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2026-07-09 12:05:10 +00:00 · 2026-07-08 18:19:46 +00:00
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+# nlohmann::basic_json::from_msgpack
+
+```
+// (1)
+template<typename InputType>
+static basic_json from_msgpack(InputType&& i,
+                               const bool strict = true,
+                               const bool allow_exceptions = true);
+// (2)
+template<typename IteratorType>
+static basic_json from_msgpack(IteratorType first, IteratorType last,
+                               const bool strict = true,
+                               const bool allow_exceptions = true);
+```
+
+Deserializes a given input to a JSON value using the MessagePack serialization format.
+
+1. Reads from a compatible input.
+1. Reads from an iterator range.
+
+The exact mapping and its limitations are described on a [dedicated page](https://json.nlohmann.me/features/binary_formats/messagepack/index.md).
+
+## Template parameters
+
+`InputType` : A compatible input, for instance:
+
+```
+- an `std::istream` object
+- a `FILE` pointer
+- a C-style array of characters
+- a pointer to a null-terminated string of single byte characters
+- an object `obj` for which `begin(obj)` and `end(obj)` produces a valid pair of iterators.
+```
+
+`IteratorType` : a compatible iterator type
+
+## Parameters
+
+`i` (in) : an input in MessagePack format convertible to an input adapter
+
+`first` (in) : iterator to the start of the input
+
+`last` (in) : iterator to the end of the input
+
+`strict` (in) : whether to expect the input to be consumed until EOF (`true` by default)
+
+`allow_exceptions` (in) : whether to throw exceptions in case of a parse error (optional, `true` by default)
+
+## Return value
+
+deserialized JSON value; in case of a parse error and `allow_exceptions` set to `false`, the return value will be `value_t::discarded`. The latter can be checked with [`is_discarded`](https://json.nlohmann.me/api/basic_json/is_discarded/index.md).
+
+## Exception safety
+
+Strong guarantee: if an exception is thrown, there are no changes in the JSON value.
+
+## Exceptions
+
+- Throws [parse_error.110](https://json.nlohmann.me/home/exceptions/#jsonexceptionparse_error110) if the given input ends prematurely or the end of the file was not reached when `strict` was set to true
+- Throws [parse_error.112](https://json.nlohmann.me/home/exceptions/#jsonexceptionparse_error112) if unsupported features from MessagePack were used in the given input or if the input is not valid MessagePack
+- Throws [parse_error.113](https://json.nlohmann.me/home/exceptions/#jsonexceptionparse_error113) if a string was expected as a map key, but not found
+
+## Complexity
+
+Linear in the size of the input.
+
+## Examples
+
+Example
+
+The example shows the deserialization of a byte vector in MessagePack format to a JSON value.
+
+```
+#include <iostream>
+#include <iomanip>
+#include <nlohmann/json.hpp>
+
+using json = nlohmann::json;
+
+int main()
+{
+    // create byte vector
+    std::vector<std::uint8_t> v = {0x82, 0xa7, 0x63, 0x6f, 0x6d, 0x70, 0x61, 0x63,
+                                   0x74, 0xc3, 0xa6, 0x73, 0x63, 0x68, 0x65, 0x6d,
+                                   0x61, 0x00
+                                  };
+
+    // deserialize it with MessagePack
+    json j = json::from_msgpack(v);
+
+    // print the deserialized JSON value
+    std::cout << std::setw(2) << j << std::endl;
+}
+```
+
+Output:
+
+```
+{
+  "compact": true,
+  "schema": 0
+}
+```
+
+## See also
+
+- [to_msgpack](https://json.nlohmann.me/api/basic_json/to_msgpack/index.md) create a MessagePack serialization of a JSON value
+- [from_cbor](https://json.nlohmann.me/api/basic_json/from_cbor/index.md) create a JSON value from an input in CBOR format
+- [from_bson](https://json.nlohmann.me/api/basic_json/from_bson/index.md) create a JSON value from an input in BSON format
+- [from_ubjson](https://json.nlohmann.me/api/basic_json/from_ubjson/index.md) create a JSON value from an input in UBJSON format
+- [from_bjdata](https://json.nlohmann.me/api/basic_json/from_bjdata/index.md) create a JSON value from an input in BJData format
+
+## Version history
+
+- Added in version 2.0.9.
+- Parameter `start_index` since version 2.1.1.
+- Changed to consume input adapters, removed `start_index` parameter, and added `strict` parameter in version 3.0.0.
+- Added `allow_exceptions` parameter in version 3.2.0.
+
+Deprecation
+
+- Overload (2) replaces calls to `from_msgpack` with a pointer and a length as first two parameters, which has been deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like `from_msgpack(ptr, len, ...);` with `from_msgpack(ptr, ptr+len, ...);`.
+- Overload (2) replaces calls to `from_msgpack` with a pair of iterators as their first parameter, which has been deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like `from_msgpack({ptr, ptr+len}, ...);` with `from_msgpack(ptr, ptr+len, ...);`.
+
+You should be warned by your compiler with a `-Wdeprecated-declarations` warning if you are using a deprecated function.