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Exceptions

Overview

Base type

All exceptions inherit from class json::exception (which in turn inherits from std::exception). It is used as the base class for all exceptions thrown by the basic_json class. This class can hence be used as "wildcard" to catch exceptions.

uml diagram

Switch off exceptions

Exceptions are used widely within the library. They can, however, be switched off with either using the compiler flag -fno-exceptions or by defining the symbol JSON_NOEXCEPTION. In this case, exceptions are replaced by abort() calls. You can further control this behavior by defining JSON_THROW_USER (overriding throw), JSON_TRY_USER (overriding try), and JSON_CATCH_USER (overriding catch).

Note that JSON_THROW_USER should leave the current scope (e.g., by throwing or aborting), as continuing after it may yield undefined behavior.

Parse errors

This exception is thrown by the library when a parse error occurs. Parse errors can occur during the deserialization of JSON text, CBOR, MessagePack, as well as when using JSON Patch.

Exceptions have ids 1xx.

Byte index

Member byte holds the byte index of the last read character in the input file.

For an input with n bytes, 1 is the index of the first character and n+1 is the index of the terminating null byte or the end of file. This also holds true when reading a byte vector (CBOR or MessagePack).

Example

The following code shows how a parse_error exception can be caught.

#include <iostream>
#include <nlohmann/json.hpp>

using json = nlohmann::json;

int main()
{
    try
    {
        // parsing input with a syntax error
        json::parse("[1,2,3,]");
    }
    catch (json::parse_error& e)
    {
        // output exception information
        std::cout << "message: " << e.what() << '\n'
                  << "exception id: " << e.id << '\n'
                  << "byte position of error: " << e.byte << std::endl;
    }
}

Output:

message: [json.exception.parse_error.101] parse error at line 1, column 8: syntax error while parsing value - unexpected ']'; expected '[', '{', or a literal
exception id: 101
byte position of error: 8

json.exception.parse_error.101

This error indicates a syntax error while deserializing a JSON text. The error message describes that an unexpected token (character) was encountered, and the member byte indicates the error position.

Example message

Input ended prematurely:

[json.exception.parse_error.101] parse error at 2: unexpected end of input; expected string literal

No input:

[json.exception.parse_error.101] parse error at line 1, column 1: syntax error while parsing value - unexpected end of input; expected '[', '{', or a literal

Control character was not escaped:

[json.exception.parse_error.101] parse error at line 1, column 2: syntax error while parsing value - invalid string: control character U+0009 (HT) must be escaped to \u0009 or \\; last read: '"<U+0009>'"

String was not closed:

[json.exception.parse_error.101] parse error at line 1, column 2: syntax error while parsing value - invalid string: missing closing quote; last read: '"'

Invalid number format:

[json.exception.parse_error.101] parse error at line 1, column 3: syntax error while parsing value - invalid number; expected '+', '-', or digit after exponent; last read: '1E'

\u was not be followed by four hex digits:

[json.exception.parse_error.101] parse error at line 1, column 6: syntax error while parsing value - invalid string: '\u' must be followed by 4 hex digits; last read: '"\u01"'

Invalid UTF-8 surrogate pair:

[json.exception.parse_error.101] parse error at line 1, column 13: syntax error while parsing value - invalid string: surrogate U+DC00..U+DFFF must follow U+D800..U+DBFF; last read: '"\uD7FF\uDC00'"

Invalid UTF-8 byte:

[json.exception.parse_error.101] parse error at line 3, column 24: syntax error while parsing value - invalid string: ill-formed UTF-8 byte; last read: '"vous \352t'

Tip

  • Make sure the input is correctly read. Try to write the input to standard output to check if, for instance, the input file was successfully openened.
  • Paste the input to a JSON validator like http://jsonlint.com or a tool like jq.

json.exception.parse_error.102

JSON uses the \uxxxx format to describe Unicode characters. Code points above above 0xFFFF are split into two \uxxxx entries ("surrogate pairs"). This error indicates that the surrogate pair is incomplete or contains an invalid code point.

Example message

parse error at 14: missing or wrong low surrogate

json.exception.parse_error.103

Unicode supports code points up to 0x10FFFF. Code points above 0x10FFFF are invalid.

Example message

parse error: code points above 0x10FFFF are invalid

json.exception.parse_error.104

RFC 6902 requires a JSON Patch document to be a JSON document that represents an array of objects.

Example message

[json.exception.parse_error.104] parse error: JSON patch must be an array of objects

json.exception.parse_error.105

An operation of a JSON Patch document must contain exactly one "op" member, whose value indicates the operation to perform. Its value must be one of "add", "remove", "replace", "move", "copy", or "test"; other values are errors.

Example message

[json.exception.parse_error.105] parse error: operation 'add' must have member 'value'
[json.exception.parse_error.105] parse error: operation 'copy' must have string member 'from'
[json.exception.parse_error.105] parse error: operation value 'foo' is invalid

json.exception.parse_error.106

An array index in a JSON Pointer (RFC 6901) may be 0 or any number without a leading 0.

Example message

[json.exception.parse_error.106] parse error: array index '01' must not begin with '0'

json.exception.parse_error.107

A JSON Pointer must be a Unicode string containing a sequence of zero or more reference tokens, each prefixed by a / character.

Example message

[json.exception.parse_error.107] parse error at byte 1: JSON pointer must be empty or begin with '/' - was: 'foo'

json.exception.parse_error.108

In a JSON Pointer, only ~0 and ~1 are valid escape sequences.

Example message

[json.exception.parse_error.108] parse error: escape character '~' must be followed with '0' or '1'

json.exception.parse_error.109

A JSON Pointer array index must be a number.

Example message

[json.exception.parse_error.109] parse error: array index 'one' is not a number
[json.exception.parse_error.109] parse error: array index '+1' is not a number

json.exception.parse_error.110

When parsing CBOR or MessagePack, the byte vector ends before the complete value has been read.

Example message

[json.exception.parse_error.110] parse error at byte 5: syntax error while parsing CBOR string: unexpected end of input
[json.exception.parse_error.110] parse error at byte 2: syntax error while parsing UBJSON value: expected end of input; last byte: 0x5A

json.exception.parse_error.112

Not all types of CBOR or MessagePack are supported. This exception occurs if an unsupported byte was read.

Example message

[json.exception.parse_error.112] parse error at byte 1: syntax error while parsing CBOR value: invalid byte: 0x1C

json.exception.parse_error.113

While parsing a map key, a value that is not a string has been read.

Example message

[json.exception.parse_error.113] parse error at byte 2: syntax error while parsing CBOR string: expected length specification (0x60-0x7B) or indefinite string type (0x7F); last byte: 0xFF
[json.exception.parse_error.113] parse error at byte 2: syntax error while parsing MessagePack string: expected length specification (0xA0-0xBF, 0xD9-0xDB); last byte: 0xFF
[json.exception.parse_error.113] parse error at byte 2: syntax error while parsing UBJSON char: byte after 'C' must be in range 0x00..0x7F; last byte: 0x82

json.exception.parse_error.114

The parsing of the corresponding BSON record type is not implemented (yet).

Example message

[json.exception.parse_error.114] parse error at byte 5: Unsupported BSON record type 0xFF

Iterator errors

This exception is thrown if iterators passed to a library function do not match the expected semantics.

Exceptions have ids 2xx.

Example

The following code shows how an invalid_iterator exception can be caught.

#include <iostream>
#include <nlohmann/json.hpp>

using json = nlohmann::json;

int main()
{
    try
    {
        // calling iterator::key() on non-object iterator
        json j = "string";
        json::iterator it = j.begin();
        auto k = it.key();
    }
    catch (json::invalid_iterator& e)
    {
        // output exception information
        std::cout << "message: " << e.what() << '\n'
                  << "exception id: " << e.id << std::endl;
    }
}

Output:

message: [json.exception.invalid_iterator.207] cannot use key() for non-object iterators
exception id: 207

json.exception.invalid_iterator.201

The iterators passed to constructor basic_json(InputIT first, InputIT last) are not compatible, meaning they do not belong to the same container. Therefore, the range (first, last) is invalid.

Example message

[json.exception.invalid_iterator.201] iterators are not compatible

json.exception.invalid_iterator.202

In an erase or insert function, the passed iterator @a pos does not belong to the JSON value for which the function was called. It hence does not define a valid position for the deletion/insertion.

Example message

[json.exception.invalid_iterator.202] iterator does not fit current value
[json.exception.invalid_iterator.202] iterators first and last must point to objects

json.exception.invalid_iterator.203

Either iterator passed to function erase(IteratorType first, IteratorType last) does not belong to the JSON value from which values shall be erased. It hence does not define a valid range to delete values from.

Example message

[json.exception.invalid_iterator.203] iterators do not fit current value

json.exception.invalid_iterator.204

When an iterator range for a primitive type (number, boolean, or string) is passed to a constructor or an erase function, this range has to be exactly (begin(), end()), because this is the only way the single stored value is expressed. All other ranges are invalid.

Example message

[json.exception.invalid_iterator.204] iterators out of range

json.exception.invalid_iterator.205

When an iterator for a primitive type (number, boolean, or string) is passed to an erase function, the iterator has to be the begin() iterator, because it is the only way to address the stored value. All other iterators are invalid.

Example message

[json.exception.invalid_iterator.205] iterator out of range

json.exception.invalid_iterator.206

The iterators passed to constructor basic_json(InputIT first, InputIT last) belong to a JSON null value and hence to not define a valid range.

Example message

[json.exception.invalid_iterator.206] cannot construct with iterators from null

json.exception.invalid_iterator.207

The key() member function can only be used on iterators belonging to a JSON object, because other types do not have a concept of a key.

Example message

[json.exception.invalid_iterator.207] cannot use key() for non-object iterators

json.exception.invalid_iterator.208

The operator[] to specify a concrete offset cannot be used on iterators belonging to a JSON object, because JSON objects are unordered.

Example message

[json.exception.invalid_iterator.208] cannot use operator[] for object iterators

json.exception.invalid_iterator.209

The offset operators (+, -, +=, -=) cannot be used on iterators belonging to a JSON object, because JSON objects are unordered.

Example message

[json.exception.invalid_iterator.209] cannot use offsets with object iterators

json.exception.invalid_iterator.210

The iterator range passed to the insert function are not compatible, meaning they do not belong to the same container. Therefore, the range (first, last) is invalid.

Example message

[json.exception.invalid_iterator.210] iterators do not fit

json.exception.invalid_iterator.211

The iterator range passed to the insert function must not be a subrange of the container to insert to.

Example message

[json.exception.invalid_iterator.211] passed iterators may not belong to container

json.exception.invalid_iterator.212

When two iterators are compared, they must belong to the same container.

Example message

[json.exception.invalid_iterator.212] cannot compare iterators of different containers

json.exception.invalid_iterator.213

The order of object iterators cannot be compared, because JSON objects are unordered.

Example message

[json.exception.invalid_iterator.213] cannot compare order of object iterators

json.exception.invalid_iterator.214

Cannot get value for iterator: Either the iterator belongs to a null value or it is an iterator to a primitive type (number, boolean, or string), but the iterator is different to begin().

Example message

[json.exception.invalid_iterator.214] cannot get value

Type errors

This exception is thrown in case of a type error; that is, a library function is executed on a JSON value whose type does not match the expected semantics.

Exceptions have ids 3xx.

Example

The following code shows how a type_error exception can be caught.

#include <iostream>
#include <nlohmann/json.hpp>

using json = nlohmann::json;

int main()
{
    try
    {
        // calling push_back() on a string value
        json j = "string";
        j.push_back("another string");
    }
    catch (json::type_error& e)
    {
        // output exception information
        std::cout << "message: " << e.what() << '\n'
                  << "exception id: " << e.id << std::endl;
    }
}

Output:

message: [json.exception.type_error.308] cannot use push_back() with string
exception id: 308

json.exception.type_error.301

To create an object from an initializer list, the initializer list must consist only of a list of pairs whose first element is a string. When this constraint is violated, an array is created instead.

Example message

[json.exception.type_error.301] cannot create object from initializer list

json.exception.type_error.302

During implicit or explicit value conversion, the JSON type must be compatible to the target type. For instance, a JSON string can only be converted into string types, but not into numbers or boolean types.

Example message

[json.exception.type_error.302] type must be object, but is null
[json.exception.type_error.302] type must be string, but is object

json.exception.type_error.303

To retrieve a reference to a value stored in a basic_json object with get_ref, the type of the reference must match the value type. For instance, for a JSON array, the ReferenceType must be array_t &.

Example message

[json.exception.type_error.303] incompatible ReferenceType for get_ref, actual type is object
[json.exception.type_error.303] incompatible ReferenceType for get_ref, actual type is number"

json.exception.type_error.304

The at() member functions can only be executed for certain JSON types.

Example message

[json.exception.type_error.304] cannot use at() with string
[json.exception.type_error.304] cannot use at() with number

json.exception.type_error.305

The operator[] member functions can only be executed for certain JSON types.

Example message

[json.exception.type_error.305] cannot use operator[] with a string argument with array
[json.exception.type_error.305] cannot use operator[] with a numeric argument with object

json.exception.type_error.306

The value() member functions can only be executed for certain JSON types.

Example message

[json.exception.type_error.306] cannot use value() with number

json.exception.type_error.307

The erase() member functions can only be executed for certain JSON types.

Example message

[json.exception.type_error.307] cannot use erase() with string

json.exception.type_error.308

The push_back() and operator+= member functions can only be executed for certain JSON types.

Example message

[json.exception.type_error.308] cannot use push_back() with string

json.exception.type_error.309

The insert() member functions can only be executed for certain JSON types.

Example message

[json.exception.type_error.309] cannot use insert() with array
[json.exception.type_error.309] cannot use insert() with number

json.exception.type_error.310

The swap() member functions can only be executed for certain JSON types.

Example message

[json.exception.type_error.310] cannot use swap() with number

json.exception.type_error.311

The emplace() and emplace_back() member functions can only be executed for certain JSON types.

Example message

[json.exception.type_error.311] cannot use emplace() with number
[json.exception.type_error.311] cannot use emplace_back() with number

json.exception.type_error.312

The update() member functions can only be executed for certain JSON types.

Example message

[json.exception.type_error.312] cannot use update() with array

json.exception.type_error.313

The unflatten function converts an object whose keys are JSON Pointers back into an arbitrary nested JSON value. The JSON Pointers must not overlap, because then the resulting value would not be well defined.

Example message

[json.exception.type_error.313] invalid value to unflatten

json.exception.type_error.314

The unflatten function only works for an object whose keys are JSON Pointers.

Example message

Calling unflatten() on an array [1,2,3]:

[json.exception.type_error.314] only objects can be unflattened

json.exception.type_error.315

The unflatten() function only works for an object whose keys are JSON Pointers and whose values are primitive.

Example message

Calling unflatten() on an object {"/1", [1,2,3]}:

[json.exception.type_error.315] values in object must be primitive

json.exception.type_error.316

The dump() function only works with UTF-8 encoded strings; that is, if you assign a std::string to a JSON value, make sure it is UTF-8 encoded.

Example message

Calling dump() on a JSON value containing an ISO 8859-1 encoded string:

[json.exception.type_error.316] invalid UTF-8 byte at index 15: 0x6F

Tip

  • Store the source file with UTF-8 encoding.
  • Pass an error handler as last parameter to the dump() function to avoid this exception:
    • json::error_handler_t::replace will replace invalid bytes sequences with U+FFFD
    • json::error_handler_t::ignore will silently ignore invalid byte sequences

json.exception.type_error.317

The dynamic type of the object cannot be represented in the requested serialization format (e.g. a raw true or null JSON object cannot be serialized to BSON)

Example message

Serializing null to BSON:

[json.exception.type_error.317] to serialize to BSON, top-level type must be object, but is null
Serializing [1,2,3] to BSON:
[json.exception.type_error.317] to serialize to BSON, top-level type must be object, but is array

Tip

Encapsulate the JSON value in an object. That is, instead of serializing true, serialize {"value": true}

Out of range

This exception is thrown in case a library function is called on an input parameter that exceeds the expected range, for instance in case of array indices or nonexisting object keys.

Exceptions have ids 4xx.

Example

The following code shows how an out_of_range exception can be caught.

#include <iostream>
#include <nlohmann/json.hpp>

using json = nlohmann::json;

int main()
{
    try
    {
        // calling at() for an invalid index
        json j = {1, 2, 3, 4};
        j.at(4) = 10;
    }
    catch (json::out_of_range& e)
    {
        // output exception information
        std::cout << "message: " << e.what() << '\n'
                  << "exception id: " << e.id << std::endl;
    }
}

Output:

message: [json.exception.out_of_range.401] array index 4 is out of range
exception id: 401

json.exception.out_of_range.401

The provided array index i is larger than size-1.

Example message

array index 3 is out of range

json.exception.out_of_range.402

The special array index - in a JSON Pointer never describes a valid element of the array, but the index past the end. That is, it can only be used to add elements at this position, but not to read it.

Example message

array index '-' (3) is out of range

json.exception.out_of_range.403

The provided key was not found in the JSON object.

Example message

key 'foo' not found

json.exception.out_of_range.404

A reference token in a JSON Pointer could not be resolved.

Example message

unresolved reference token 'foo'

json.exception.out_of_range.405

The JSON Patch operations 'remove' and 'add' can not be applied to the root element of the JSON value.

Example message

JSON pointer has no parent

json.exception.out_of_range.406

A parsed number could not be stored as without changing it to NaN or INF.

Example message

number overflow parsing '10E1000'

json.exception.out_of_range.407

UBJSON and BSON only support integer numbers up to 9223372036854775807.

Example message

number overflow serializing '9223372036854775808'

json.exception.out_of_range.408

The size (following #) of an UBJSON array or object exceeds the maximal capacity.

Example message

excessive array size: 8658170730974374167

json.exception.out_of_range.409

Key identifiers to be serialized to BSON cannot contain code point U+0000, since the key is stored as zero-terminated c-string.

Example message

BSON key cannot contain code point U+0000 (at byte 2)

Further exceptions

This exception is thrown in case of errors that cannot be classified with the other exception types.

Exceptions have ids 5xx.

Example

The following code shows how an other_error exception can be caught.

#include <iostream>
#include <nlohmann/json.hpp>

using json = nlohmann::json;

int main()
{
    try
    {
        // executing a failing JSON Patch operation
        json value = R"({
            "best_biscuit": {
                "name": "Oreo"
            }
        })"_json;
        json patch = R"([{
            "op": "test",
            "path": "/best_biscuit/name",
            "value": "Choco Leibniz"
        }])"_json;
        value.patch(patch);
    }
    catch (json::other_error& e)
    {
        // output exception information
        std::cout << "message: " << e.what() << '\n'
                  << "exception id: " << e.id << std::endl;
    }
}

Output:

message: [json.exception.other_error.501] unsuccessful: {"op":"test","path":"/best_biscuit/name","value":"Choco Leibniz"}
exception id: 501

json.exception.other_error.501

A JSON Patch operation 'test' failed. The unsuccessful operation is also printed.

Example message

Executing {"op":"test", "path":"/baz", "value":"bar"} on {"baz": "qux"}:

[json.exception.other_error.501] unsuccessful: {"op":"test","path":"/baz","value":"bar"}