json/api/json_pointer/front/index.md

nlohmann::json_pointer::front

const string_t& front() const;

Return the first reference token.

Return value

First reference token.

Exception safety

Strong exception safety: if an exception occurs, the original value stays intact.

Exceptions

Throws out_of_range.405 if the JSON pointer has no parent.

Complexity

Constant.

Examples

Example

The example shows the usage of front.

#include <iostream>
#include <nlohmann/json.hpp>

using json = nlohmann::json;

int main()
{
    // different JSON Pointers
    json::json_pointer ptr1("/foo");
    json::json_pointer ptr2("/foo/0");

    // call empty()
    std::cout << "first reference token of \"" << ptr1 << "\" is \"" << ptr1.front() << "\"\n"
              << "first reference token of \"" << ptr2 << "\" is \"" << ptr2.front() << "\"" << std::endl;
}

Output:

first reference token of "/foo" is "foo"
first reference token of "/foo/0" is "foo"

See also

• back return last reference token
• pop_front remove the first reference token
• push_front append an unescaped token at the start of the pointer

Version history

• Added in version 3.13.0 unreleased.