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api/basic_json/parse.md
+433 -18
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@@ -119,13 +119,63 @@ outside of a string, invalid) byte; see the [FAQ entry](../../home/faq.md#nul-by
The example below demonstrates the `parse()` function reading from an array.
```cpp
--8<-- "examples/parse__array__parser_callback_t.cpp"
#include <iostream>
#include <iomanip>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
int main()
{
// a JSON text
char text[] = R"(
{
"Image": {
"Width": 800,
"Height": 600,
"Title": "View from 15th Floor",
"Thumbnail": {
"Url": "http://www.example.com/image/481989943",
"Height": 125,
"Width": 100
},
"Animated" : false,
"IDs": [116, 943, 234, 38793]
}
}
)";
// parse and serialize JSON
json j_complete = json::parse(text);
std::cout << std::setw(4) << j_complete << "\n\n";
}
```
Output:
```json
--8<-- "examples/parse__array__parser_callback_t.output"
{
"Image": {
"Animated": false,
"Height": 600,
"IDs": [
116,
943,
234,
38793
],
"Thumbnail": {
"Height": 125,
"Url": "http://www.example.com/image/481989943",
"Width": 100
},
"Title": "View from 15th Floor",
"Width": 800
}
}
```
??? example "Example: (1) parse from a string"
@@ -133,13 +183,95 @@ outside of a string, invalid) byte; see the [FAQ entry](../../home/faq.md#nul-by
The example below demonstrates the `parse()` function with and without callback function.
```cpp
--8<-- "examples/parse__string__parser_callback_t.cpp"
#include <iostream>
#include <iomanip>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
int main()
{
// a JSON text
auto text = R"(
{
"Image": {
"Width": 800,
"Height": 600,
"Title": "View from 15th Floor",
"Thumbnail": {
"Url": "http://www.example.com/image/481989943",
"Height": 125,
"Width": 100
},
"Animated" : false,
"IDs": [116, 943, 234, 38793]
}
}
)";
// parse and serialize JSON
json j_complete = json::parse(text);
std::cout << std::setw(4) << j_complete << "\n\n";
// define parser callback
json::parser_callback_t cb = [](int depth, json::parse_event_t event, json & parsed)
{
// skip object elements with key "Thumbnail"
if (event == json::parse_event_t::key and parsed == json("Thumbnail"))
{
return false;
}
else
{
return true;
}
};
// parse (with callback) and serialize JSON
json j_filtered = json::parse(text, cb);
std::cout << std::setw(4) << j_filtered << '\n';
}
```
Output:
```json
--8<-- "examples/parse__string__parser_callback_t.output"
{
"Image": {
"Animated": false,
"Height": 600,
"IDs": [
116,
943,
234,
38793
],
"Thumbnail": {
"Height": 125,
"Url": "http://www.example.com/image/481989943",
"Width": 100
},
"Title": "View from 15th Floor",
"Width": 800
}
}
{
"Image": {
"Animated": false,
"Height": 600,
"IDs": [
116,
943,
234,
38793
],
"Title": "View from 15th Floor",
"Width": 800
}
}
```
??? example "Example: (1) parse from an input stream"
@@ -147,13 +279,103 @@ outside of a string, invalid) byte; see the [FAQ entry](../../home/faq.md#nul-by
The example below demonstrates the `parse()` function with and without callback function.
```cpp
--8<-- "examples/parse__istream__parser_callback_t.cpp"
#include <iostream>
#include <iomanip>
#include <sstream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
int main()
{
// a JSON text
auto text = R"(
{
"Image": {
"Width": 800,
"Height": 600,
"Title": "View from 15th Floor",
"Thumbnail": {
"Url": "http://www.example.com/image/481989943",
"Height": 125,
"Width": 100
},
"Animated" : false,
"IDs": [116, 943, 234, 38793]
}
}
)";
// fill a stream with JSON text
std::stringstream ss;
ss << text;
// parse and serialize JSON
json j_complete = json::parse(ss);
std::cout << std::setw(4) << j_complete << "\n\n";
// define parser callback
json::parser_callback_t cb = [](int depth, json::parse_event_t event, json & parsed)
{
// skip object elements with key "Thumbnail"
if (event == json::parse_event_t::key and parsed == json("Thumbnail"))
{
return false;
}
else
{
return true;
}
};
// fill a stream with JSON text
ss.clear();
ss << text;
// parse (with callback) and serialize JSON
json j_filtered = json::parse(ss, cb);
std::cout << std::setw(4) << j_filtered << '\n';
}
```
Output:
```json
--8<-- "examples/parse__istream__parser_callback_t.output"
{
"Image": {
"Animated": false,
"Height": 600,
"IDs": [
116,
943,
234,
38793
],
"Thumbnail": {
"Height": 125,
"Url": "http://www.example.com/image/481989943",
"Width": 100
},
"Title": "View from 15th Floor",
"Width": 800
}
}
{
"Image": {
"Animated": false,
"Height": 600,
"IDs": [
116,
943,
234,
38793
],
"Title": "View from 15th Floor",
"Width": 800
}
}
```
??? example "Example: (1) parse from a contiguous container"
@@ -161,13 +383,34 @@ outside of a string, invalid) byte; see the [FAQ entry](../../home/faq.md#nul-by
The example below demonstrates the `parse()` function reading from a contiguous container.
```cpp
--8<-- "examples/parse__contiguouscontainer__parser_callback_t.cpp"
#include <iostream>
#include <iomanip>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
int main()
{
// a JSON text given as std::vector
std::vector<std::uint8_t> text = {'[', '1', ',', '2', ',', '3', ']', '\0'};
// parse and serialize JSON
json j_complete = json::parse(text);
std::cout << std::setw(4) << j_complete << "\n\n";
}
```
Output:
```json
--8<-- "examples/parse__contiguouscontainer__parser_callback_t.output"
[
1,
2,
3
]
```
??? example "Example: (2) parse from a non-null-terminated string"
@@ -175,13 +418,34 @@ outside of a string, invalid) byte; see the [FAQ entry](../../home/faq.md#nul-by
The example below demonstrates the `parse()` function reading from a string that is not null-terminated.
```cpp
--8<-- "examples/parse__pointers.cpp"
#include <iostream>
#include <iomanip>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
int main()
{
// a JSON text given as string that is not null-terminated
const char* ptr = "[1,2,3]another value";
// parse and serialize JSON
json j_complete = json::parse(ptr, ptr + 7);
std::cout << std::setw(4) << j_complete << "\n\n";
}
```
Output:
```json
--8<-- "examples/parse__pointers.output"
[
1,
2,
3
]
```
??? example "Example: (2) parse from an iterator pair"
@@ -189,13 +453,34 @@ outside of a string, invalid) byte; see the [FAQ entry](../../home/faq.md#nul-by
The example below demonstrates the `parse()` function reading from an iterator pair.
```cpp
--8<-- "examples/parse__iterator_pair.cpp"
#include <iostream>
#include <iomanip>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
int main()
{
// a JSON text given an input with other values
std::vector<std::uint8_t> input = {'[', '1', ',', '2', ',', '3', ']', 'o', 't', 'h', 'e', 'r'};
// parse and serialize JSON
json j_complete = json::parse(input.begin(), input.begin() + 7);
std::cout << std::setw(4) << j_complete << "\n\n";
}
```
Output:
```json
--8<-- "examples/parse__iterator_pair.output"
[
1,
2,
3
]
```
??? example "Example: effect of `allow_exceptions` parameter"
@@ -203,13 +488,51 @@ outside of a string, invalid) byte; see the [FAQ entry](../../home/faq.md#nul-by
The example below demonstrates the effect of the `allow_exceptions` parameter in the `parse()` function.
```cpp
--8<-- "examples/parse__allow_exceptions.cpp"
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
int main()
{
// an invalid JSON text
std::string text = R"(
{
"key": "value without closing quotes
}
)";
// parse with exceptions
try
{
json j = json::parse(text);
}
catch (const json::parse_error& e)
{
std::cout << e.what() << std::endl;
}
// parse without exceptions
json j = json::parse(text, nullptr, false);
if (j.is_discarded())
{
std::cout << "the input is invalid JSON" << std::endl;
}
else
{
std::cout << "the input is valid JSON: " << j << std::endl;
}
}
```
Output:
```json
--8<-- "examples/parse__allow_exceptions.output"
[json.exception.parse_error.101] parse error at line 4, column 0: syntax error while parsing value - invalid string: control character U+000A (LF) must be escaped to \u000A or \n; last read: '"value without closing quotes<U+000A>'
the input is invalid JSON
```
??? example "Example: effect of `ignore_comments` parameter"
@@ -217,13 +540,56 @@ outside of a string, invalid) byte; see the [FAQ entry](../../home/faq.md#nul-by
The example below demonstrates the effect of the `ignore_comments` parameter in the `parse()` function.
```cpp
--8<-- "examples/comments.cpp"
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
int main()
{
std::string s = R"(
{
// update in 2006: removed Pluto
"planets": ["Mercury", "Venus", "Earth", "Mars",
"Jupiter", "Uranus", "Neptune" /*, "Pluto" */]
}
)";
try
{
json j = json::parse(s);
}
catch (json::exception& e)
{
std::cout << e.what() << std::endl;
}
json j = json::parse(s,
/* callback */ nullptr,
/* allow exceptions */ true,
/* ignore_comments */ true);
std::cout << j.dump(2) << '\n';
}
```
Output:
```
--8<-- "examples/comments.output"
[json.exception.parse_error.101] parse error at line 3, column 9: syntax error while parsing object key - invalid literal; last read: '<U+000A> {<U+000A> /'; expected string literal
{
"planets": [
"Mercury",
"Venus",
"Earth",
"Mars",
"Jupiter",
"Uranus",
"Neptune"
]
}
```
??? example "Example: effect of `ignore_trailing_commas` parameter"
@@ -231,13 +597,62 @@ outside of a string, invalid) byte; see the [FAQ entry](../../home/faq.md#nul-by
The example below demonstrates the effect of the `ignore_trailing_commas` parameter in the `parse()` function.
```cpp
--8<-- "examples/trailing_commas.cpp"
#include <iostream>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
int main()
{
std::string s = R"(
{
"planets": [
"Mercury",
"Venus",
"Earth",
"Mars",
"Jupiter",
"Uranus",
"Neptune",
]
}
)";
try
{
json j = json::parse(s);
}
catch (json::exception& e)
{
std::cout << e.what() << std::endl;
}
json j = json::parse(s,
/* callback */ nullptr,
/* allow exceptions */ true,
/* ignore_comments */ false,
/* ignore_trailing_commas */ true);
std::cout << j.dump(2) << '\n';
}
```
Output:
```
--8<-- "examples/trailing_commas.output"
[json.exception.parse_error.101] parse error at line 11, column 9: syntax error while parsing value - unexpected ']'; expected '[', '{', or a literal
{
"planets": [
"Mercury",
"Venus",
"Earth",
"Mars",
"Jupiter",
"Uranus",
"Neptune"
]
}
```
## See also