使用 boost ptree 将 std::list 序列化为 json

Question

好的，所以我在过去的几天里一直在努力解决这个问题，但我仍然无法把它做好。我有一个 std::list 容器，我想将它序列化为 JSON 字符串，以便我可以通过网络发送它。

注意： 我使用以下代码编译我的代码：

g++ -std=c++11 -o main main.cpp DBAccess11.cpp -lsqlite3 -lboost_serialization

我得到了this and this

的帮助

下面是我的DBAccess1.h文件。

#ifndef DBAccess1_HH  
#define DBAccess1_HH

#include <list> // I have deleted some header for sake of readability
#include <boost/serialization/list.hpp>
#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/json_parser.hpp>

using namespace std;
using boost::property_tree::ptree;
using boost::property_tree::read_json;
using boost::property_tree::write_json;
using boost::property_tree::basic_ptree;

//================================//   
struct SiteCode
{
      int siteID;
      int siteCode;
};

inline ostream& operator<< (ostream &out, SiteCode &site)
{
    out << "(" << site.siteID << "," << site.siteCode << ")";
    return out;
}
//================================//

class sqliteDB {
    list<SiteCode> Site_Code_list;
public:
    list<SiteCode> GET_ALL_Site_Code();
    void printList();
};
#endif**

下面是定义了所有函数的DBAccess11.cpp文件

#include <list> // I have deleted some header for sake of readability
#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/json_parser.hpp>
#include <boost/serialization/list.hpp>
#include "DBAccess1.h"

using boost::property_tree::ptree;
using boost::property_tree::read_json;
using boost::property_tree::write_json;
using boost::property_tree::basic_ptree;

list<SiteCode> sqliteDB::GET_ALL_Site_Code()
{
        sqlite3 *db;
        const char *sql;
        sqlite3_stmt * stmt;

        int rc = sqlite3_open("/path/to/database.db", &db);
        sql = "SELECT * FROM SiteCode;";       
        rc = sqlite3_prepare_v2(db, sql, -1, &stmt, 0);

    while(sqlite3_step(stmt)==SQLITE_ROW) {

            int A  = sqlite3_column_int(stmt, 0);
            int B = sqlite3_column_int(stmt, 1);

            SiteCode info;
            info.siteID = A;
            info.siteCode = B;              

            cout<<"Preparing to push data into List"<<endl;
            Site_Code_list.push_back(info);
            cout<<"Data was pushed successfully"<<endl;

            ptree pt;
            for (auto& entry: list<SiteCode> Site_Code_list)  //<< ERROR LINE80
            pt.put(entry.siteID, entry.siteCode);
            std::ostringstream buf; 
            write_json (buf, pt, false); 
            cout<< buf.str() << endl;
    }

    sqlite3_finalize(stmt);
    sqlite3_close(db);
    return Site_Code_list;
}
//====================================================//
void sqliteDB::printList()
{
     int s = Site_Code_list.size();
     cout << "The size of List is :" << s << endl;
     for( list<SiteCode> :: iterator it = Site_Code_list.begin(); it !=  Site_Code_list.end(); it++)     
     cout << *it << " ";
}

下面是main.cpp

#include <list> // I have deleted some header for sake of readability
#include <boost/serialization/list.hpp>
#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/json_parser.hpp>

using namespace std;
using boost::property_tree::ptree;
using boost::property_tree::read_json;
using boost::property_tree::write_json;
using boost::property_tree::basic_ptree;

int main()
{
    sqliteDB object1;
    object1.GET_ALL_Site_Code();
    object1.printList();
    cout << "\n\nAll the statement were executed properly\n\n";
    return 0;
}

我得到的错误如下：

DBAccess11.cpp: In member function ‘std::list<SiteCode> sqliteDB::GET_ALL_Site_Code()’:
DBAccess11.cpp:80:38: error: expected primary-expression before ‘Site_Code_list’
 for (auto& entry: list<SiteCode> Site_Code_list)
                                  ^
DBAccess11.cpp:80:38: error: expected ‘)’ before ‘Site_Code_list’
DBAccess11.cpp:80:52: error: expected ‘;’ before ‘)’ token
 for (auto& entry: list<SiteCode> Site_Code_list)
                                                ^

我的问题：

(1)这是使用 boost 将 std::list 转换为 JSON 的正确方法吗？如果没有那么应该怎么做？（注意-我只能使用 boost 而不能使用其他库）

(2) 如果我的方法是正确的，那么我应该做哪些改变来纠正它？

Answer 1

树中的路径始终是字符串。编译器会在消息的其余部分告诉您这一点。可以说文档是一个更具可读性的来源：

Both key_type and data_type are configurable, but will usually be std::string here

The self_type & put(const path_type & path, const Type & value, Translator tr);

所以修复的本质是

pt.put(std::to_string(entry.id), entry.code);

我在清理代码时有点跑题了，所以这里是：

独立示例

// FILE: some header
#include <ostream>

struct SiteCode {
    int id;
    int code;

    SiteCode(int id, int code) : id(id), code(code)
    { }

    friend inline std::ostream &operator<<(std::ostream &out, SiteCode const& site) {
        return out << "(" << site.id << "," << site.code << ")";
    }
};

#include <list> // I have deleted some header for sake of readability

// FILE: sqliteDB header
class sqliteDB {
    using Records = std::list<SiteCode>;
    Records _records;

  public:
    void load();
    Records const& get() const { return _records; }
    void printList() const;
    void writeJson(std::ostream& os) const;
};

// FILE: some sqlpp.hpp utility header (inline implementations only)
#include <memory>
#include <sqlite3.h>

namespace sqlpp {
    using database  = std::shared_ptr<::sqlite3>;

    void perror(int rc) {
        if (rc != SQLITE_OK) throw std::runtime_error(::sqlite3_errstr(rc));
    }

    struct statement {
        static statement prepare(database db, std::string const& sql) {
            ::sqlite3_stmt* stmt = nullptr;
            perror(::sqlite3_prepare_v2(db.get(), sql.c_str(), -1, &stmt, 0));

            return { handle(stmt, ::sqlite3_finalize), db };
        }

        int step()            { return ::sqlite3_step(_stmt.get()); }
        int column_int(int c) { return ::sqlite3_column_int(_stmt.get(), c); }
      private:
        using handle = std::shared_ptr<::sqlite3_stmt>;
        database _db; // keeping it around for the lifetime of _stmt
        handle _stmt;

        statement(handle&& h, database& db) : _db(db), _stmt(std::move(h)) { }
    };

    database open(char const* path) {
        ::sqlite3* db = nullptr;
        perror(::sqlite3_open(path, &db));

        return database(db, ::sqlite3_close);
    }

    statement prepare(database db, std::string const& sql) {
        return statement::prepare(db, sql);
    }
}

// FILE: sqliteDB implementation file
#include <boost/property_tree/json_parser.hpp>
#include <boost/property_tree/ptree.hpp>

void sqliteDB::load() {
    using namespace sqlpp;

    auto stmt = prepare(open("/tmp/database.db"), "SELECT ID, CODE FROM SiteCode;");

    while (stmt.step() == SQLITE_ROW)         
        _records.emplace_back(stmt.column_int(0), stmt.column_int(1));
}

void sqliteDB::writeJson(std::ostream& os) const {
    using namespace boost::property_tree;
    ptree pt;

    for (auto &entry : _records)
        pt.put(std::to_string(entry.id), entry.code);

    write_json(os, pt, false);
}

// FILE: main program
template <typename List>
static void printList(List const& list) {
    int s = list.size();
    std::cout << "The number of Records is: " << s << "\n";

    for (auto& r : list) std::cout << r << " ";
}

void dump(sqliteDB const& db) {
    printList(db.get());
    std::cout << "\n==============[ AS JSON ]===============\n";
    db.writeJson(std::cout);
}

int main() { 
    sqliteDB db;

    std::cout << "before loading: \n";
    dump(db);

    std::cout << "after loading: \n";
    db.load();
    dump(db);
}

只需编译为g++ -std=c++11 -g -Wall -Wextra -pedantic main.cpp -lsqlite3并得到：

sehe@desktop:/tmp$ sqlite3 database.db <<< "create table SiteCode (id int primary key, code int);"
sehe@desktop:/tmp$ for a in {1..10}; do echo "insert into SiteCode(ID,CODE) VALUES($a, $RANDOM);"; done | sqlite3 database.db 
sehe@desktop:/tmp$ ./test

输出

before loading: 
The number of Records is: 0

==============[ AS JSON ]===============
{}
after loading: 
The number of Records is: 10
(1,5591) (2,31578) (3,30641) (4,4850) (5,1628) (6,5133) (7,8798) (8,20601) (9,21213) (10,18222) 
==============[ AS JSON ]===============
{"1":"5591","2":"31578","3":"30641","4":"4850","5":"1628","6":"5133","7":"8798","8":"20601","9":"21213","10":"18222"}

Answer 2

好的，所以正在研究 sehe 上面提供的解决方案。我终于能够得到正确的输出。我不得不根据我的需要修改他的解决方案。这里的答案如下。感谢 sehe。

下面是我的DBAccess1.h文件：

#ifndef DBAccess1_HH
#define DBAccess1_HH

#include <sqlite3.h>
#include <list>   
#include <boost/serialization/list.hpp>
#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/json_parser.hpp>

using namespace std;
using boost::property_tree::ptree;
using boost::property_tree::read_json;
using boost::property_tree::write_json;
using boost::property_tree::basic_ptree;

//=========================//
struct SiteCode
{
  int siteID;
  int siteCode;

    friend inline std::ostream &operator<<(std::ostream &out, SiteCode const& site) {
    return out << "(" << site.siteID << "," << site.siteCode << ")";
    }
};
//=========================//
class sqliteDB {

using Records = std::list<SiteCode>;
Records Site_Code_list;

public:

list<SiteCode> GET_ALL_Site_Code();
Records const& get() const { return Site_Code_list; }
void writeJson(std::ostream& os) const;
void printList() const;
};

#endif

下面是DBAccess11.cpp

#include <ostream>
#include <boost/serialization/list.hpp>
#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/json_parser.hpp>

#include "DBAccess1.h"

using boost::property_tree::ptree;
using boost::property_tree::read_json;
using boost::property_tree::write_json;
using boost::property_tree::basic_ptree;

list<SiteCode> sqliteDB::GET_ALL_Site_Code()
{
        sqlite3 *db;
        const char *sql;
        sqlite3_stmt * stmt;

        int rc = sqlite3_open("/path.to/database.db", &db);

        sql = "SELECT * FROM SiteCode;";

        rc = sqlite3_prepare_v2(db, sql, -1, &stmt, 0);

        while(sqlite3_step(stmt)==SQLITE_ROW) {

            int A  = sqlite3_column_int(stmt, 0);
            int B = sqlite3_column_int(stmt, 1);

            SiteCode info;
            info.siteID = A;
            info.siteCode = B;              

            cout<<"Preparing to push data into List"<<endl;
            Site_Code_list.push_back(info);
            cout<<"Data was pushed successfully"<<endl;
    }
    sqlite3_finalize(stmt);
    sqlite3_close(db);
    return Site_Code_list;
}
//==============================================================//
void sqliteDB::writeJson(std::ostream& os) const
{
    using namespace boost::property_tree;
    ptree pt;

    for (auto &entry : Site_Code_list)
        pt.put(std::to_string(entry.siteID), entry.siteCode);

    write_json(os, pt, false);
}
//=========================================================//

下面是main.cpp

#include <ostream>

#include <boost/serialization/list.hpp>
#include <boost/property_tree/ptree.hpp>
#include <boost/property_tree/json_parser.hpp>

#include "DBAccess1.h"

using namespace std ;
using boost::property_tree::ptree;
using boost::property_tree::read_json;
using boost::property_tree::write_json;
using boost::property_tree::basic_ptree;

template <typename List>
static void printList(List const& list) {
    int s = list.size();
    std::cout << "The number of Records is: " << s << "\n";
    for (auto& r : list) std::cout << r << " ";
}

void dump(sqliteDB const& db) {
    printList(db.get());
    std::cout << "\n==============[ AS JSON ]===============\n";
    db.writeJson(std::cout);
}

int main()
{

    sqliteDB object1;

    std::cout << "before loading: \n";
    dump(object1);

    std::cout << "after loading: \n";
    object1.GET_ALL_Site_Code();
    dump(object1);

    return 0;
}

编译以上使用：

g++ -std=c++11 -o main main.cpp DBAccess11.cpp -lsqlite3 -lboost_serialization

下面是我得到的输出：

before loading: 
The number of Records is: 0

==============[ AS JSON ]===============
{}
after loading: 
Preparing to push data into List
Data was pushed successfully
Preparing to push data into List
Data was pushed successfully
Preparing to push data into List
Data was pushed successfully
Preparing to push data into List
Data was pushed successfully
Preparing to push data into List
Data was pushed successfully
Preparing to push data into List
Data was pushed successfully
Preparing to push data into List
Data was pushed successfully
Preparing to push data into List
Data was pushed successfully
Preparing to push data into List
Data was pushed successfully
Preparing to push data into List
Data was pushed successfully
The number of Records is: 10
(7,786) (8,78) (9,785) (10,998) (11,656) (13,23) (14,7) (15,74) (16,954) (17,752) 
==============[ AS JSON ]===============
{"7":"786","8":"78","9":"785","10":"998","11":"656","13":"23","14":"7","15":"74","16":"954","17":"752"}

使用 boost ptree 将 std::list 序列化为 json

Serializing std::list into json with boost ptree

c++

serialization

json

boost

boost-propertytree