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# basic_json::invalid_iterator

    class invalid_iterator : public exception;

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

Exceptions have ids 2xx.

## Member functions

- what - returns explanatory string

## Member variables

- id - the id of the exception

## Example

Example

The following code shows how a `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

## Version history

- Since version 3.0.0.