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<span class=w> </span><span class=nt>&quot;active&quot;</span><span class=p>:</span><span class=w> </span><span class=kc>true</span><span class=p>,</span>
<span class=w> </span><span class=nt>&quot;name&quot;</span><span class=p>:</span><span class=w> </span><span class=p>{</span><span class=nt>&quot;de&quot;</span><span class=p>:</span><span class=w> </span><span class=s2>&quot;Maus&quot;</span><span class=p>,</span><span class=w> </span><span class=nt>&quot;en&quot;</span><span class=p>:</span><span class=w> </span><span class=s2>&quot;mouse&quot;</span><span class=p>,</span><span class=w> </span><span class=nt>&quot;es&quot;</span><span class=p>:</span><span class=w> </span><span class=s2>&quot;ratón&quot;</span><span class=p>}</span>
<span class=p>}</span>
</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../insert/ >insert</a> add values to an array/object</li> <li><a href=../merge_patch/ >merge_patch</a> applies a <abbr title="JavaScript Object Notation">JSON</abbr> Merge Patch</li> <li><a href=../../../features/modifying_values/ >Modifying values</a> - the article on modifying values</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.0.0.</li> <li>Added <code>merge_objects</code> parameter in 3.10.5.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 4, 2026 09:13:25 UTC">July 4, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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</code></pre></div> </details> <h2 id=see-also>See also<a class=headerlink href=#see-also title="Permanent link">&para;</a></h2> <ul> <li><a href=../insert/ >insert</a> add values to an array/object</li> <li><a href=../merge_patch/ >merge_patch</a> applies a <abbr title="JavaScript Object Notation">JSON</abbr> Merge Patch</li> <li><a href=../../../features/modifying_values/ >Modifying values</a> - the article on modifying values</li> </ul> <h2 id=version-history>Version history<a class=headerlink href=#version-history title="Permanent link">&para;</a></h2> <ul> <li>Added in version 3.0.0.</li> <li>Added <code>merge_objects</code> parameter in 3.10.5.</li> </ul> <!-- https://squidfunk.github.io/mkdocs-material/reference/tooltips/#adding-a-glossary --> <aside class=md-source-file> <span class=md-source-file__fact> <span class=md-icon title="Last update"> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M21 13.1c-.1 0-.3.1-.4.2l-1 1 2.1 2.1 1-1c.2-.2.2-.6 0-.8l-1.3-1.3c-.1-.1-.2-.2-.4-.2m-1.9 1.8-6.1 6V23h2.1l6.1-6.1zM12.5 7v5.2l4 2.4-1 1L11 13V7zM11 21.9c-5.1-.5-9-4.8-9-9.9C2 6.5 6.5 2 12 2c5.3 0 9.6 4.1 10 9.3-.3-.1-.6-.2-1-.2s-.7.1-1 .2C19.6 7.2 16.2 4 12 4c-4.4 0-8 3.6-8 8 0 4.1 3.1 7.5 7.1 7.9l-.1.2z"/></svg> </span> <span class="git-revision-date-localized-plugin git-revision-date-localized-plugin-date" title="July 8, 2026 18:18:24 UTC">July 8, 2026</span> </span> </aside> </article> </div> <script>var tabs=__md_get("__tabs");if(Array.isArray(tabs))e:for(var set of document.querySelectorAll(".tabbed-set")){var labels=set.querySelector(".tabbed-labels");for(var tab of tabs)for(var label of labels.getElementsByTagName("label"))if(label.innerText.trim()===tab){var input=document.getElementById(label.htmlFor);input.checked=!0;continue e}}</script> <script>var target=document.getElementById(location.hash.slice(1));target&&target.name&&(target.checked=target.name.startsWith("__tabbed_"))</script> </div> <button type=button class="md-top md-icon" data-md-component=top hidden> <svg xmlns=http://www.w3.org/2000/svg viewbox="0 0 24 24"><path d="M13 20h-2V8l-5.5 5.5-1.42-1.42L12 4.16l7.92 7.92-1.42 1.42L13 8z"/></svg> Back to top </button> </main> <footer class=md-footer> <div class="md-footer-meta md-typeset"> <div class="md-footer-meta__inner md-grid"> <div class=md-copyright> <div class=md-copyright__highlight> Copyright &copy; 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api/basic_json/update/index.md
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# nlohmann::basic_json::update
```
// (1)
void update(const_reference j, bool merge_objects = false);
// (2)
void update(const_iterator first, const_iterator last, bool merge_objects = false);
```
1. Inserts all values from JSON object `j`.
1. Inserts all values from range `[first, last)`
When `merge_objects` is `false` (default), existing keys are overwritten. When `merge_objects` is `true`, recursively merges objects with common keys.
If the JSON value is `null`, it is implicitly converted to an empty object before the values are inserted.
The function is motivated by Python's [dict.update](https://docs.python.org/3.6/library/stdtypes.html#dict.update) function.
## Iterator invalidation
For [`ordered_json`](https://json.nlohmann.me/api/ordered_json/index.md), adding a value to an object can yield a reallocation, in which case all iterators (including the `end()` iterator) and all references to the elements are invalidated.
## Parameters
`j` (in) : JSON object to read values from
`merge_objects` (in) : when `true`, keys that exist in both objects and whose value in the source is itself an object are merged recursively; all other values are overwritten as usual (default: `false`)
`first` (in) : the beginning of the range of elements to insert
`last` (in) : the end of the range of elements to insert
## Exception safety
Basic guarantee: if an exception is thrown during the operation, the JSON value may be partially modified.
## Exceptions
1. The function can throw the following exceptions:
- Throws [`type_error.312`](https://json.nlohmann.me/home/exceptions/#jsonexceptiontype_error312) if called on JSON values other than objects; example: `"cannot use update() with string"`
1. The function can throw the following exceptions:
- Throws [`type_error.312`](https://json.nlohmann.me/home/exceptions/#jsonexceptiontype_error312) if called on JSON values other than objects; example: `"cannot use update() with string"`
- Throws [`invalid_iterator.210`](https://json.nlohmann.me/home/exceptions/#jsonexceptioninvalid_iterator210) if `first` and `last` do not belong to the same JSON value; example: `"iterators do not fit"`
## Complexity
1. O(N\*log(size() + N)), where N is the number of elements to insert.
1. O(N\*log(size() + N)), where N is the number of elements to insert.
## Examples
Example
The example shows how `update()` is used.
```
#include <iostream>
#include <iomanip>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using namespace nlohmann::literals;
int main()
{
// create two JSON objects
json o1 = R"( {"color": "red", "price": 17.99, "names": {"de": "Flugzeug"}} )"_json;
json o2 = R"( {"color": "blue", "speed": 100, "names": {"en": "plane"}} )"_json;
json o3 = o1;
// add all keys from o2 to o1 (updating "color", replacing "names")
o1.update(o2);
// add all keys from o2 to o1 (updating "color", merging "names")
o3.update(o2, true);
// output updated object o1 and o3
std::cout << std::setw(2) << o1 << '\n';
std::cout << std::setw(2) << o3 << '\n';
}
```
Output:
```
{
"color": "blue",
"names": {
"en": "plane"
},
"price": 17.99,
"speed": 100
}
{
"color": "blue",
"names": {
"de": "Flugzeug",
"en": "plane"
},
"price": 17.99,
"speed": 100
}
```
Example
The example shows how `update()` is used.
```
#include <iostream>
#include <iomanip>
#include <nlohmann/json.hpp>
using json = nlohmann::json;
using namespace nlohmann::literals;
int main()
{
// create two JSON objects
json o1 = R"( {"color": "red", "price": 17.99, "names": {"de": "Flugzeug"}} )"_json;
json o2 = R"( {"color": "blue", "speed": 100, "names": {"en": "plane"}} )"_json;
json o3 = o1;
// add all keys from o2 to o1 (updating "color", replacing "names")
o1.update(o2.begin(), o2.end());
// add all keys from o2 to o1 (updating "color", merging "names")
o3.update(o2.begin(), o2.end(), true);
// output updated object o1 and o3
std::cout << std::setw(2) << o1 << '\n';
std::cout << std::setw(2) << o3 << '\n';
}
```
Output:
```
{
"color": "blue",
"names": {
"en": "plane"
},
"price": 17.99,
"speed": 100
}
{
"color": "blue",
"names": {
"de": "Flugzeug",
"en": "plane"
},
"price": 17.99,
"speed": 100
}
```
Example
One common use case for this function is the handling of user settings. Assume your application can be configured in some aspects:
```
{
"color": "red",
"active": true,
"name": {"de": "Maus", "en": "mouse"}
}
```
The user may override the default settings selectively:
```
{
"color": "blue",
"name": {"es": "ratón"},
}
```
Then `update` manages the merging of default settings and user settings:
```
auto user_settings = json::parse("config.json");
auto effective_settings = get_default_settings();
effective_settings.update(user_settings);
```
Now `effective_settings` contains the default settings, but those keys set by the user are overwritten:
```
{
"color": "blue",
"active": true,
"name": {"es": "ratón"}
}
```
Note existing keys were just overwritten. To merge objects, `merge_objects` setting should be set to `true`:
```
auto user_settings = json::parse("config.json");
auto effective_settings = get_default_settings();
effective_settings.update(user_settings, true);
```
```
{
"color": "blue",
"active": true,
"name": {"de": "Maus", "en": "mouse", "es": "ratón"}
}
```
## See also
- [insert](https://json.nlohmann.me/api/basic_json/insert/index.md) add values to an array/object
- [merge_patch](https://json.nlohmann.me/api/basic_json/merge_patch/index.md) applies a JSON Merge Patch
- [Modifying values](https://json.nlohmann.me/features/modifying_values/index.md) - the article on modifying values
## Version history
- Added in version 3.0.0.
- Added `merge_objects` parameter in 3.10.5.