c++ return type of function returning json array via nlohmann json.hpp

Question

I am parsing a json file using nlohmann's json.hpp. The part of the json file I am concerned with looks like this:

"image_captureOptions": {
    "captureInterval" : 1000,
    "captureLimit" : 5,
    "imageExtension" : "jpg",
    "imageResizeDims" : [640, 480]
},
...

The relevant parts of the class that parses the json look like this:

namespace json = nlohmann;

class ConfigReader {

    json::json data;

    void readConfigFile(std::string path) {
        std::ifstream inputStream(path);

        inputStream >> data;
}

public:
    ConfigReader() {

    static const std::string defaultPath = "config.json";

    readConfigFile(defaultPath);
}

    int getImageCaptureInterval() { return data["image_captureOptions"]["captureInterval"]; }
    int getImageCaptureLimit() { return data["image_captureOptions"]["captureLimit"]; }
    std::string getImageExtension() { return data["image_captureOptions"]["imageExtension"]; }
    ???? getImageResizeDims() { return data["image_captureOptions"]["imageResizeDims"]; }
};

The question marks on the last line represent my confusion on how to specify the return type of that function.

Answer 1

One of the nice things about this library is that conversions to standard types are built-in and do the things you want them to do (the library also provides for a mechanism to do conversions to and from user-provided types).

In this case, you can just use that:

std::vector<int> getImageResizeDims() {
    return data["image_captureOptions"]["imageResizeDims"];
}

If the json subobject at runtime can't be converted to a std::vector<int>, that conversion will throw a type_error.