nlohmann::json_pointer::operator!=

// until C++20
template<typename RefStringTypeLhs, typename RefStringTypeRhs>
bool operator!=(
    const json_pointer<RefStringTypeLhs>& lhs,
    const json_pointer<RefStringTypeRhs>& rhs) noexcept;  // (1)

template<typename RefStringTypeLhs, typename StringType>
bool operator!=(
    const json_pointer<RefStringTypeLhs>& lhs,
    const StringType& rhs);                               // (2)

template<typename RefStringTypeRhs, typename StringType>
bool operator!=(
    const StringType& lhs,
    const json_pointer<RefStringTypeRhs>& rhs);           // (2)

1. Compares two JSON pointers for inequality by comparing their reference tokens.
2. Compares a JSON pointer and a string or a string and a JSON pointer for inequality by converting the string to a JSON pointer and comparing the JSON pointers according to 1.

Template parameters

RefStringTypeLhs, RefStringTypeRhs : the string type of the left-hand side or right-hand side JSON pointer, respectively

StringType : the string type derived from the json_pointer operand (json_pointer::string_t)

Parameters

lhs (in) : first value to consider

rhs (in) : second value to consider

Return value

whether the values lhs/*this and rhs are not equal

Exception safety

1. No-throw guarantee: this function never throws exceptions.
2. Strong exception safety: if an exception occurs, the original value stays intact.

Exceptions

1. (none)
2. The function can throw the following exceptions:
3. Throws parse_error.107 if the given JSON pointer s is nonempty and does not begin with a slash (/); see example below.
4. Throws parse_error.108 if a tilde (~) in the given JSON pointer s is not followed by 0 (representing ~) or 1 (representing /); see example below.

Complexity

Constant if lhs and rhs differ in the number of reference tokens, otherwise linear in the number of reference tokens.

Notes

Operator overload resolution

Since C++20 overload resolution will consider the rewritten candidate generated from operator==.

Deprecation

Overload 2 is deprecated and will be removed in a future major version release.

Examples

Example: (1) Comparing JSON pointers

The example demonstrates comparing JSON pointers.

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

using json = nlohmann::json;

int main()
{
    // different JSON pointers
    json::json_pointer ptr0;
    json::json_pointer ptr1("");
    json::json_pointer ptr2("/foo");

    // compare JSON pointers
    std::cout << std::boolalpha
              << "\"" << ptr0 << "\" != \"" << ptr0 << "\": " << (ptr0 != ptr0) << '\n'
              << "\"" << ptr0 << "\" != \"" << ptr1 << "\": " << (ptr0 != ptr1) << '\n'
              << "\"" << ptr1 << "\" != \"" << ptr2 << "\": " << (ptr1 != ptr2) << '\n'
              << "\"" << ptr2 << "\" != \"" << ptr2 << "\": " << (ptr2 != ptr2) << std::endl;
}

Output:

"" != "": false
"" != "": false
"" != "/foo": true
"/foo" != "/foo": false

Example: (2) Comparing JSON pointers and strings

The example demonstrates comparing JSON pointers and strings, and when doing so may raise an exception.

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

using json = nlohmann::json;

int main()
{
    // different JSON pointers
    json::json_pointer ptr0;
    json::json_pointer ptr1("");
    json::json_pointer ptr2("/foo");

    // different strings
    std::string str0("");
    std::string str1("/foo");
    std::string str2("bar");

    // compare JSON pointers and strings
    std::cout << std::boolalpha
              << "\"" << ptr0 << "\" != \"" << str0 << "\": " << (ptr0 != str0) << '\n'
              << "\"" << str0 << "\" != \"" << ptr1 << "\": " << (str0 != ptr1) << '\n'
              << "\"" << ptr2 << "\" != \"" << str1 << "\": " << (ptr2 != str1) << std::endl;

    try
    {
        std::cout << "\"" << str2 << "\" != \"" << ptr2 << "\": " << (str2 != ptr2) << std::endl;
    }
    catch (const json::parse_error& ex)
    {
        std::cout << ex.what() << std::endl;
    }
}

Output:

"" != "": false
"" != "": false
"/foo" != "/foo": false
"bar" != "/foo": [json.exception.parse_error.107] parse error at byte 1: JSON pointer must be empty or begin with '/' - was: 'bar'

Version history

1. Added in version 2.1.0.
2. Added for backward compatibility and deprecated in version 3.11.2.