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### jsoncons::decode_json
Decodes a JSON data format to a C++ data structure. `decode_json` will
work for all C++ classes that have [json_type_traits](https://github.com/danielaparker/jsoncons/blob/master/doc/ref/corelib/json_type_traits.md) defined.
```cpp
#include <jsoncons/decode_json.hpp>
template <typename T,typename Source>
T decode_json(const Source& s,
const basic_json_decode_options<Source::value_type>& options
= basic_json_decode_options<Source::value_type>()); (1)
template <typename T,typename CharT>
T decode_json(std::basic_istream<CharT>& is,
const basic_json_decode_options<CharT>& options = basic_json_decode_options<CharT>()); (2)
template <typename T,typename Iterator>
T decode_json(Iterator first, Iterator last,
const basic_json_decode_options<CharT>& options = basic_json_decode_options<CharT>()); (3)
template <typename T,typename Source,typename Allocator,typename TempAllocator>
T decode_json(const allocator_set<Allocator,TempAllocator>& alloc_set,
const Source& s,
const basic_json_decode_options<Source::value_type>& options
= basic_json_decode_options<Source::value_type>()); (4) (since 0.171.0)
template <typename T,typename CharT,typename Allocator,typename TempAllocator>
T decode_json(const allocator_set<Allocator,TempAllocator>& alloc_set,
std::basic_istream<CharT>& is,
const basic_json_decode_options<CharT>& options = basic_json_decode_options<CharT>()); (5) (since 0.171.0)
```
(1) Reads JSON from a contiguous character sequence provided by `s` into a type T, using the specified (or defaulted) [options](basic_json_options.md).
Type 'T' must be an instantiation of [basic_json](../basic_json.md)
or support [json_type_traits](../json_type_traits.md).
(2) Reads JSON from an input stream into a type T, using the specified (or defaulted) [options](basic_json_options.md).
Type 'T' must be an instantiation of [basic_json](../basic_json.md)
or support [json_type_traits](../json_type_traits.md).
(3) Reads JSON from the range [first,last) into a type T, using the specified (or defaulted) [options](basic_json_options.md).
Type 'T' must be an instantiation of [basic_json](../basic_json.md)
or support [json_type_traits](../json_type_traits.md).
Functions (1)-(3) perform encodings using the default json type `basic_json<CharT>`.
Functions (4)-(5) are identical to (1)-(2) except an [allocator_set](allocator_set.md) is passed as an additional argument and
provides allocators for result data and temporary allocations.
#### Exceptions
Throws a [ser_error](ser_error.md) if parsing fails, and a [conv_error](conv_error.md) if type conversion fails.Throws a [ser_error](ser_error.md) if parsing fails, and a [conv_error](conv_error.md) if type conversion fails, and a [conv_error](conv_error.md) if type conversion fails.
### Examples
#### Map with string-tuple pairs
```cpp
#include <iostream>
#include <map>
#include <tuple>
#include <jsoncons/json.hpp>
int main()
{
using employee_collection = std::map<std::string,std::tuple<std::string,std::string,double>>;
std::string s = R"(
{
"Jane Doe": ["Commission","Sales",20000.0],
"John Smith": ["Hourly","Software Engineer",10000.0]
}
)";
employee_collection employees = jsoncons::decode_json<employee_collection>(s);
for (const auto& pair : employees)
{
std::cout << pair.first << ": " << std::get<1>(pair.second) << '\n';
}
}
```
Output:
```
Jane Doe: Sales
John Smith: Software Engineer
```
### See also
[allocator_set](allocator_set.md)
[encode_json](encode_json.md)
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