JSON for Modern C++ 2.1.1
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◆ parse() [5/6]

template<template< typename U, typename V, typename... Args > class ObjectType = std::map, template< typename U, typename... Args > class ArrayType = std::vector, class StringType = std::string, class BooleanType = bool, class NumberIntegerType = std::int64_t, class NumberUnsignedType = std::uint64_t, class NumberFloatType = double, template< typename U > class AllocatorType = std::allocator, template< typename T, typename SFINAE=void > class JSONSerializer = adl_serializer>
static basic_json nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer >::parse ( std::istream &  i,
const parser_callback_t  cb = nullptr 
)
inlinestatic
Parameters
[in,out]istream to read a serialized JSON value from
[in]cba parser callback function of type parser_callback_t which is used to control the deserialization by filtering unwanted values (optional)
Returns
result of the deserialization
Complexity\n Linear in the length of the input. The parser is a predictive
LL(1) parser. The complexity can be higher if the parser callback function cb has a super-linear complexity.
Note
A UTF-8 byte order mark is silently ignored.
Example\n The example below demonstrates the parse() function with
and without callback function.
1#include <json.hpp>
2
3using json = nlohmann::json;
4
5int main()
6{
7 // a JSON text
8 auto text = R"(
9 {
10 "Image": {
11 "Width": 800,
12 "Height": 600,
13 "Title": "View from 15th Floor",
14 "Thumbnail": {
15 "Url": "http://www.example.com/image/481989943",
16 "Height": 125,
17 "Width": 100
18 },
19 "Animated" : false,
20 "IDs": [116, 943, 234, 38793]
21 }
22 }
23 )";
24
25 // fill a stream with JSON text
26 std::stringstream ss;
27 ss << text;
28
29 // parse and serialize JSON
31 std::cout << std::setw(4) << j_complete << "\n\n";
32
33
34 // define parser callback
36 {
37 // skip object elements with key "Thumbnail"
38 if (event == json::parse_event_t::key and parsed == json("Thumbnail"))
39 {
40 return false;
41 }
42 else
43 {
44 return true;
45 }
46 };
47
48 // fill a stream with JSON text
49 ss.clear();
50 ss << text;
51
52 // parse (with callback) and serialize JSON
54 std::cout << std::setw(4) << j_filtered << '\n';
55}
static basic_json array(std::initializer_list< basic_json > init=std::initializer_list< basic_json >())
explicitly create an array from an initializer list
Definition json.hpp:2165
static basic_json parse(T(&array)[N], const parser_callback_t cb=nullptr)
deserialize from an array
Definition json.hpp:6284
void clear() noexcept
clears the contents
Definition json.hpp:5185
parse_event_t
JSON callback events.
Definition json.hpp:1808
@ key
the parser read a key of a value in an object
std::function< bool(int depth, parse_event_t event, basic_json &parsed)> parser_callback_t
per-element parser callback type
Definition json.hpp:1877
a class to store JSON values
Definition json.hpp:1040
basic_json<> json
default JSON class
Definition json.hpp:12369

Output (play with this example online):
{
    "Image": {
        "Animated": false,
        "Height": 600,
        "IDs": [
            116,
            943,
            234,
            38793
        ],
        "Thumbnail": {
            "Height": 125,
            "Url": "http://www.example.com/image/481989943",
            "Width": 100
        },
        "Title": "View from 15th Floor",
        "Width": 800
    }
}

{
    "Image": {
        "Animated": false,
        "Height": 600,
        "IDs": [
            116,
            943,
            234,
            38793
        ],
        "Title": "View from 15th Floor",
        "Width": 800
    }
}

The example code above can be translated with
g++ -std=c++11 -Isrc doc/examples/parse__istream__parser_callback_t.cpp -o parse__istream__parser_callback_t 
See also
parse(const CharT, const parser_callback_t) for a version that reads from a string
Since
version 1.0.0

Definition at line 6352 of file json.hpp.