怎样用C++写一个json解析类

以下是一个简单的C++ JSON解析类的示例代码：

#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <map>

using namespace std;

class JsonParser {
private:
    string json;
    int index;

public:
    JsonParser(string json) {
        this->json = json;
        this->index = 0;
    }

    bool isWhiteSpace(char c) {
        return c == ' ' || c == '\t' || c == '\n' || c == '\r';
    }

    void skipWhiteSpace() {
        while (index < json.length() && isWhiteSpace(json[index])) {
            index++;
        }
    }

    string parseString() {
        string result = "";
        index++; // skip opening quote
        while (index < json.length()) {
            char c = json[index++];
            if (c == '"') {
                return result;
            } else if (c == '\\') {
                char next = json[index++];
                if (next == 'n') {
                    result += '\n';
                } else if (next == 't') {
                    result += '\t';
                } else {
                    result += next;
                }
            } else {
                result += c;
            }
        }
        return result;
    }

    double parseNumber() {
        string numStr = "";
        bool isNegative = false;
        if (json[index] == '-') {
            isNegative = true;
            index++;
        }
        while (index < json.length() && isdigit(json[index])) {
            numStr += json[index++];
        }
        if (index < json.length() && json[index] == '.') {
            numStr += '.';
            index++;
            while (index < json.length() && isdigit(json[index])) {
                numStr += json[index++];
            }
        }
        return isNegative ? -1 * stod(numStr) : stod(numStr);
    }

    bool parseBoolean() {
        if (json[index] == 't') {
            index += 4; // true
            return true;
        } else {
            index += 5; // false
            return false;
        }
    }

    void skipNull() {
        index += 4; // null
    }

    vector<JsonParser> parseArray() {
        vector<JsonParser> result;
        index++; // skip opening bracket
        skipWhiteSpace();
        while (index < json.length() && json[index] != ']') {
            result.push_back(parseValue());
            skipWhiteSpace();
            if (index < json.length() && json[index] == ',') {
                index++;
                skipWhiteSpace();
            }
        }
        index++; // skip closing bracket
        return result;
    }

    map<string, JsonParser> parseObject() {
        map<string, JsonParser> result;
        index++; // skip opening brace
        skipWhiteSpace();
        while (index < json.length() && json[index] != '}') {
            string key = parseString();
            skipWhiteSpace();
            index++; // skip colon
            skipWhiteSpace();
            result[key] = parseValue();
            skipWhiteSpace();
            if (index < json.length() && json[index] == ',') {
                index++;
                skipWhiteSpace();
            }
        }
        index++; // skip closing brace
        return result;
    }

    JsonParser parseValue() {
        skipWhiteSpace();
        char c = json[index];
        if (c == '{') {
            return parseObject();
        } else if (c == '[') {
            return parseArray();
        } else if (c == '"') {
            return parseString();
        } else if (isdigit(c) || c == '-') {
            return parseNumber();
        } else if (c == 't' || c == 'f') {
            return parseBoolean();
        } else if (c == 'n') {
            skipNull();
            return NULL;
        } else {
            throw "Invalid JSON";
        }
    }
};

int main() {
    string jsonStr = R"(
        {
            "name": "John Smith",
            "age": 42,
            "isMarried": true,
            "address": {
                "street": "123 Main St",
                "city": "New York",
                "state": "NY"
            },
            "phoneNumbers": [
                "555-1234",
                "555-5678"
            ]
        }
    )";
    JsonParser parser(jsonStr);
    map<string, JsonParser> obj = parser.parseObject();
    cout << "Name: " << obj["name"].parseString() << endl;
    cout << "Age: " << obj["age"].parseNumber() << endl;
    cout << "Is Married: " << obj["isMarried"].parseBoolean() << endl;
    map<string, JsonParser> address = obj["address"].parseObject();
    cout << "Street: " << address["street"].parseString() << endl;
    cout << "City: " << address["city"].parseString() << endl;
    cout << "State: " << address["state"].parseString() << endl;
    vector<JsonParser> phoneNumbers = obj["phoneNumbers"].parseArray();
    cout << "Phone Numbers: ";
    for (JsonParser phoneNumber : phoneNumbers) {
        cout << phoneNumber.parseString() << " ";
    }
    cout << endl;
    return 0;
}
``