如何使用sqlite3的C++

Question

我試圖整數數據轉換爲字符串整數轉換爲字符串，但我發現了錯誤cannot convert 'int*' to 'const char*' for argument '2' to 'char* strcat(char*, const char*)'

嘿，夥計們，請解決這些問題，在哪裏我dowrong？

#include <iostream> 
    using namespace std; 
    #include "sqlite3.h" 
    #include<string.h> 
    #include <sstream> 
    #define STRING_MAX 32 

    typedef struct metadata_t 
    { 
     char session_username[256]; 
     int user_id[256]; 
     int session_id[256]; 
     char buffer[256]; 
    }metadata_t; 

    void insertdata1(metadata_t *data); 

    int main (int argc, const char * argv[]) 
     { 

     struct metadata_t *data; 
     cin >> *data->user_id; 
     cin >> data->session_username; 
     cin >> *data->session_id; 
     cin >> data->buffer; 


     insertdata1(data); 

     } 

    void insertdata1(metadata_t *data) 
     { 

     // char *buff1,*buff2; 
      sqlite3 *db; 
      sqlite3_open("test1.db", & db); 
      string createQuery = "CREATE TABLE IF NOT EXISTS items (user_id INTEGER PRIMARY KEY, session_username TEXT,Session_id INTEGER,buffer TEXT,));"; 
      sqlite3_stmt *createStmt; 
      cout << "Creating Table Statement" << endl; 
      sqlite3_prepare(db, createQuery.c_str(), createQuery.size(), &createStmt, NULL); 
      cout << "Stepping Table Statement" << endl; 
      if (sqlite3_step(createStmt) != SQLITE_DONE) cout << "Didn't Create Table!" << endl; 


      //itoa(*data->userid,buff1,10); // not work 
      //itoa(*data->userphone,buff2,10);// Integer to String Conversion 

     /* std::string ss; 
      ss << *data->user_id; 
      ss << *data->session_id; 
      std::string user_Id = ss.str(); 
      std::string session_Id = ss.str(); */ // not working 
        char *a="("; 
        char *d=")"; 
        char *b="'"; 
        char *c=","; 
        char str1[1000]; 
        char * str2 = ""; 
        char * g = ";"; 
       strcpy(str1, "INSERT INTO items (user_id,session_username,session_id,buffer)VALUES"); 

       strcat(str1,a); 

       strcat(str1,b); 
       strcat(str1,data->user_id); 
       strcat(str1,b); 
       strcat(str1,c); 
       strcat(str1,b); 
       strcat(str1,data->session_username); 
       strcat(str1,b); 
       strcat(str1,c); 
       strcat(str1,b); 
       strcat(str1,data->session_id); 
       strcat(str1,b); 
       strcat(str1,c); 
       strcat(str1,b); 
       strcat(str1,data->buffer); 
       strcat(str1,b); 
       strcat(str1,d); 
       strcat(str1,g); 

      std::string insertQuery = str1; // WORKS! 
      sqlite3_stmt *insertStmt; 
      cout << "Creating Insert Statement" << endl; 
      sqlite3_prepare(db, insertQuery.c_str(), insertQuery.size(), &insertStmt, NULL); 
      cout << "Stepping Insert Statement" << endl; 
      if (sqlite3_step(insertStmt) != SQLITE_DONE) cout << "Didn't Insert Item!" << endl; 




     }** 

Answer 1

推薦使用std::ostringstream（你需要#include <sstream>）來構造查詢：

std::ostringstream str1; 

str1 << "INSERT INTO items (user_id,session_username,session_id,buffer)VALUES" 
    << a 
    << b // and so on 
    << g; 

const std::string insertQuery = str1.str(); 

下列不分配任何內存，只是聲明瞭一個指針（struct是不是在C需要++ ）：

struct metadata_t *data; 

以及任何解除引用的嘗試都會導致未定義的行爲，很可能是分段錯誤：

cin >> *data->user_id; 

只是聲明它在堆棧上：

metadata_t data; 

，並通過它的地址（或通過引用傳遞）到insertdata1()：

insertdata1(&data); 

不想std::string到char*或char[]：

struct metadata_t 
{ 
    std::string session_username; 
    int user_id[256]; // Did you really mean an array of int here ? 
    int session_id[256]; 
    std::string buffer; 
};