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### jsoncons::json_decoder
```cpp
#include <jsoncons/json_decoder.hpp>
template <typename Json,typename TempAllocator>
json_decoder
```
#### Member types
Member type |Definition
------------------------------------|------------------------------
`result_allocator_type`|Json::allocator_type (until 0.171.0)
`allocator_type`|Json::allocator_type (since 0.171.0)
`temp_allocator_type`|TempAllocator
#### Constructors
json_decoder(result_allocator_arg_t,
const result_allocator_type& alloc); (1) (until 0.171.0)
json_decoder(result_allocator_arg_t,
const result_allocator_type& alloc,
const temp_allocator_type& temp_alloc); (1) (until 0.171.0)
json_decoder(const allocator_type& alloc = allocator_type(),
const temp_allocator_type& temp_alloc = temp_allocator_type()); (1) (since 0.171.0)
json_decoder(const temp_allocator_type& temp_alloc =
temp_allocator_type()); (2) (until 0.171.0)
json_decoder(temp_allocator_arg_t,
const temp_allocator_type& temp_alloc); (2) (since 0.171.0)
#### Member functions
allocator_type get_allocator() const
Returns the allocator associated with the json value.
bool is_valid() const
Checks if the decoder contains a valid `basic_json` value.
Initially `is_valid()` is false, becomes `true` when a `basic_json`
value has been received, and becomes false when `get_result()` is called.
Json get_result()
Returns the json value `v` stored in the decoder as `std::move(v)`.
If before calling this function `is_valid()` is false, an `assertion_error` is thrown.
After `get_result()` is called, 'is_valid()' becomes false.
Once the result has been retrieved, `get_result` cannot be called again until
another `basic_json` value has been received.
### Examples
#### Decode a JSON text using stateful result and work allocators
Input JSON file `book_catalog.json`:
```json
[
{
"author" : "Haruki Murakami",
"title" : "Hard-Boiled Wonderland and the End of the World",
"isbn" : "0679743464",
"publisher" : "Vintage",
"date" : "1993-03-02",
"price": 18.90
},
{
"author" : "Graham Greene",
"title" : "The Comedians",
"isbn" : "0099478374",
"publisher" : "Vintage Classics",
"date" : "2005-09-21",
"price": 15.74
}
]
```
```cpp
int main()
{
// Given allocator my_alloc with a single-argument constructor my_alloc(int),
// use my_alloc(1) to allocate basic_json memory, my_alloc(2) to allocate
// working memory used by json_decoder, and my_alloc(3) to allocate
// working memory used by basic_json_reader.
using my_json = basic_json<char,sorted_policy,my_alloc>;
std::ifstream is("book_catalog.json");
json_decoder<my_json,my_alloc> decoder(my_alloc(1),my_alloc(2));
basic_json_reader<char,stream_source<char>,my_alloc> reader(is, decoder, my_alloc(3));
reader.read();
my_json j = decoder.get_result();
std::cout << pretty_print(j) << "\n";
}
```
Output:
```
[
{
"author": "Haruki Murakami",
"date": "1993-03-02",
"isbn": "0679743464",
"price": 18.9,
"publisher": "Vintage",
"title": "Hard-Boiled Wonderland and the End of the World"
},
{
"author": "Graham Greene",
"date": "2005-09-21",
"isbn": "0099478374",
"price": 15.74,
"publisher": "Vintage Classics",
"title": "The Comedians"
}
]
```
#### Decode a CSV text using stateful result and work allocators
Input CSV file `bond_yields.csv`:
```
Date,1Y,2Y,3Y,5Y
2017-01-09,0.0062,0.0075,0.0083,0.011
2017-01-08,0.0063,0.0076,0.0084,0.0112
2017-01-08,0.0063,0.0076,0.0084,0.0112
```
```cpp
int main()
{
// Given allocator my_alloc with a single-argument constructor my_alloc(int),
// use my_alloc(1) to allocate basic_json memory, my_alloc(2) to allocate
// working memory used by json_decoder, and my_alloc(3) to allocate
// working memory used by basic_csv_reader.
using my_json = basic_json<char,sorted_policy,my_alloc>;
auto options = csv::csv_options{}
.assume_header(true);
std::ifstream is("bond_yields.csv");
json_decoder<my_json,my_alloc> decoder(my_alloc(1),my_alloc(2));
csv::basic_csv_reader<char,stream_source<char>,free_list_allocator<char>> reader(is, decoder, options, my_alloc(3));
reader.read();
my_json j = decoder.get_result();
std::cout << pretty_print(j) << "\n";
}
```
Output:
```
[
{
"1Y": 0.0062,
"2Y": 0.0075,
"3Y": 0.0083,
"5Y": 0.011,
"Date": "2017-01-09"
},
{
"1Y": 0.0063,
"2Y": 0.0076,
"3Y": 0.0084,
"5Y": 0.0112,
"Date": "2017-01-08"
},
{
"1Y": 0.0063,
"2Y": 0.0076,
"3Y": 0.0084,
"5Y": 0.0112,
"Date": "2017-01-08"
}
]
```
### See also
[basic_json_visitor](basic_json_visitor.md)
|
