get a value from a JSON document using JSON Pointer path notation.</td>
</tr>
<tr>
<td><a href="add.md">add</a></td>
<td>Inserts a value in a JSON document using JSON Pointer path notation, or if the path specifies an object member that already has the same key, assigns the new value to that member.</td>
</tr>
<tr>
<td><code>insert</code> (until 0.162.0)</td>
<td>Same as <a href="add_if_absent.md">add_if_absent</a></td>
</tr>
<tr>
<td><a href="add_if_absent.md">add_if_absent</a> (since 0.162.0))</td>
<td>Inserts a value in a JSON document using JSON Pointer path notation, if the path doesn't specify an object member that already has the same key.</td>
</tr>
<tr>
<td><a href="remove.md">remove</a></td>
<td>Removes a value from a JSON document using JSON Pointer path notation.</td>
</tr>
<tr>
<td><a href="replace.md">replace</a></td>
<td>Replaces a value in a JSON document using JSON Pointer path notation.</td>
</tr>
<tr>
<td><a href="flatten.md">flatten<br>unflatten</a></td>
<td>Flattens a json object or array into a single depth object of JSON Pointer-value pairs.</td>
</tr>
</table>
### Examples
#### Select author from second book
```cpp
#include <jsoncons/json.hpp>
#include <jsoncons_ext/jsonpointer/jsonpointer.hpp>
// for brevity
using jsoncons::json;
namespace jsonpointer = jsoncons::jsonpointer;
int main()
{
auto j = json::parse(R"(
[
{ "category": "reference",
"author": "Nigel Rees",
"title": "Sayings of the Century",
"price": 8.95
},
{ "category": "fiction",
"author": "Evelyn Waugh",
"title": "Sword of Honour",
"price": 12.99
}
]
)");
// Using exceptions to report errors
try
{
json result = jsonpointer::get(j, "/1/author");
std::cout << "(1) " << result << '\n';
}
catch (const jsonpointer::jsonpointer_error& e)
{
std::cout << e.what() << '\n';
}
// Using error codes to report errors
std::error_code ec;
const json& result = jsonpointer::get(j, "/0/title", ec);
if (ec)
{
std::cout << ec.message() << '\n';
}
else
{
std::cout << "(2) " << result << '\n';
}
}
```
Output:
```json
(1) "Evelyn Waugh"
(2) "Sayings of the Century"
```
#### Using jsonpointer::json_pointer with jsonpointer::get
```cpp
#include <jsoncons/json.hpp>
#include <jsoncons_ext/jsonpointer/jsonpointer.hpp>
using jsoncons::json;
namespace jsonpointer = jsoncons::jsonpointer;
int main()
{
auto j = json::parse(R"(
{
"a/b": ["bar", "baz"],
"m~n": ["foo", "qux"]
}
)");
jsonpointer::json_pointer ptr; // (since 0.159.0)
// jsonpointer::json_ptr ptr; // (until 0.159.0)
ptr /= "m~n";
ptr /= 1; // (since 0.159.0)
//ptr /= "1"; // (until 0.159.0)
std::cout << "(1) " << ptr << "\n\n";
std::cout << "(2)\n";
for (const auto& item : ptr)
{
std::cout << item << "\n";
}
std::cout << "\n";
json item = jsonpointer::get(j, ptr);
std::cout << "(3) " << item << "\n";
}
```
Output:
```
(1) /m~0n/1
(2)
m~n
1
(3) "qux"
```
#### Add a value to a location after creating objects when missing object keys (since 0.162.0)
```cpp
#include <iostream>
#include <jsoncons/json.hpp>
#include <jsoncons_ext/jsonpointer/jsonpointer.hpp>
using jsoncons::json;
namespace jsonpointer = jsoncons::jsonpointer;
int main()
{
std::vector<std::string> keys = {"foo","bar","baz"};
jsonpointer::json_pointer location;
for (const auto& key : keys)
{
location /= key;
}
json doc;
jsonpointer::add(doc, location, "str", true);
std::cout << pretty_print(doc) << "\n\n";
}
```
Output:
```json
{
"foo": {
"bar": {
"baz": "str"
}
}
}
```
|
