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◆ front() [2/2]
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>
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\n 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
-
std::out_of_range | when called on null value |
- Example\n The following code shows an example for
front() . \n @includelineno front.cpp \n Output (play with this example @htmlinclude front.link):\n @verbinclude front.output \n The example code above can be translated with @verbatim g++ -std=c++11 -Isrc doc/examples/front.cpp -o front @endverbatim
- See also
- back() – access the last element
- Since
- version 1.0.0
Definition at line 4200 of file json.hpp.
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