SQLGETDATA使用C++和SQL本地客户端发布 我有一个C++应用程序，它使用SQL本地客户端连接到MS SQL Server 2000。

我试图从包含比最初分配给它的缓冲区提供的数据更多的文本列中检索结果。为了澄清我的问题，我将在下面概述我在做什么：

分配1024字节的缓冲区以供使用 使用SQLBindColumn将缓冲区绑定到列 使用SQLExecute执行SELECT查询 使用SQLFetch遍历结果 SQLFetch无法将整个结果返回到我的缓冲区：我想使用SQLGetData检索整个列值 上面的操作顺序提出了一个问题：SQLGetData在我的驱动程序中的绑定列上不起作用

一个有效的解决方案是使用SQL_DATA_AT_EXEC标志，如下面的代码所示

开始代码：

#include <windows.h>

#include <sql.h>
#include <sqlext.h>
#include <sqltypes.h> 
#include <sqlncli.h>

#include <cstdio>
#include <string>

const int MAX_CHAR = 1024;

bool test_retcode( RETCODE my_code, const char* my_message )
{
    bool success = ( my_code == SQL_SUCCESS_WITH_INFO || my_code == SQL_SUCCESS );
    if ( ! success )
    {
        printf( "%s", my_message );
    }

    return success;
}

int main ( )
{
    SQLHENV EnvironmentHandle;

    RETCODE retcode = SQLAllocHandle( SQL_HANDLE_ENV, SQL_NULL_HANDLE, &EnvironmentHandle );
    test_retcode( retcode, "SQLAllocHandle(Env) failed!" );

    retcode = SQLSetEnvAttr( EnvironmentHandle, SQL_ATTR_ODBC_VERSION, (SQLPOINTER) SQL_OV_ODBC3, SQL_IS_INTEGER );
    test_retcode( retcode, "SQLSetEnvAttr(ODBC version) Failed" );

    SQLHDBC ConnHandle;
    retcode = SQLAllocHandle( SQL_HANDLE_DBC, EnvironmentHandle, &ConnHandle );
    test_retcode( retcode, "Could not allocate MS SQL 2000 connection handle." );

    SQLSMALLINT driver_out_length;
    retcode = SQLDriverConnect( ConnHandle,
        NULL, // we're not interested in spawning a window
        (SQLCHAR*) "DRIVER={SQL Native Client};SERVER=localhost;UID=username;PWD=password;Database=Test;",
        SQL_NTS,
        NULL,
        0,
        &driver_out_length,
        SQL_DRIVER_NOPROMPT );
    test_retcode( retcode, "SQLConnect() Failed" );

    SQLHSTMT StatementHandle;
    retcode = SQLAllocHandle(SQL_HANDLE_STMT, ConnHandle, &StatementHandle);
    test_retcode( retcode, "Failed to allocate SQL Statement handle." );

    char* buffer = new char[ MAX_CHAR ];
    SQLINTEGER length = MAX_CHAR - 1;

    // -- Bind Block
    retcode = SQLBindCol( StatementHandle, 
        1,
        SQL_C_CHAR,
        (SQLPOINTER) NULL,
        (SQLINTEGER) SQL_DATA_AT_EXEC,
        &length );

    test_retcode( retcode, "Failed to bind column." );
    // -- End Bind Block

    retcode = SQLExecDirect( StatementHandle, (SQLCHAR*) "SELECT VeryLong FROM LongData", SQL_NTS );
    test_retcode( retcode, "SQLExecDirect failed." );

    // -- Fetch Block
    retcode = SQLFetch( StatementHandle );
    if ( retcode != SQL_SUCCESS && retcode != SQL_SUCCESS_WITH_INFO && retcode != SQL_NO_DATA )
    {
        printf( "Problem fetching row.\n" );
        return 9;
    }

    printf( "Fetched data.  length: %d\n", length );
    // -- End Fetch Block


    bool sql_success;
    std::string data;
    RETCODE r2;
    do
    {
        r2 = SQLGetData( StatementHandle, 1, SQL_C_CHAR, buffer, MAX_CHAR, &length );

        if ( sql_success = test_retcode( r2, "SQLGetData failed." ) )
        {
            data.append( buffer );
        }
        else
        {
            char* err_msg = new char[ MAX_CHAR ];
            SQLSMALLINT req = 1;
            SQLCHAR state[6];
            SQLINTEGER error;
            SQLINTEGER output_length;

            int sql_state = SQLGetDiagRec( SQL_HANDLE_STMT, StatementHandle, req, state, &error, (SQLCHAR*) err_msg, (SQLINTEGER) MAX_CHAR, (SQLSMALLINT*) &output_length );

            // state is: 07009, error_msg: "[Microsoft][SQL Native Client]Invalid Descriptor Index"
            printf( "%s\n", err_msg );

            delete err_msg;

            return 9;
        }
    } 
    while ( sql_success && r2 != SQL_SUCCESS );

    printf( "Done.\n" );

    return 0;
}

尝试将SQLBindCol放在SQLExecDirect之后

供文本列使用

retcode=SQLBindCol语句句柄，1，SQL\u C\u CHAR， SQLPOINTER NULL，SQLINTEGER SQL\U DATA\U AT\U EXEC，&length

---

通过这种方式，您可以重复SQLGetData以多个片段读取整个文本数据

我继续在SQLExecDirect之前调用SQLBindCol，但正如您所演示的那样，我使用了SQL_data_AT_EXEC length指示符，它工作得非常出色。我将修改代码块以显示我的新方法。