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Useful C++ libraries #01 nlohmann:json

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A very nice library for working with Json. It gives us support for this format in several ways, but I would like to present one that I use. Unfortunately, this way works only for our types, which we can edit. As a result, I have doubts about maintaining the Single Responsibility Principle. But don’t forget that this library also has solutions for (de-)serialization of third party types that we cannot modify.

Why I like this library.

  • It is available as a single-file header, which makes it easy to include in a project.

  • Very comprehensive and decent documentation that makes it easy to learn about the available functionality and how to use it yourself.

Example of using Nlohmann::json
struct MyDataType {
    std::string someStrValue;
    double someDoubleValue;
    int someIntValue;

    // Adding (de-) serialization (1)
    NLOHMANN_DEFINE_TYPE_INTRUSIVE(MyDataType, someStrValue, someDoubleValue, someIntValue)

/// Function representing how to turn JSON into our own type
MyDataType toMyDataType(const std::string& rawJson) {
    auto j = nlohmann::json::parse(rawJson); (2)
    auto myDataType = j.get<MyDataType>();
    return myDataType;

/// Function representing how to turn our own type into JSON.
std::string toString(const MyDataType& data) {
    nlohman::json jsonData = data; // This is where the automatic conversion takes place (3)
    return jsonData.dump();
1 First, we need to add a macro that includes serializing and deserializing functions.
2 Then we can already perform JSON deserialization (as a string) to an object,
3 and serialization from the object to JSON.
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