Similar to C++ streams, but the stream elements are structured JSON data rather than characters.

• Features
• [Parsing Examples](#Parsing Examples)
• [Printing Examples](#Printing Examples)
• Dependencies
• [Other Libraries](#Other Libraries)

Not all parsing of JSON has to happen at once, but rather parsing can be streamed before all JSON is available. This is similar to many SAX parsers, but with jios client code still calls jios and "pulls" data rather than being called like a SAX parser would.

JSON objects and arrays are represented by distinct C++ types and can be "walked" and iterated in for loops like a DOM interface.

jios can be called assuming all data is available or the expecting method can be called to check whether jios is still expecting more data. This can be used in asynchronous code to determine parsing should performed later when more data is available.

Async Example

Source back-end do not have to construct entire json objects in memory and instead data can read data incrementally into custom strongly types C++ objects.

A template library (express.hpp) is included which makes it easy to declare the JSON object members to bind to C++ class members so that such C++ classes can immediately be read and written as JSON.

Expression Example

Three ways jios interoperates with C++ streams:

• included back-end source and sink and read and write with C++ streams.
• C++ types and have insertion (<<) and extraction (>>) defined for C++ streams automatically work with jios. This mechanism can be overloaded when C++ types should be represented as structures JSON rather than JSON strings.
• The jios front-end provides syntactic sugar and semantics that are like C++ streams.

Streams are backed by source and sink back-ends which do not have to operate on textual JSON.

C++ classes generated by Google Protocol Buffers are automatically readable and writable to any jios sources and sinks.

  istringstream ss("1 \"two\" 3");
  int i, j;
  string s;
  json_in(ss) >> i >> s >> j;

  using namespace boost::posix_time;
  istringstream ss("[\"00:01:03\", \"00:00:12\"]");
  time_duration t1, t2;
  ijarray ija = json_in(ss).get().array();
  ija >> t1 >> t2;
  cout << boolalpha << bool(t1 == seconds(63)) << ' '
                    << bool(t2 == seconds(12)) << endl;

outputs

  true true

  istringstream ss("[1, 2, 3]");
  list<int> many;
  json_in(ss) >> many;
  list<int> expect = {1, 2, 3};
  cout << boolalpha << bool(many == expect) << endl;
outputs

true

### Iterate on JSON streams and arrays

```cpp
  istringstream ss("1 2 3 4 5");
  int sum = 0;
  for (ijvalue & v : json_in(ss)) {
    int i;
    if (v.read(i)) {
      sum += i;
    }
  }
  cout << sum << endl;

outputs

  15

  stringstream ss;
  int i = 0;
  ss << "[";
  ijarray ija = json_in(ss).get().array();
  ss << "1 ";
  ija >> i;
  cout << i << endl;
  ss << ", 2 ";
  ija >> i;
  cout << i << endl;
  ss << "]";
  if (ija.at_end()) { cout << "Done!" << endl; }

outputs

  1
  2
  Done!

  stringstream ss;
  ss << R"( { "a":1, "b":2, "c":3 } )";
  int sum = 0;
  for (ijpair & nv : json_in(ss).get().object()) {
    int i;
    if (nv.read(i)) {
      sum += i;
    }
  }
  cout << sum << endl;

outputs

  6

  stringstream ss;
  ss << R"( { "Joe":35, "Jane":33 } )";
  string name1, name2;
  int age1, age2;
  ijobject ijo = json_in(ss).get().object();
  ijo >> tie(name1, age1) >> tie(name2, age2);
  cout << name1 << " is " << age1 - age2 << " years older than "
       << name2 << endl;

outputs

  Joe is 2 years older than Jane 

  jios::json_out(std::cout, '\n') << 1 << 2 << "three";

outputs

  1
  2
  "three"

In the rest of the examples assume

  using namespace std;
  using namespace jios;
  ojstream jout = json_out(cout);

  ojarray oja = jout.put().array();
  for (int i = 0; i < 3; ++i) {
    oja << i;
  }
  oja << endj;

outputs

  [0, 1, 2]

  string b = "BEE";
  jout.put().object() << make_pair("one", 1) << tie("two", b) << endj;

outputs

  {"one":1, "two":"BEE"}

  using namespace boost::posix_time;
  jout.put().array() << seconds(3) << seconds(2) << seconds(1) << endj;

outputs

  ["00:00:03", "00:00:02", "00:00:01"]

Even use such types as JSON object keys.

  using namespace boost::posix_time;
  jout.put().object() << make_pair(seconds(3), "launch")
                      << make_pair(seconds(7), "explode") << endj;

outputs

  {"00:00:03":"launch", "00:00:07":"explode"}

• C++11
• boost
• JSON-C
• Google Protocol Buffers (optional)

There are many C/C++ JSON libraries. www.json.org has a long list of such C and C++ libraries.

A few worth mentioning are

• JSON-C : the C library currently used by jios
• JsonCpp : a C++ library I have used in the past
• https://github.com/Loki-Astari/ThorsSerializer
• https://github.com/rsms/jsont