CODEWITHSUNDEEP
c++jsonnlohmann-json
Ank i zle
Ank i zle

Reputation: 2357

JSON to an array of structs in nlohmann json lib

I recently asked this question about converting an array of objects into a vector of structs. I want to do the same thing, but rather vectors I want an array. For example

[
  {
    "Name": "Test",
    "Val": "TestVal"
  },
  {
    "Name": "Test2",
    "Val": "TestVal2"
  }
]

And want an array of of these structs:

struct Test {
  string Name;
  string Val;
};

How can this be possible? I am new to c++ so if I am doing anything wrong please say so.

Upvotes: 0

Views: 3032

Answers (1)

parktomatomi
parktomatomi

Reputation: 4089

The easiest thing to do is use, wherever you can, std::array instead of C arrays. std::array is a C++ analogue to plain arrays that adds all the nice stuff from std::vector like size() and iterators. You can also return them from functions, unlike C arrays.

nlohmann also supports it automatically:

auto parsed = json.get<std::array<Test, 2>>();

Not sure about the library's support for plain ol' C arrays. But you can write a helper function with a little template magic:

template <typename T, size_t N>
void from_json(const nlohmann::json& j, T (&t)[N]) {
    if (j.size() != N) {
        throw std::runtime_error("JSON array size is different than expected");
    }
    size_t index = 0;
    for (auto& item : j) {
        from_json(item, t[index++]);
    }
}

usage:

Test my_array[N];
from_json(json, my_array);

Demo: https://godbolt.org/z/-jDTdj

Upvotes: 2

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