SQL 空返回 "stops" 使用 odbc 的 c++ 返回

我的表看起来有点像这样

Table cards
|  CardId  |  cityName| eventName|  Colour|
|----------+----------+----------+--------|
|     29   |   "test" |   null   | "blue" |
|     2    |   null   |  "test   |  null  |

现在让我们说我做

 "select * from card where CardId = 29"

我的返回向量将包含："测试"，仅此而已。因此，它基本上将包含事件名称之前的所有数据。同样的事情也适用于以下内容

 "select * from card where CardId = 2" 

连接到数据库的C++代码：

void SqlConnection::sqlExecuteSelect(string *select) {
SQLCHAR DBName[20] = "PandemicMain";
SQLCHAR SQLStmt[4000] = { 0 };
SQLRETURN rc = SQL_SUCCESS;
ODBC_Class Example;
if (Example.ConHandle != NULL)
{
    rc = SQLConnect(Example.ConHandle, DBName, SQL_NTS, (SQLCHAR *) "concordia", SQL_NTS, (SQLCHAR *) "University4", SQL_NTS);
    // Allocate An SQL Statement Handle 
    rc = SQLAllocHandle(SQL_HANDLE_STMT, Example.ConHandle, &Example.StmtHandle);
    rc = SQLExecDirect(Example.StmtHandle, SQLStmt, SQL_NTS);
    if (rc == SQL_SUCCESS)
    {
        // Define A SELECT SQL Statement  
        char* finalSelect = new char[select->length() + 1];
        std::strcpy(finalSelect, select->c_str());
        strcpy((char *)SQLStmt, finalSelect);
        // Prepare And Execute The SQL Statement  
            rc = SQLExecDirect(Example.StmtHandle, SQLStmt, SQL_NTS);
        // Display The Results Of The SQL Query  
        if (!rc == SQL_SUCCESS) {
            cout << "*************************** failed ***************" << endl;
        }
        if (rc == SQL_SUCCESS)
        {
            Example.GetResultset();
            Connection.colData = Example.colData;

            // At this point you would want to do something  
            // with the resultset, such as display it.  
        }
    }
    // Free The SQL Statement Handle  
    if (Example.StmtHandle != NULL)
        SQLFreeHandle(SQL_HANDLE_STMT, Example.StmtHandle);
    // Disconnect From The Northwind Sample Database  
    rc = SQLDisconnect(Example.ConHandle);
}
}

Odbc.h

#pragma once
////////////////////////////////////////
#include <windows.h>
#include <sql.h>
#include<sqltypes.h>
#include<sqlext.h>
#include <string>
#include <vector>
#include <iostream>
using namespace std;

// Define The ODBC_Class Class
class ODBC_Class
{
  struct ColDescription
  {
    SQLSMALLINT colNumber;
    SQLCHAR colName[80];
    SQLSMALLINT nameLen;
    SQLSMALLINT dataType;
    SQLULEN colSize;
    SQLSMALLINT decimalDigits;
    SQLSMALLINT nullable;
  };
// Attributes
public:
    SQLHANDLE EnvHandle;
    SQLHANDLE ConHandle;
    SQLHANDLE StmtHandle;
    SQLRETURN rc;
    vector<ColDescription> cols;
    vector< vector<string> > colData;
    // Operations
public:
    ODBC_Class(); // Constructor
    ~ODBC_Class(); // Destructor
    SQLRETURN GetResultset();
    void DescribeColumns();
private:
    _inline SQLRETURN Describe(ColDescription& c);
    SQLRETURN GetColData(int colnum, string& str);
};

奥德布.cpp

 #include "ODBC.h"
//***************************CODE FROM 
http://www.dreamincode.net/forums/topic/127959-odbc-c-example/ 
*************************************/
// Define The ODBC_Class Class

// Define The Class Constructor
ODBC_Class::ODBC_Class()
{
// Initialize The Return Code Variable
rc = SQL_SUCCESS;
// Allocate An Environment Handle
rc = SQLAllocHandle(SQL_HANDLE_ENV, SQL_NULL_HANDLE, &EnvHandle);
// Set The ODBC Application Version To 3.x
if (rc == SQL_SUCCESS)
    rc = SQLSetEnvAttr(EnvHandle, SQL_ATTR_ODBC_VERSION,
    (SQLPOINTER)SQL_OV_ODBC3, SQL_IS_UINTEGER);
// Allocate A Connection Handle
if (rc == SQL_SUCCESS)
    rc = SQLAllocHandle(SQL_HANDLE_DBC, EnvHandle, &ConHandle);
}
// Define The Class Destructor
ODBC_Class::~ODBC_Class()
{
// Free The Connection Handle
if (ConHandle != NULL)
    SQLFreeHandle(SQL_HANDLE_DBC, ConHandle);
// Free The Environment Handle
if (EnvHandle != NULL)
    SQLFreeHandle(SQL_HANDLE_ENV, EnvHandle);
}
// Get the data for one column and return the info in the form
// of a std::string.  The ODBC driver will make all necessary
// data conversions from whatever type the data is in the database
// to SQL_CHAR.  You could make this function more comples by 
// getting the return type as it appears in the database then constructing
// a VARIANT object to hold the data.
SQLRETURN ODBC_Class::GetColData(int colnum, string& str)
{
  SQLCHAR buf[255] = { 0 };
  if ((rc = SQLGetData(StmtHandle, colnum, SQL_CHAR, buf, sizeof(buf), NULL)) == SQL_SUCCESS)
      str = reinterpret_cast<char*>(buf);
 return rc;
}
//
// Define The ShowResults() Member Function
SQLRETURN ODBC_Class::GetResultset()
{
   // Get all column description
   DescribeColumns();
   // erase anything that's in the colData vector
   colData.clear();
   // fetch a row from the resultset
   while (SQLFetch(StmtHandle) == SQL_SUCCESS)
   {
       // vector of strings to hold the column data
       vector<string> col;
       string data;
       // column counter
       int i = 1;
       // get the data for each column and add it to 
       // the col vector
       while (GetColData(i, data) == SQL_SUCCESS)
       {
           col.push_back(data);
           ++i; // increment the column number
       }
       // add column data to the colData vector
       colData.push_back(col);
    }
   return SQL_SUCCESS;
  }
 // Get the description for one column in the resultset.
 // This was made a seprate function to simplify the coding
 SQLRETURN  ODBC_Class::Describe(ColDescription& c)
{
    return SQLDescribeCol(StmtHandle, c.colNumber,
         c.colName, sizeof(c.colName), &c.nameLen,
         &c.dataType, &c.colSize, &c.decimalDigits, &c.nullable);
}
// Get the description for all the columns in the resultset.
void ODBC_Class::DescribeColumns()
{
    ColDescription c;
    c.colNumber = 1;
     cols.clear();
    while (Describe(c) == SQL_SUCCESS)
   {
      cols.push_back(c);
       ++c.colNumber;
   }
 }

使用 SQLGetDiagRec 之后

我收到以下消息：

Sql状态： 22002

所以我确实知道这意味着"需要但未提供的指示符变量">

无论如何要处理这个？