📝 add more missing examples

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Niels Lohmann 2022-08-04 23:46:17 +02:00
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10 changed files with 198 additions and 7 deletions

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#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
namespace ns
{
// a simple struct to model a person
struct person
{
std::string name;
std::string address;
int age;
};
} // namespace ns
namespace ns
{
void from_json(const json& j, person& p)
{
j.at("name").get_to(p.name);
j.at("address").get_to(p.address);
j.at("age").get_to(p.age);
}
} // namespace ns
int main()
{
json j;
j["name"] = "Ned Flanders";
j["address"] = "744 Evergreen Terrace";
j["age"] = 60;
auto p = j.get<ns::person>();
std::cout << p.name << " (" << p.age << ") lives in " << p.address << std::endl;
}

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Ned Flanders (60) lives in 744 Evergreen Terrace

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#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
namespace ns
{
// a simple struct to model a person (not default constructible)
struct person
{
person(std::string n, std::string a, int aa)
: name(std::move(n)), address(std::move(a)), age(aa)
{}
std::string name;
std::string address;
int age;
};
} // namespace ns
namespace nlohmann
{
template <>
struct adl_serializer<ns::person>
{
static ns::person from_json(const json& j)
{
return {j.at("name"), j.at("address"), j.at("age")};
}
// Here's the catch! You must provide a to_json method! Otherwise, you
// will not be able to convert person to json, since you fully
// specialized adl_serializer on that type
static void to_json(json& j, ns::person p)
{
j["name"] = p.name;
j["address"] = p.address;
j["age"] = p.age;
}
};
} // namespace nlohmann
int main()
{
json j;
j["name"] = "Ned Flanders";
j["address"] = "744 Evergreen Terrace";
j["age"] = 60;
auto p = j.get<ns::person>();
std::cout << p.name << " (" << p.age << ") lives in " << p.address << std::endl;
}

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Ned Flanders (60) lives in 744 Evergreen Terrace

32
docs/examples/to_json.cpp Normal file
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#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
namespace ns
{
// a simple struct to model a person
struct person
{
std::string name;
std::string address;
int age;
};
} // namespace ns
namespace ns
{
void to_json(json& j, const person& p)
{
j = json{ {"name", p.name}, {"address", p.address}, {"age", p.age} };
}
} // namespace ns
int main()
{
ns::person p = {"Ned Flanders", "744 Evergreen Terrace", 60};
json j = p;
std::cout << j << std::endl;
}

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{"address":"744 Evergreen Terrace","age":60,"name":"Ned Flanders"}

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@ -14,8 +14,8 @@ noexcept(::nlohmann::from_json(std::forward<BasicJsonType>(j), detail::identity_
-> decltype(::nlohmann::from_json(std::forward<BasicJsonType>(j), detail::identity_tag<TargetType> {}))
```
This function is usually called by the [`get()`](../basic_json/get.md) function of the
[basic_json](../basic_json) class (either explicit or via conversion operators).
This function is usually called by the [`get()`](../basic_json/get.md) function of the [basic_json](../basic_json)
class (either explicit or via conversion operators).
1. This function is chosen for default-constructible value types.
2. This function is chosen for value types which are not default-constructible.
@ -32,9 +32,41 @@ This function is usually called by the [`get()`](../basic_json/get.md) function
Copy of the JSON value, converted to `ValueType`
!!! note
## Examples
This documentation page is a stub.
??? example "Example: (1) Default-constructible type"
The example below shows how a `from_json` function can be implemented for a user-defined type. This function is
called by the `adl_serializer` when `get<ns::person>()` is called.
```cpp
--8<-- "examples/from_json__default_constructible.cpp"
```
Output:
```json
--8<-- "examples/from_json__default_constructible.output"
```
??? example "Example: (2) Non-default-constructible type"
The example below shows how a `from_json` is implemented as part of a specialization of the `adl_serializer` to
realize the conversion of a non-default-constructible type.
```cpp
--8<-- "examples/from_json__non_default_constructible.cpp"
```
Output:
```json
--8<-- "examples/from_json__non_default_constructible.output"
```
## See also
- [to_json](to_json.md)
## Version history

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@ -17,9 +17,26 @@ This function is usually called by the constructors of the [basic_json](../basic
`val` (in)
: value to read from
!!! note
## Examples
This documentation page is a stub.
??? example
The example below shows how a `to_json` function can be implemented for a user-defined type. This function is called
by the `adl_serializer` when the constructor `basic_json(ns::person)` is called.
```cpp
--8<-- "examples/to_json.cpp"
```
Output:
```json
--8<-- "examples/to_json.output"
```
## See also
- [from_json](from_json.md)
## Version history

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@ -19,6 +19,23 @@ using json_serializer = JSONSerializer<T, SFINAE>;
The default values for `json_serializer` is [`adl_serializer`](../adl_serializer).
## Examples
??? example
The example below shows how a conversion of a non-default-constructible type is implemented via a specialization of
the `adl_serializer`.
```cpp
--8<-- "examples/from_json__non_default_constructible.cpp"
```
Output:
```json
--8<-- "examples/from_json__non_default_constructible.output"
```
## Version history
- Since version 2.0.0.

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@ -10,7 +10,7 @@ namespace ns {
std::string address;
int age;
};
}
} // namespace ns
ns::person p = {"Ned Flanders", "744 Evergreen Terrace", 60};