使用boost ptree将std :: list序列化为json [英] Serializing std::list into json with boost ptree

问题描述

好吧，所以我在最近几天碰到我的头，但我仍然无法得到它的权利。我有一个std :: list容器，我想将其序列化为JSON字符串，使我可以通过网络发送它。

注意：使用以下代码编译代码：

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

我帮助了这和这是

以下是我的 DBAccess1.h 文件。

  #ifndef DBAccess1_HH 
＃ define DBAccess1_HH 
 
 #include< list> //我为了可读性删除了一些头
 #include< boost / serialization / list.hpp> 
 #include< boost / property_tree / ptree.hpp> 
 #include< boost / property_tree / json_parser.hpp> 
 
 using namespace std; 
使用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&运算符<< （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 DBAccess11.cpp 文件，其中定义了所有函数

  #include< list& //我为了可读性删除了一些头
 #include< boost / property_tree / ptree.hpp> 
 #include< boost / property_tree / json_parser.hpp> 
 #include< boost / serialization / list.hpp> 
 #includeDBAccess1.h
 
使用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信息; 
 info.siteID = A; 
 info.siteCode = B; 
 
 cout<<准备将数据推入列表<< endl; 
 Site_Code_list.push_back（info）; 
 cout<<已成功推送数据<< 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<< List的大小是：< s<< endl; 
 for（list< SiteCode> :: iterator it = Site_Code_list.begin（）; it！= Site_Code_list.end（）; it ++）
 cout< * it< ; 
} 
  

以下是 main.cpp

  #include< list> //我为了可读性删除了一些头
 #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<< \\\
\\\
All语句已正确执行\\\
\\\
; 
 return 0; 
} 
  

我得到的错误如下：

  DBAccess11.cpp：在成员函数'std :: list< SiteCode> sqliteDB :: GET_ALL_Site_Code（）'：
 DBAccess11.cpp：80：38：错误：Site_Code_list之前的主表达式
（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）
 ^ 
  

/ p>

（1）这是否是使用boost将 std :: list转换成JSON 的正确方法？如果否，那么应该如何做呢？
（注意 - 我只能使用boost而没有其他库）

（2）如果我的方法是正确的，

解决方案

树中的路径总是字符串。编译器会在消息的其余部分告诉你这一点。可以证明文档是一个更易读的来源：

两个 key_type 和 data_type 是可配置的，但通常为 std :: string 此处

b
$ b

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

因此修复的本质是

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

我有一些侧面跟踪清理代码，所以这里：

自包含示例

  header 
 #include< ostream> 
 
 struct SiteCode {
 int id; 
 int code; 
 
 SiteCode（int id，int code）：id（id），code（code）
 {} 
 
 friend inline std :: ostream& <（std :: ostream& out，SiteCode const& site）{
 return out< （<< site.id<<，<< site.code<<）; 
} 
}; 
 
 #include< list> //我为了可读性删除了一些头
 
 // FILE：sqliteDB头
类sqliteDB {
使用Records = std :: list< SiteCode> ;; 
记录_records; 
 
 public：
 void load（）; 
记录const& get（）const {return _records; } 
 void printList（）const; 
 void writeJson（std :: ostream& os）const; 
}; 
 
 // FILE：一些sqlpp.hpp实用程序头（仅限内联实现）
 #include< memory> 
 #include< sqlite3.h> 
 
命名空间sqlpp {
使用database = std :: shared_ptr< :: sqlite3> ;; 
 
 void perror（int rc）{
 if（rc！= SQLITE_OK）throw std :: runtime_error（:: sqlite3_errstr（rc））; 
} 
 
 struct语句{
静态语句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; // keep it around for the lifetime of _stmt 
 handle _stmt; 
 
语句（handle& h，database& db）：_db（db），_stmt（std :: move（h））{} 
}; 
 
数据库打开（char const * path）{
 :: sqlite3 * db = nullptr; 
 perror（:: sqlite3_open（path，& db））; 
 
返回数据库（db，:: sqlite3_close）; 
} 
 
语句prepare（database db，std :: string const& sql）{
 return statement :: prepare（db，sql）; 
} 
} 
 
 // FILE：sqliteDB实现文件
 #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程序
 template< typename List> 
 static void printList（List const& list）{
 int s = list.size（）; 
 std :: cout<< 记录数是：< s<< \\\
; 
 
 for（auto& r：list）std :: cout<< r<< ; 
} 
 
 void dump（sqliteDB const& db）{
 printList（db.get（））; 
 std :: cout<< \\\
 ============== [AS JSON] =============== \\\
; 
 db.writeJson（std :: cout）; 
} 
 
 int main（）{
 sqliteDB db; 
 
 std :: cout<< before loading：\\\
; 
 dump（db）; 
 
 std :: cout<< 加载后：\\\
; 
 db.load（）; 
 dump（db）; 
} 
  

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

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

输出

 在装载之前：
记录数为：0 
 
 ====== ======== [AS JSON] =============== 
 {} 
装载后：
记录数为： 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 8798，8：20601，9：21213，10：18222} 
  

okay, so I am banging my head on this for last couple of days but still I am unable to get it right. I have a std::list container and I want to serialize it into JSON string so that I can send it over network.

NOTE: I compile my code using following:

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

I took help of this and this

Below is my DBAccess1.h file.

#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**

Below is the DBAccess11.cpp file where all the functions are defined

#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 << " ";
}

Below is 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;
}

The error I get is as follows:

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)
                                                ^

My Questions:

(1)Is this the right way to convert std::list into JSON using boost ? if NO then how should it be done ? (Note- I can only use boost and no other library )

(2) If my approach is right then what changes shall I make to correct it ?

解决方案

Paths in your tree are always strings. The compiler will tell you this in the remainder of the message. Arguably the documentation is a more readable source:

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);

So the essence of the fix is

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

I got a little bit side-tracked cleaning up the code, so here goes:

Self Contained Sample

// 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);
}

Just compile as g++ -std=c++11 -g -Wall -Wextra -pedantic main.cpp -lsqlite3 and get:

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

Output

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"}

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