# Query Strings - Crow

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# Query Strings

A query string is the part of the url that comes after a `?` character, it is usually formatted as `key=value&otherkey=othervalue`.

Crow supports query strings through `crow::request::url_params`. The object is of type `crow::query_string` and can has the following functions:

## get(name)

Returns the value (as char*) based on the given key (or name). Returns `nullptr` if the key is not found.

## pop(name)

Works the same as `get`, but removes the returned value.

Note

`crow::request::url_params` is a const value, therefore for pop (also pop_list and pop_dict) to work, a copy needs to be made.

## get_list(name)

A url can be `http://example.com?key[]=value1&key[]=value2&key[]=value3`. Using `get_list("key")` on such a url returns an `std::vector<std::string>` containing `[value1, value2, value3]`.

`get_list("key", false)` can be used to parse `http://example.com?key=value1&key=value2&key=value3`

## pop_list(name)

Works the same as `get_list` but removes all instances of values having the given key (`use_brackets` is also available here).

## get_dict(name)

Returns an `std::unordered_map<std::string, std::string>` from a query string such as `?key[sub_key1]=value1&key[sub_key2]=value2&key[sub_key3]=value3`.
The key in the map is what's in the brackets (`sub_key1` for example), and the value being what's after the `=` sign (`value1`). The name passed to the function is not part of the returned value.

## pop_dict(name)

Works the same as `get_dict` but removing the values from the query string.

Warning

if your query string contains both a list and dictionary with the same key, it is best to use `pop_list` before either `get_dict` or `pop_dict`, since a map cannot contain more than one value per key, each item in the list will override the previous and only the last will remain with an empty key.

For more information take a look here.