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constexpr subtype_type subtype() const noexcept;

Returns the numerical subtype of the value if it has a subtype. If it does not have a subtype, this function will return subtype_type(-1) as a sentinel value.

Return value

the numerical subtype of the binary value, or subtype_type(-1) if no subtype is set

Exception safety

No-throw guarantee: this function never throws exceptions.





The example below demonstrates how the subtype can be retrieved with subtype. Note how subtype_type(-1) is returned for container c1.

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

// define a byte container based on std::vector
using byte_container_with_subtype = nlohmann::byte_container_with_subtype<std::vector<std::uint8_t>>;

int main()
    std::vector<std::uint8_t> bytes = {{0xca, 0xfe, 0xba, 0xbe}};

    // create container
    auto c1 = byte_container_with_subtype(bytes);

    // create container with subtype
    auto c2 = byte_container_with_subtype(bytes, 42);

    std::cout << "c1.subtype() = " << c1.subtype()
              << "\nc2.subtype() = " << c2.subtype() << std::endl;

    // in case no subtype is set, return special value
    assert(c1.subtype() == static_cast<byte_container_with_subtype::subtype_type>(-1));


c1.subtype() = 18446744073709551615
c2.subtype() = 42

Version history

  • Added in version 3.8.0
  • Fixed return value to properly return subtype_type(-1) as documented in version 3.10.0.

Last update: September 18, 2022