front() [1/2]

template<template< typename U, typename V, typename... Args > class ObjectType = std::map, template< typename U, typename... Args > class ArrayType = std::vector, class StringType = std::string, class BooleanType = bool, class NumberIntegerType = std::int64_t, class NumberUnsignedType = std::uint64_t, class NumberFloatType = double, template< typename U > class AllocatorType = std::allocator, template< typename T, typename SFINAE=void > class JSONSerializer = adl_serializer, class BinaryType = std::vector<std::uint8_t>>

reference nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType >::front ( )

inline

access the first element

Returns a reference to the first element in the container. For a JSON container c, the expression c.front() is equivalent to *c.begin().

Returns

In case of a structured type (array or object), a reference to the first element is returned. In case of number, string, boolean, or binary values, a reference to the value is returned.

@complexity Constant.

Precondition

The JSON value must not be null (would throw std::out_of_range) or an empty array or object (undefined behavior, guarded by assertions).

Postcondition

The JSON value remains unchanged.

Exceptions

invalid_iterator.214

when called on null value

@liveexample{The following code shows an example for front().,front}

See also

see back() – access the last element

Since

version 1.0.0

Definition at line 21809 of file json.hpp.

    {
        return *begin();
    }