【C++ RapidJson】使用RapidJson写入文件

使用RapidJson写入文件（C++）

本文部分内容由AI生成

最初，我希望能够使用RapidJson 向文件中写入一个三级json。其二级json是由for循环计算生成的。但是写来写去，发现有很多乱码，好像是字符串空间在写入流之前就销毁的原因？（不确定）于是，使用AI生成了以下例子。

基于C++ 对json文件进行写入

#include <rapidjson/document.h>
#include <rapidjson/writer.h>
#include <rapidjson/stringbuffer.h>
#include <rapidjson/prettywriter.h> // for prettywriter
#include <rapidjson/filereadstream.h>
#include <rapidjson/filewritestream.h>
#include <cstdio>

using namespace rapidjson;

int main() {
    // 创建一个JSON对象
    Document d;
    d.SetObject();

    Document::AllocatorType& allocator = d.GetAllocator();
    d.AddMember("name", Value().SetString("John Doe", allocator), allocator);
    d.AddMember("age", 30, allocator);
    d.AddMember("is_student", false, allocator);

    // 写入文件
    FILE* fp = fopen("example.json", "wb"); // 非Windows平台可能需要使用 "w"
    char writeBuffer[65536];
    FileWriteStream os(fp, writeBuffer, sizeof(writeBuffer));

    PrettyWriter<FileWriteStream> writer(os);   // 注意，可以不使用PrettyWriter，不过，写出来的结构不好看，Pretty会将json写成树结构
    d.Accept(writer);

    fclose(fp);

    // 读取文件
    fp = fopen("example.json", "rb"); // 非Windows平台可能需要使用 "r"
    char readBuffer[65536];
    FileReadStream is(fp, readBuffer, sizeof(readBuffer));

    Document d2;
    d2.ParseStream(is);
    fclose(fp);

    // 输出读取的内容（简单示例）
    printf("Name: %s\n", d2["name"].GetString());
    printf("Age: %d\n", d2["age"].GetInt());
    printf("Is Student: %s\n", d2["is_student"].GetBool() ? "true" : "false");

    return 0;
}

使用RapidJson对文件进行写入，写入的是一个二级json(包含多个对象)

#include <cstdio>
#include <rapidjson/document.h>
#include <rapidjson/writer.h>
#include <rapidjson/stringbuffer.h>
#include <rapidjson/prettywriter.h> // for PrettyWriter
#include <rapidjson/filewritestream.h>

using namespace rapidjson;

int main() {
    // 创建一个JSON文档，这将作为我们的根对象
    Document document;
    document.SetObject();
    Document::AllocatorType& allocator = document.GetAllocator();

    // 创建一个JSON数组
    Value array(kArrayType);

    // 创建第一个对象并添加到数组
    Value object1(kObjectType);
    object1.AddMember("id", 1, allocator);
    object1.AddMember("name", "John Doe", allocator);
    array.PushBack(object1, allocator);

    // 创建第二个对象并添加到数组
    Value object2(kObjectType);
    object2.AddMember("id", 2, allocator);
    object2.AddMember("name", "Jane Smith", allocator);
    array.PushBack(object2, allocator);

    // 创建第三个对象并添加到数组
    Value object3(kObjectType);
    object3.AddMember("id", 3, allocator);
    object3.AddMember("name", "Alice Johnson", allocator);
    array.PushBack(object3, allocator);

    // 将数组添加到根对象
    document.AddMember("users", array, allocator);

    // 将JSON写入文件
    FILE* fp = fopen("output.json", "wb"); // 非Windows平台可能需要使用 "w"
    char writeBuffer[65536];
    FileWriteStream os(fp, writeBuffer, sizeof(writeBuffer));

    PrettyWriter<FileWriteStream> writer(os);
    document.Accept(writer);

    fclose(fp);

    return 0;
}

使用RapidJson写一个包含多个对象的二级json文件，使用for循环

#include <cstdio>
#include <rapidjson/document.h>
#include <rapidjson/writer.h>
#include <rapidjson/stringbuffer.h>
#include <rapidjson/prettywriter.h> // for PrettyWriter
#include <rapidjson/filewritestream.h>

using namespace rapidjson;

int main() {
    // 创建一个JSON文档，作为根对象
    Document document;
    document.SetObject();
    Document::AllocatorType& allocator = document.GetAllocator();

    // 创建一个JSON数组
    Value usersArray(kArrayType);

    // 使用for循环生成多个用户对象
    for (int i = 1; i <= 5; ++i) {
        Value userObject(kObjectType);
        // 为了示例简单，这里使用i作为id和name的一部分
        userObject.AddMember("id", i, allocator);

        // 创建一个具有动态字符串的Value
        std::string name = "User " + std::to_string(i);
        Value nameValue;
        nameValue.SetString(name.c_str(), static_cast<SizeType>(name.length()), allocator);
        userObject.AddMember("name", nameValue, allocator);

        // 将用户对象添加到数组中
        usersArray.PushBack(userObject, allocator);
    }

    // 将数组添加到根对象中
    document.AddMember("users", usersArray, allocator);

    // 写入文件
    FILE* fp = fopen("users_output.json", "wb"); // 非Windows平台可能需要使用 "w"
    char writeBuffer[65536];
    FileWriteStream os(fp, writeBuffer, sizeof(writeBuffer));

    PrettyWriter<FileWriteStream> writer(os);
    document.Accept(writer);

    fclose(fp);

    return 0;
}

这段代码首先创建了一个根JSON文档document和一个数组usersArray。通过for循环，我们创建了五个用户对象，每个对象包含id和name字段，其中name是通过将循环的索引i转换为字符串并与"User "连接得到的。这些用户对象被添加到usersArray中，最后这个数组被添加到根文档中，并通过PrettyWriter写入到名为users_output.json的文件中。

结果：

{
    "users": [
        {
            "id": 1,
            "name": "User 1"
        },
        {
            "id": 2,
            "name": "User 2"
        },
        {
            "id": 3,
            "name": "User 3"
        },
        {
            "id": 4,
            "name": "User 4"
        },
        {
            "id": 5,
            "name": "User 5"
        }
    ]
}

使用RapidJson向文件中写入一个三级json

#include <cstdio>
#include <string>
#include <rapidjson/document.h>
#include <rapidjson/prettywriter.h>
#include <rapidjson/filewritestream.h>

using namespace rapidjson;

int main() {
    // 创建根文档
    Document document;
    document.SetObject();
    Document::AllocatorType& allocator = document.GetAllocator();

    // 创建一个JSON数组用于存放部门信息
    Value departmentsArray(kArrayType);

    // 使用for循环添加部门和员工
    for (int depId = 1; depId <= 3; ++depId) {
        Value departmentObject(kObjectType);

        // 部门ID和名称
        departmentObject.AddMember("departmentId", depId, allocator);
        std::string depName = "Department " + std::to_string(depId);
        Value depNameValue;
        depNameValue.SetString(depName.c_str(), allocator);
        departmentObject.AddMember("name", depNameValue, allocator);

        // 为每个部门创建员工数组
        Value employeesArray(kArrayType);
        for (int empId = 1; empId <= 4; ++empId) {
            Value employeeObject(kObjectType);
            employeeObject.AddMember("employeeId", empId, allocator);

            std::string empName = "Employee " + std::to_string(empId) + " of Dep " + std::to_string(depId);
            Value empNameValue;
            empNameValue.SetString(empName.c_str(), allocator);
            employeeObject.AddMember("name", empNameValue, allocator);

            // 将员工对象添加到员工数组
            employeesArray.PushBack(employeeObject, allocator);
        }

        // 将员工数组添加到部门对象
        departmentObject.AddMember("employees", employeesArray, allocator);

        // 将部门对象添加到部门数组
        departmentsArray.PushBack(departmentObject, allocator);
    }

    // 将部门数组添加到根文档
    document.AddMember("departments", departmentsArray, allocator);

    // 写入文件
    FILE* fp = fopen("departments_output.json", "wb"); // 非Windows平台可能需要使用 "w"
    char writeBuffer[65536];
    FileWriteStream os(fp, writeBuffer, sizeof(writeBuffer));

    PrettyWriter<FileWriteStream> writer(os);
    document.Accept(writer);

    fclose(fp);

    return 0;
}

• 我们创建了一个根文档document，它包含了一个名为departments的数组。
• 通过外层for循环，我们为每个部门创建了一个包含基本信息（ID和名称）的对象，并为每个部门创建了一个名为employees的数组。
• 内层for循环为每个部门创建了几个员工对象，每个员工对象包含员工的ID和名称。
• 最后，每个部门对象（包括其员工数组）被添加到部门数组中，整个部门数组最终被添加到根文档中，并通过PrettyWriter写入到一个名为departments_output.json的文件中。

结果

{
    "departments": [
        {
            "departmentId": 1,
            "name": "Department 1",
            "employees": [
                {
                    "employeeId": 1,
                    "name": "Employee 1 of Dep 1"
                },
                {
                    "employeeId": 2,
                    "name": "Employee 2 of Dep 1"
                },
                {
                    "employeeId": 3,
                    "name": "Employee 3 of Dep 1"
                },
                {
                    "employeeId": 4,
                    "name": "Employee 4 of Dep 1"
                }
            ]
        },
        {
            "departmentId": 2,
            "name": "Department 2",
            "employees": [
                {
                    "employeeId": 1,
                    "name": "Employee 1 of Dep 2"
                },
                {
                    "employeeId": 2,
                    "name": "Employee 2 of Dep 2"
                },
                {
                    "employeeId": 3,
                    "name": "Employee 3 of Dep 2"
                },
                {
                    "employeeId": 4,
                    "name": "Employee 4 of Dep 2"
                }
            ]
        },
        {
            "departmentId": 3,
            "name": "Department 3",
            "employees": [
                {
                    "employeeId": 1,
                    "name": "Employee 1 of Dep 3"
                },
                {
                    "employeeId": 2,
                    "name": "Employee 2 of Dep 3"
                },
                {
                    "employeeId": 3,
                    "name": "Employee 3 of Dep 3"
                },
                {
                    "employeeId": 4,
                    "name": "Employee 4 of Dep 3"
                }
            ]
        }
    ]
}