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 |
现在让我说
"select * from card where CardId = 29"
我的返回向量将包含：“test”就是这样。所以它基本上包含所有数据BEFORE eventName。同样的事情将适用于以下
"select * from card where CardId = 2"
连接到db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);
};
Odbc.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后
我收到以下消息：
SqlState：22002
所以我知道这意味着“需要指标变量但不提供”
无论如何处理这个？
答案 0 :(得分：1)
我有一段时间完全相同的错误。基本上，ODBC试图告诉您正在检索的值是NULL。它将使用 SQLGetData（）中的最后一个Param执行此操作，您可以在此处找到更多信息：https://docs.microsoft.com/en-gb/sql/odbc/reference/syntax/sqlgetdata-function
该行：
if ((rc = SQLGetData(StmtHandle, colnum, SQL_CHAR, buf, sizeof(buf), NULL)) == SQL_SUCCESS)
str = reinterpret_cast<char*>(buf);
您需要将传入的NULL值更改为可以填充的值。这是ODBC将尝试填充的缓冲区，如果它是NULL值。它将始终返回您在此字段中返回的列的长度（但如果传递NULL，则不会返回），除非它返回NULL，在这种情况下它需要它。通过ref传递SQLLEN，它应该作为SQL_NULL_DATA返回。