deploy: 7c9208bfb3

2026-07-09 03:55:09 +00:00 · 2026-07-08 18:19:46 +00:00
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+# nlohmann::basic_json::get_to
+
+```
+template<typename ValueType>
+ValueType& get_to(ValueType& v) const noexcept(
+    noexcept(JSONSerializer<ValueType>::from_json(
+        std::declval<const basic_json_t&>(), v)));
+```
+
+Explicit type conversion between the JSON value and a compatible value. The value is filled into the input parameter by calling the `json_serializer<ValueType>` `from_json()` method.
+
+The function is equivalent to executing
+
+```
+ValueType v;
+JSONSerializer<ValueType>::from_json(*this, v);
+```
+
+This overload is chosen if:
+
+- `ValueType` is not `basic_json`,
+- `json_serializer<ValueType>` has a `from_json()` method of the form `void from_json(const basic_json&, ValueType&)`
+
+## Template parameters
+
+`ValueType` : the value type to return
+
+## Return value
+
+the input parameter, allowing chaining calls
+
+## Exceptions
+
+Depends on what `json_serializer<ValueType>` `from_json()` method throws
+
+## Complexity
+
+Depends on the `json_serializer<ValueType>::from_json()` implementation.
+
+## Examples
+
+Example
+
+The example below shows several conversions from JSON values to other types. There a few things to note: (1) Floating-point numbers can be converted to integers, (2) A JSON array can be converted to a standard `std::vector<short>`, (3) A JSON object can be converted to C++ associative containers such as `#cpp std::unordered_map<std::string, json>`.
+
+```
+#include <iostream>
+#include <unordered_map>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    // create a JSON value with different types
+    json json_types =
+    {
+        {"boolean", true},
+        {
+            "number", {
+                {"integer", 42},
+                {"floating-point", 17.23}
+            }
+        },
+        {"string", "Hello, world!"},
+        {"array", {1, 2, 3, 4, 5}},
+        {"null", nullptr}
+    };
+
+    bool v1;
+    int v2;
+    short v3;
+    float v4;
+    int v5;
+    std::string v6;
+    std::vector<short> v7;
+    std::unordered_map<std::string, json> v8;
+
+    // use explicit conversions
+    json_types["boolean"].get_to(v1);
+    json_types["number"]["integer"].get_to(v2);
+    json_types["number"]["integer"].get_to(v3);
+    json_types["number"]["floating-point"].get_to(v4);
+    json_types["number"]["floating-point"].get_to(v5);
+    json_types["string"].get_to(v6);
+    json_types["array"].get_to(v7);
+    json_types.get_to(v8);
+
+    // print the conversion results
+    std::cout << v1 << '\n';
+    std::cout << v2 << ' ' << v3 << '\n';
+    std::cout << v4 << ' ' << v5 << '\n';
+    std::cout << v6 << '\n';
+
+    for (auto i : v7)
+    {
+        std::cout << i << ' ';
+    }
+    std::cout << "\n\n";
+
+    for (auto i : v8)
+    {
+        std::cout << i.first << ": " << i.second << '\n';
+    }
+}
+```
+
+Output:
+
+```
+1
+42 42
+17.23 17
+Hello, world!
+1 2 3 4 5 
+
+string: "Hello, world!"
+number: {"floating-point":17.23,"integer":42}
+null: null
+boolean: true
+array: [1,2,3,4,5]
+```
+
+## See also
+
+- [get](https://json.nlohmann.me/api/basic_json/get/index.md) get a value (explicit conversion)
+- [get_ref](https://json.nlohmann.me/api/basic_json/get_ref/index.md) get a reference to the stored value
+- [get_ptr](https://json.nlohmann.me/api/basic_json/get_ptr/index.md) get a pointer to the stored value
+- [Converting values](https://json.nlohmann.me/features/conversions/index.md) - the type conversions article
+
+## Version history
+
+- Since version 3.3.0.