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>
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, or boolean 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 |
- Example^^ The following code shows an example for front(). ^^ front.cpp
- Output (play with this example online):^^
true
17
23.42
1
1
"Hello, world"
^^ The example code above can be translated withg++ -std=c++11 -Isingle_include doc/examples/front.cpp -o front
- See also
- back() – access the last element
- Since
- version 1.0.0
Definition at line 15914 of file json.hpp.