1# <small>nlohmann::basic_json::</small>from_msgpack 2 3```cpp 4// (1) 5template<typename InputType> 6static basic_json from_msgpack(InputType&& i, 7 const bool strict = true, 8 const bool allow_exceptions = true); 9// (2) 10template<typename IteratorType> 11static basic_json from_msgpack(IteratorType first, IteratorType last, 12 const bool strict = true, 13 const bool allow_exceptions = true); 14``` 15 16Deserializes a given input to a JSON value using the MessagePack serialization format. 17 181. Reads from a compatible input. 192. Reads from an iterator range. 20 21The exact mapping and its limitations is described on a [dedicated page](../../features/binary_formats/messagepack.md). 22 23## Template parameters 24 25`InputType` 26: A compatible input, for instance: 27 28 - an `std::istream` object 29 - a `FILE` pointer 30 - a C-style array of characters 31 - a pointer to a null-terminated string of single byte characters 32 - an object `obj` for which `begin(obj)` and `end(obj)` produces a valid pair of iterators. 33 34`IteratorType` 35: a compatible iterator type 36 37## Parameters 38 39`i` (in) 40: an input in MessagePack format convertible to an input adapter 41 42`first` (in) 43: iterator to start of the input 44 45`last` (in) 46: iterator to end of the input 47 48`strict` (in) 49: whether to expect the input to be consumed until EOF (`#!cpp true` by default) 50 51`allow_exceptions` (in) 52: whether to throw exceptions in case of a parse error (optional, `#!cpp true` by default) 53 54## Return value 55 56deserialized JSON value; in case of a parse error and `allow_exceptions` set to `#!cpp false`, the return value will be 57`value_t::discarded`. The latter can be checked with [`is_discarded`](is_discarded.md). 58 59## Exception safety 60 61Strong guarantee: if an exception is thrown, there are no changes in the JSON value. 62 63## Exceptions 64 65- Throws [parse_error.110](../../home/exceptions.md#jsonexceptionparse_error110) if the given input ends prematurely or 66 the end of file was not reached when `strict` was set to true 67- Throws [parse_error.112](../../home/exceptions.md#jsonexceptionparse_error112) if unsupported features from 68 MessagePack were used in the given input or if the input is not valid MessagePack 69- Throws [parse_error.113](../../home/exceptions.md#jsonexceptionparse_error113) if a string was expected as map key, 70 but not found 71 72## Complexity 73 74Linear in the size of the input. 75 76## Examples 77 78??? example 79 80 The example shows the deserialization of a byte vector in MessagePack format to a JSON value. 81 82 ```cpp 83 --8<-- "examples/from_msgpack.cpp" 84 ``` 85 86 Output: 87 88 ```json 89 --8<-- "examples/from_msgpack.output" 90 ``` 91 92## Version history 93 94- Added in version 2.0.9. 95- Parameter `start_index` since version 2.1.1. 96- Changed to consume input adapters, removed `start_index` parameter, and added `strict` parameter in version 3.0.0. 97- Added `allow_exceptions` parameter in version 3.2.0. 98 99!!! warning "Deprecation" 100 101 - Overload (2) replaces calls to `from_msgpack` with a pointer and a length as first two parameters, which has been 102 deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like 103 `#!cpp from_msgpack(ptr, len, ...);` with `#!cpp from_msgpack(ptr, ptr+len, ...);`. 104 - Overload (2) replaces calls to `from_cbor` with a pair of iterators as their first parameter, which has been 105 deprecated in version 3.8.0. This overload will be removed in version 4.0.0. Please replace all calls like 106 `#!cpp from_msgpack({ptr, ptr+len}, ...);` with `#!cpp from_msgpack(ptr, ptr+len, ...);`. 107 108 You should be warned by your compiler with a `-Wdeprecated-declarations` warning if you are using a deprecated 109 function. 110