json/docs/mkdocs/docs/api/basic_json/exception.md

nlohmann::basic_json::exception

class exception : public std::exception;

This class is an extension of std::exception objects with a member id for exception ids. 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, see example below.

classDiagram
  direction LR
  
    class std_exception ["std::exception"] {
        <<interface>>
    }

    class json_exception ["basic_json::exception"] {
        +const int id
        +const char* what() const
    }
    
    class json_parse_error ["basic_json::parse_error"] {
        +const std::size_t byte
    }

    class json_invalid_iterator ["basic_json::invalid_iterator"]
    class json_type_error ["basic_json::type_error"]
    class json_out_of_range ["basic_json::out_of_range"]
    class json_other_error ["basic_json::other_error"]

    std_exception <|-- json_exception
    json_exception <|-- json_parse_error
    json_exception <|-- json_invalid_iterator
    json_exception <|-- json_type_error
    json_exception <|-- json_out_of_range
    json_exception <|-- json_other_error

    style json_exception fill:#CCCCFF

Class hierarchy of the library's exceptions; arrows point from a derived class to its base class, and the highlighted box is `basic_json::exception`.

Subclasses:

• parse_error for exceptions indicating a parse error
• invalid_iterator for exceptions indicating errors with iterators
• type_error for exceptions indicating executing a member function with a wrong type
• out_of_range for exceptions indicating access out of the defined range
• other_error for exceptions indicating other library errors

Member functions

• what - returns explanatory string

Member variables

• id - the id of the exception

Notes

To have nothrow-copy-constructible exceptions, we internally use std::runtime_error which can cope with arbitrary-length error messages. Intermediate strings are built with static functions and then passed to the actual constructor.

Examples

??? example

The following code shows how arbitrary library exceptions can be caught.

```cpp
--8<-- "examples/exception.cpp"
```

Output:

```json
--8<-- "examples/exception.output"
```

See also

• List of exceptions - overview of all exceptions thrown by the library
• Working Without Exceptions - using the library without exceptions
• JSON_DIAGNOSTICS - extended exception messages with the path of the failing value
• Parsing and Exceptions - parsing alternatives that do not throw
• Debugging - debugging aids

Version history

• Added in version 3.0.0.