json/api/json_pointer/operator_eq.md

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)

// since C++20
class json_pointer {
    template<typename RefStringTypeRhs>
    bool operator==(
        const json_pointer<RefStringTypeRhs>& rhs) const noexcept;  // (1)

    bool operator==(const string_t& rhs) const;                     // (2)
};

1. Compares two JSON pointers for equality by comparing their reference tokens.

2. Compares a JSON pointer and a string or a string and a JSON pointer for equality 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 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:
   • Throws parse_error.107 if the given JSON pointer s is nonempty and does not begin with a slash (/); see example below.
   • 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

!!! warning "Deprecation"

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

See the [migration guide](../../integration/migration_guide.md#json-pointers) for how to update existing code.

Examples

??? example "Example: (1) Comparing JSON pointers"

The example demonstrates comparing JSON pointers.
    
```cpp
#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:

```
"" == "": true
"" == "": true
"" == "/foo": false
"/foo" == "/foo": true

```

??? example "Example: (2) Comparing JSON pointers and strings"

The example demonstrates comparing JSON pointers and strings, and when doing so may raise an exception.
    
```cpp
#include <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:

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

```

See also

• operator!= compare for inequality
• operator<=> comparison: 3-way (C++20)

Version history

1. Added in version 2.1.0. Added C++20 member functions in version 3.11.2.
2. Added for backward compatibility and deprecated in version 3.11.2.