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@@ -114,13 +114,59 @@ Strong exception safety: if an exception occurs, the original value stays intact
|
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exceptions that can be thrown.
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```cpp
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--8<-- "examples/at__size_type.cpp"
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#include <iostream>
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#include <nlohmann/json.hpp>
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using json = nlohmann::json;
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int main()
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{
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// create JSON array
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json array = {"first", "2nd", "third", "fourth"};
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// output element at index 2 (third element)
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std::cout << array.at(2) << '\n';
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// change element at index 1 (second element) to "second"
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array.at(1) = "second";
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// output changed array
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std::cout << array << '\n';
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// exception type_error.304
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try
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{
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// use at() on a non-array type
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json str = "I am a string";
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str.at(0) = "Another string";
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}
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catch (const json::type_error& e)
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{
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std::cout << e.what() << '\n';
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}
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// exception out_of_range.401
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try
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{
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// try to write beyond the array limit
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array.at(5) = "sixth";
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}
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catch (const json::out_of_range& e)
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{
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std::cout << e.what() << '\n';
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}
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}
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```
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Output:
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```json
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--8<-- "examples/at__size_type.output"
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"third"
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["first","second","third","fourth"]
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[json.exception.type_error.304] cannot use at() with string
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[json.exception.out_of_range.401] array index 5 is out of range
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```
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??? example "Example: (1) access specified array element with bounds checking"
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@@ -129,13 +175,52 @@ Strong exception safety: if an exception occurs, the original value stays intact
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that can be thrown.
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```cpp
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--8<-- "examples/at__size_type_const.cpp"
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#include <iostream>
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#include <nlohmann/json.hpp>
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using json = nlohmann::json;
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int main()
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{
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// create JSON array
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const json array = {"first", "2nd", "third", "fourth"};
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// output element at index 2 (third element)
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std::cout << array.at(2) << '\n';
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// exception type_error.304
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try
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{
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// use at() on a non-array type
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const json str = "I am a string";
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std::cout << str.at(0) << '\n';
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}
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catch (const json::type_error& e)
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{
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std::cout << e.what() << '\n';
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}
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// exception out_of_range.401
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try
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{
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// try to read beyond the array limit
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std::cout << array.at(5) << '\n';
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}
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catch (const json::out_of_range& e)
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{
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std::cout << e.what() << '\n';
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}
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}
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```
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Output:
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```json
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--8<-- "examples/at__size_type_const.output"
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"third"
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[json.exception.type_error.304] cannot use at() with string
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[json.exception.out_of_range.401] array index 5 is out of range
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```
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??? example "Example: (2) access specified object element with bounds checking"
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@@ -144,13 +229,64 @@ Strong exception safety: if an exception occurs, the original value stays intact
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exceptions that can be thrown.
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|
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```cpp
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--8<-- "examples/at__object_t_key_type.cpp"
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#include <iostream>
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#include <nlohmann/json.hpp>
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using json = nlohmann::json;
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int main()
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{
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// create JSON object
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json object =
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{
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{"the good", "il buono"},
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{"the bad", "il cattivo"},
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{"the ugly", "il brutto"}
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};
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// output element with key "the ugly"
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std::cout << object.at("the ugly") << '\n';
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// change element with key "the bad"
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object.at("the bad") = "il cattivo";
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// output changed array
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std::cout << object << '\n';
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// exception type_error.304
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try
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{
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// use at() on a non-object type
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json str = "I am a string";
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str.at("the good") = "Another string";
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}
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catch (const json::type_error& e)
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{
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std::cout << e.what() << '\n';
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}
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// exception out_of_range.401
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try
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{
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// try to write at a nonexisting key
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object.at("the fast") = "il rapido";
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}
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catch (const json::out_of_range& e)
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{
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std::cout << e.what() << '\n';
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}
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}
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```
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Output:
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```json
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--8<-- "examples/at__object_t_key_type.output"
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"il brutto"
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{"the bad":"il cattivo","the good":"il buono","the ugly":"il brutto"}
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[json.exception.type_error.304] cannot use at() with string
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[json.exception.out_of_range.403] key 'the fast' not found
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```
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??? example "Example: (2) access specified object element with bounds checking"
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@@ -159,13 +295,57 @@ Strong exception safety: if an exception occurs, the original value stays intact
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||||
that can be thrown.
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||||
|
||||
```cpp
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--8<-- "examples/at__object_t_key_type_const.cpp"
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#include <iostream>
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#include <nlohmann/json.hpp>
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|
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using json = nlohmann::json;
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|
||||
int main()
|
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{
|
||||
// create JSON object
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const json object =
|
||||
{
|
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{"the good", "il buono"},
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{"the bad", "il cattivo"},
|
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{"the ugly", "il brutto"}
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};
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|
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// output element with key "the ugly"
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std::cout << object.at("the ugly") << '\n';
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||||
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||||
// exception type_error.304
|
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try
|
||||
{
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||||
// use at() on a non-object type
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const json str = "I am a string";
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||||
std::cout << str.at("the good") << '\n';
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}
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catch (const json::type_error& e)
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||||
{
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std::cout << e.what() << '\n';
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||||
}
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||||
|
||||
// exception out_of_range.401
|
||||
try
|
||||
{
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||||
// try to read from a nonexisting key
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||||
std::cout << object.at("the fast") << '\n';
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||||
}
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||||
catch (const json::out_of_range)
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||||
{
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||||
std::cout << "out of range" << '\n';
|
||||
}
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||||
}
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||||
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```
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||||
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Output:
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||||
|
||||
```json
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||||
--8<-- "examples/at__object_t_key_type_const.output"
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||||
"il brutto"
|
||||
[json.exception.type_error.304] cannot use at() with string
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||||
out of range
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||||
|
||||
```
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||||
|
||||
??? example "Example: (3) access specified object element using string_view with bounds checking"
|
||||
@@ -174,13 +354,66 @@ Strong exception safety: if an exception occurs, the original value stays intact
|
||||
exceptions that can be thrown.
|
||||
|
||||
```cpp
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||||
--8<-- "examples/at__keytype.c++17.cpp"
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||||
#include <iostream>
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||||
#include <string_view>
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||||
#include <nlohmann/json.hpp>
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||||
|
||||
using namespace std::string_view_literals;
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create JSON object
|
||||
json object =
|
||||
{
|
||||
{"the good", "il buono"},
|
||||
{"the bad", "il cattivo"},
|
||||
{"the ugly", "il brutto"}
|
||||
};
|
||||
|
||||
// output element with key "the ugly" using string_view
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||||
std::cout << object.at("the ugly"sv) << '\n';
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||||
|
||||
// change element with key "the bad" using string_view
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||||
object.at("the bad"sv) = "il cattivo";
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||||
|
||||
// output changed array
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||||
std::cout << object << '\n';
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||||
|
||||
// exception type_error.304
|
||||
try
|
||||
{
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||||
// use at() with string_view on a non-object type
|
||||
json str = "I am a string";
|
||||
str.at("the good"sv) = "Another string";
|
||||
}
|
||||
catch (const json::type_error& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
|
||||
// exception out_of_range.401
|
||||
try
|
||||
{
|
||||
// try to write at a nonexisting key using string_view
|
||||
object.at("the fast"sv) = "il rapido";
|
||||
}
|
||||
catch (const json::out_of_range& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
}
|
||||
|
||||
```
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||||
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Output:
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|
||||
```json
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||||
--8<-- "examples/at__keytype.c++17.output"
|
||||
"il brutto"
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{"the bad":"il cattivo","the good":"il buono","the ugly":"il brutto"}
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||||
[json.exception.type_error.304] cannot use at() with string
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||||
[json.exception.out_of_range.403] key 'the fast' not found
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||||
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||||
```
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||||
|
||||
??? example "Example: (3) access specified object element using string_view with bounds checking"
|
||||
@@ -189,13 +422,59 @@ Strong exception safety: if an exception occurs, the original value stays intact
|
||||
that can be thrown.
|
||||
|
||||
```cpp
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||||
--8<-- "examples/at__keytype_const.c++17.cpp"
|
||||
#include <iostream>
|
||||
#include <string_view>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using namespace std::string_view_literals;
|
||||
using json = nlohmann::json;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create JSON object
|
||||
const json object =
|
||||
{
|
||||
{"the good", "il buono"},
|
||||
{"the bad", "il cattivo"},
|
||||
{"the ugly", "il brutto"}
|
||||
};
|
||||
|
||||
// output element with key "the ugly" using string_view
|
||||
std::cout << object.at("the ugly"sv) << '\n';
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||||
|
||||
// exception type_error.304
|
||||
try
|
||||
{
|
||||
// use at() with string_view on a non-object type
|
||||
const json str = "I am a string";
|
||||
std::cout << str.at("the good"sv) << '\n';
|
||||
}
|
||||
catch (const json::type_error& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
|
||||
// exception out_of_range.401
|
||||
try
|
||||
{
|
||||
// try to read from a nonexisting key using string_view
|
||||
std::cout << object.at("the fast"sv) << '\n';
|
||||
}
|
||||
catch (const json::out_of_range& e)
|
||||
{
|
||||
std::cout << "out of range" << '\n';
|
||||
}
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/at__keytype_const.c++17.output"
|
||||
"il brutto"
|
||||
[json.exception.type_error.304] cannot use at() with string
|
||||
out of range
|
||||
|
||||
```
|
||||
|
||||
??? example "Example: (4) access specified element via JSON Pointer"
|
||||
@@ -204,13 +483,128 @@ Strong exception safety: if an exception occurs, the original value stays intact
|
||||
exceptions that can be thrown.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/at__json_pointer.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
using namespace nlohmann::literals;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create a JSON value
|
||||
json j =
|
||||
{
|
||||
{"number", 1}, {"string", "foo"}, {"array", {1, 2}}
|
||||
};
|
||||
|
||||
// read-only access
|
||||
|
||||
// output element with JSON pointer "/number"
|
||||
std::cout << j.at("/number"_json_pointer) << '\n';
|
||||
// output element with JSON pointer "/string"
|
||||
std::cout << j.at("/string"_json_pointer) << '\n';
|
||||
// output element with JSON pointer "/array"
|
||||
std::cout << j.at("/array"_json_pointer) << '\n';
|
||||
// output element with JSON pointer "/array/1"
|
||||
std::cout << j.at("/array/1"_json_pointer) << '\n';
|
||||
|
||||
// writing access
|
||||
|
||||
// change the string
|
||||
j.at("/string"_json_pointer) = "bar";
|
||||
// output the changed string
|
||||
std::cout << j["string"] << '\n';
|
||||
|
||||
// change an array element
|
||||
j.at("/array/1"_json_pointer) = 21;
|
||||
// output the changed array
|
||||
std::cout << j["array"] << '\n';
|
||||
|
||||
// out_of_range.106
|
||||
try
|
||||
{
|
||||
// try to use an array index with leading '0'
|
||||
json::reference ref = j.at("/array/01"_json_pointer);
|
||||
}
|
||||
catch (const json::parse_error& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
|
||||
// out_of_range.109
|
||||
try
|
||||
{
|
||||
// try to use an array index that is not a number
|
||||
json::reference ref = j.at("/array/one"_json_pointer);
|
||||
}
|
||||
catch (const json::parse_error& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
|
||||
// out_of_range.401
|
||||
try
|
||||
{
|
||||
// try to use an invalid array index
|
||||
json::reference ref = j.at("/array/4"_json_pointer);
|
||||
}
|
||||
catch (const json::out_of_range& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
|
||||
// out_of_range.402
|
||||
try
|
||||
{
|
||||
// try to use the array index '-'
|
||||
json::reference ref = j.at("/array/-"_json_pointer);
|
||||
}
|
||||
catch (const json::out_of_range& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
|
||||
// out_of_range.403
|
||||
try
|
||||
{
|
||||
// try to use a JSON pointer to a nonexistent object key
|
||||
json::const_reference ref = j.at("/foo"_json_pointer);
|
||||
}
|
||||
catch (const json::out_of_range& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
|
||||
// out_of_range.404
|
||||
try
|
||||
{
|
||||
// try to use a JSON pointer that cannot be resolved
|
||||
json::reference ref = j.at("/number/foo"_json_pointer);
|
||||
}
|
||||
catch (const json::out_of_range& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/at__json_pointer.output"
|
||||
1
|
||||
"foo"
|
||||
[1,2]
|
||||
2
|
||||
"bar"
|
||||
[1,21]
|
||||
[json.exception.parse_error.106] parse error: array index '01' must not begin with '0'
|
||||
[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'
|
||||
|
||||
```
|
||||
|
||||
??? example "Example: (4) access specified element via JSON Pointer"
|
||||
@@ -219,13 +613,102 @@ Strong exception safety: if an exception occurs, the original value stays intact
|
||||
that can be thrown.
|
||||
|
||||
```cpp
|
||||
--8<-- "examples/at__json_pointer_const.cpp"
|
||||
#include <iostream>
|
||||
#include <nlohmann/json.hpp>
|
||||
|
||||
using json = nlohmann::json;
|
||||
using namespace nlohmann::literals;
|
||||
|
||||
int main()
|
||||
{
|
||||
// create a JSON value
|
||||
const json j =
|
||||
{
|
||||
{"number", 1}, {"string", "foo"}, {"array", {1, 2}}
|
||||
};
|
||||
|
||||
// read-only access
|
||||
|
||||
// output element with JSON pointer "/number"
|
||||
std::cout << j.at("/number"_json_pointer) << '\n';
|
||||
// output element with JSON pointer "/string"
|
||||
std::cout << j.at("/string"_json_pointer) << '\n';
|
||||
// output element with JSON pointer "/array"
|
||||
std::cout << j.at("/array"_json_pointer) << '\n';
|
||||
// output element with JSON pointer "/array/1"
|
||||
std::cout << j.at("/array/1"_json_pointer) << '\n';
|
||||
|
||||
// out_of_range.109
|
||||
try
|
||||
{
|
||||
// try to use an array index that is not a number
|
||||
json::const_reference ref = j.at("/array/one"_json_pointer);
|
||||
}
|
||||
catch (const json::parse_error& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
|
||||
// out_of_range.401
|
||||
try
|
||||
{
|
||||
// try to use an invalid array index
|
||||
json::const_reference ref = j.at("/array/4"_json_pointer);
|
||||
}
|
||||
catch (const json::out_of_range& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
|
||||
// out_of_range.402
|
||||
try
|
||||
{
|
||||
// try to use the array index '-'
|
||||
json::const_reference ref = j.at("/array/-"_json_pointer);
|
||||
}
|
||||
catch (const json::out_of_range& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
|
||||
// out_of_range.403
|
||||
try
|
||||
{
|
||||
// try to use a JSON pointer to a nonexistent object key
|
||||
json::const_reference ref = j.at("/foo"_json_pointer);
|
||||
}
|
||||
catch (const json::out_of_range& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
|
||||
// out_of_range.404
|
||||
try
|
||||
{
|
||||
// try to use a JSON pointer that cannot be resolved
|
||||
json::const_reference ref = j.at("/number/foo"_json_pointer);
|
||||
}
|
||||
catch (const json::out_of_range& e)
|
||||
{
|
||||
std::cout << e.what() << '\n';
|
||||
}
|
||||
}
|
||||
|
||||
```
|
||||
|
||||
Output:
|
||||
|
||||
```json
|
||||
--8<-- "examples/at__json_pointer_const.output"
|
||||
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'
|
||||
|
||||
```
|
||||
|
||||
## See also
|
||||
@@ -241,4 +724,6 @@ Strong exception safety: if an exception occurs, the original value stays intact
|
||||
3. Added in version 3.11.0. Fixed in version 3.13.0 to consistently accept `std::string_view`-convertible keys, as
|
||||
already supported by [`operator[]`](operator[].md), [`value`](value.md), [`find`](find.md), and other lookup
|
||||
functions.
|
||||
4. Added in version 2.0.0.
|
||||
4. Added in version 2.0.0. Throws [`parse_error.109`](../../home/exceptions.md#jsonexceptionparse_error109) instead of
|
||||
[`out_of_range.404`](../../home/exceptions.md#jsonexceptionout_of_range404) for a one-character array index that is not
|
||||
a digit (e.g., `/x`) in version 3.13.0, as it already did for longer ones.
|
||||
Reference in new issue
Block a user