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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 = int64_t, class NumberFloatType = double, template< typename U > class AllocatorType = std::allocator>
Returns the number of elements in a JSON value.
- Returns
- The return value depends on the different types and is defined as follows:
Value type | return value |
null | 0 |
boolean | 1 |
string | 1 |
number | 1 |
object | result of function object_t::size() |
array | result of function array_t::size() |
- Complexity
- Constant, as long as array_t and object_t satisfy the Container concept; that is, their size() functions have constant complexity.
- Requirements
- This function satisfies the Container requirements:
- The complexity is constant.
- Has the semantics of
std::distance(begin(), end()) .
- Example
- The following code calls size on the different value types.
10 json j_number_integer = 17; 11 json j_number_float = 23.42; 12 json j_object = {{ "one", 1}, { "two", 2}}; 14 json j_array = {1, 2, 4, 8, 16}; 16 json j_string = "Hello, world"; 19 std::cout << j_null. size() << '\n'; 20 std::cout << j_boolean. size() << '\n'; 21 std::cout << j_number_integer. size() << '\n'; 22 std::cout << j_number_float. size() << '\n'; 23 std::cout << j_object. size() << '\n'; 24 std::cout << j_object_empty.size() << '\n'; 25 std::cout << j_array. size() << '\n'; 26 std::cout << j_array_empty.size() << '\n'; 27 std::cout << j_string. size() << '\n'; a class to store JSON values
object (unordered set of name/value pairs)
namespace for Niels Lohmann
array (ordered collection of values)
size_type size() const noexcept returns the number of elements
Output (play with this example online): 0
1
1
1
2
0
5
0
1
The example code above can be translated withg++ -std=c++11 -Isrc doc/examples/size.cpp -o size
- Since
- version 1.0.0
Definition at line 4107 of file json.hpp.
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