JSON for Modern C++ 3.9.1

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accept
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basic_json
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~basic_json
| ## ◆ contains() [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>>
bool nlohmann::basic_json< ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType >::contains | ( | const json_pointer & | ptr | ) | const
| inline
  Check whether the given JSON pointer ptr can be resolved in the current JSON value. Note This method can be executed on any JSON value type. Parameters
  [in] | ptr | JSON pointer to check its existence.
  Returns true if the JSON pointer can be resolved to a stored value, false otherwise. Postcondition If `j.contains(ptr)` returns true, it is safe to call `j[ptr]`. Exceptions
  parse_error.106 | if an array index begins with '0'
  parse_error.109 | if an array index was not a number
  Complexity Logarithmic in the size of the JSON object. Example The following code shows an example for `contains()`. 1 #include <iostream> 2 #include <nlohmann/json.hpp> 3 4 using json = nlohmann::json; 5 6 int main() 7 { 8 // create a JSON value 9 json j = 10 { 11 {"number", 1}, {"string", "foo"}, {"array", {1, 2}} 12 }; 13 14 std::cout << std::boolalpha 15 << j.contains("/number"_json_pointer) << '\n' 16 << j.contains("/string"_json_pointer) << '\n' 17 << j.contains("/array"_json_pointer) << '\n' 18 << j.contains("/array/1"_json_pointer) << '\n' 19 << j.contains("/array/-"_json_pointer) << '\n' 20 << j.contains("/array/4"_json_pointer) << '\n' 21 << j.contains("/baz"_json_pointer) << std::endl; 22 23 try 24 { 25 // try to use an array index with leading '0' 26 j.contains("/array/01"_json_pointer); 27 } 28 catch (json::parse_error& e) 29 { 30 std::cout << e.what() << '\n'; 31 } 32 33 try 34 { 35 // try to use an array index that is not a number 36 j.contains("/array/one"_json_pointer); 37 } 38 catch (json::parse_error& e) 39 { 40 std::cout << e.what() << '\n'; 41 } 42 } Output (play with this example online):
      true
      true
      true
      true
      false
      false
      false
  The example code above can be translated with
      g++ -std=c++11 -Isingle_include doc/examples/contains_json_pointer.cpp -o contains_json_pointer
See also contains(KeyT &&) const – checks the existence of a key Since version 3.7.0 Definition at line 20960 of file json.hpp.

nlohmann::basic_json::parse_error
detail::parse_error parse_error
exception indicating a parse error
Definition: json.hpp:16762
nlohmann::json
basic_json<> json
default JSON class
Definition: json.hpp:2940