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◆ at() [2/6]
Returns a const reference to the element at with specified JSON pointer ptr, with bounds checking.
- Parameters
-
[in] | ptr | JSON pointer to the desired element |
- Returns
- reference to the element pointed to by ptr
- Exceptions
-
parse_error.106 | if an array index in the passed JSON pointer ptr begins with '0'. See example below. |
parse_error.109 | if an array index in the passed JSON pointer ptr is not a number. See example below. |
out_of_range.401 | if an array index in the passed JSON pointer ptr is out of range. See example below. |
out_of_range.402 | if the array index '-' is used in the passed JSON pointer ptr. As at provides checked access (and no elements are implicitly inserted), the index '-' is always invalid. See example below. |
out_of_range.403 | if the JSON pointer describes a key of an object which cannot be found. See example below. |
out_of_range.404 | if the JSON pointer ptr can not be resolved. See example below. |
- Exception safety
- Strong guarantee: if an exception is thrown, there are no changes in the JSON value.
- Complexity
- Constant.
- Since
- version 2.0.0
- Example
- The behavior is shown in the example.
2 #include <nlohmann/json.hpp>
11 { "number", 1}, { "string", "foo"}, { "array", {1, 2}}
17 std::cout << j.at( "/number"_json_pointer) << '\n';
19 std::cout << j.at( "/string"_json_pointer) << '\n';
21 std::cout << j.at( "/array"_json_pointer) << '\n';
23 std::cout << j.at( "/array/1"_json_pointer) << '\n';
33 std::cout << e.what() << '\n';
44 std::cout << e.what() << '\n';
55 std::cout << e.what() << '\n';
66 std::cout << e.what() << '\n';
77 std::cout << e.what() << '\n';
Output (play with this example online): 1
"foo"
[1,2]
2
[json.exception.parse_error.109] parse error: array index 'one' is not a number
[json.exception.out_of_range.401] array index 4 is out of range
[json.exception.out_of_range.402] array index '-' (2) is out of range
[json.exception.out_of_range.403] key 'foo' not found
[json.exception.out_of_range.404] unresolved reference token 'foo'
The example code above can be translated withg++ -std=c++11 -Isingle_include doc/examples/at_json_pointer_const.cpp -o at_json_pointer_const
Definition at line 21995 of file json.hpp.
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