使用C++restSDK调用Binance RESTful API的JSON解析问题排查

Hey there, let's break down your JSON parsing issue with the Binance REST API and Microsoft's cpprestsdk. You mentioned the problem is likely in your print_test function, and that makes sense—cpprestsdk's web::json::value requires type-specific handling, and skipping that will lead to broken parsing or exceptions.

Common Pitfall in Your Original Code #

The core issue is that you're not checking the type of the json::value before accessing its data. Binance's API returns different JSON structures (objects, arrays, strings, numbers) depending on the endpoint, and calling methods like as_string() on an object or array will throw a json_exception.

Fixed print_test Function #

Here's a revised version that handles all common JSON types recursively, so it works with any Binance API response:

void print_test(json::value const & value){
    if(!value.is_null()){
        // Handle JSON objects (key-value pairs)
        if (value.is_object()) {
            auto obj = value.as_object();
            for (const auto& key_value_pair : obj) {
                const std::string& key = key_value_pair.first;
                const json::value& val = key_value_pair.second;
                std::cout << "* " << key << ": ";
                print_test(val); // Recurse to handle nested values
                std::cout << "\n";
            }
        }
        // Handle JSON arrays
        else if (value.is_array()) {
            auto arr = value.as_array();
            std::cout << "[ ";
            for (size_t i = 0; i < arr.size(); ++i) {
                if (i > 0) std::cout << ", ";
                print_test(arr[i]);
            }
            std::cout << " ]";
        }
        // Handle primitive types
        else if (value.is_string()) {
            std::cout << "\"" << value.as_string() << "\"";
        }
        else if (value.is_number()) {
            if (value.is_integer()) {
                std::cout << value.as_integer();
            } else {
                std::cout << value.as_double();
            }
        }
        else if (value.is_boolean()) {
            std::cout << (value.as_bool() ? "true" : "false");
        }
    }
}

Debugging Tips to Confirm the Issue #

1. Print Raw API Response
   Before parsing, output the raw string response to verify you're getting valid JSON from Binance:

   try {
       auto response = client.request(methods::GET, "/api/v3/ticker/price?symbol=BTCUSDT").get();
       // Print raw response first
       std::string raw_response = response.extract_string().get();
       std::cout << "Raw Binance Response:\n" << raw_response << "\n\n";
       // Now parse to JSON
       json::value json_data = response.extract_json().get();
       print_test(json_data);
   } catch (const web::json::json_exception& e) {
       std::cerr << "\nJSON Parsing Error: " << e.what() << "\n";
   } catch (const std::exception& e) {
       std::cerr << "\nGeneral Error: " << e.what() << "\n";
   }
   

2. Catch Exceptions
   cpprestsdk throws specific exceptions for JSON type mismatches. Catching web::json::json_exception will tell you exactly where the parsing failed (e.g., trying to convert an array to a string).
3. Match Binance's API Structure
   Refer to Binance's REST API docs to know what structure to expect:
   • Endpoints like /api/v3/ticker/price return a single object
   • Endpoints like /api/v3/klines return an array of arrays
     Knowing this helps you write targeted parsing code instead of relying solely on a generic print function.

内容的提问来源于stack exchange，提问作者runesbane