问为什么SQLconnect返回一个SQL_ERROR，SQLGetDiagRec却没有显示任何信息？

#include<stdio.h> 
#include<windows.h> 
#include<sql.h> 
#include<sqlext.h> 
#include<sqltypes.h> 
#include<sqlucode.h>
#include<string>
#include<iostream>
using namespace std;

int main()
{
	SQLRETURN ret;
	SQLHENV henv;//环境句柄
	SQLHDBC hdbc;//连接句柄
	SQLHSTMT hstmt;//语句句柄
	
	ret = SQLAllocHandle(SQL_HANDLE_ENV, NULL, &henv);//申请环境句柄 
	ret = SQLSetEnvAttr(henv, SQL_ATTR_ODBC_VERSION, (SQLPOINTER)SQL_OV_ODBC3_80, SQL_IS_INTEGER);//设置环境属性 
	ret = SQLAllocHandle(SQL_HANDLE_DBC, henv, &hdbc);//申请数据库连接句柄 
	ret = SQLConnect(hdbc, (SQLWCHAR*)"myTest", SQL_NTS, (SQLWCHAR*)"sa", SQL_NTS, (SQLWCHAR*)"1234", SQL_NTS);//连接数据库 
	if (ret != SQL_SUCCESS){
	        SQLINTEGER   NumRecords = 0;
                SQLGetDiagField( SQL_HANDLE_DBC, 
                                              hdbc, 
                                              0,
                                              SQL_DIAG_NUMBER,
                                              &NumRecords,
                                              SQL_IS_INTEGER,
                                              NULL );
	        printf("Total Number of diagnostic records: %d\n", NumRecords);	

	        SQLSMALLINT   Counter = 0;
	        SQLINTEGER     NativeErr = 0;
	        SQLWCHAR      SQLState[6];
	        SQLWCHAR      ErrMsg[255];
	        SQLSMALLINT  ErrMsgLen = 0;

	        for (Counter = 1; Counter <= NumRecords; Counter++)
	        {
		  SQLGetDiagRec( SQL_HANDLE_DBC, 
                                              hdbc, 
                                              Counter,
                                              SQLState, 
                                              &NativeErr, 
                                              ErrMsg, 
                                              sizeof(ErrMsg),
                                              &ErrMsgLen  );
		  printf("SQLSTATE : %s\n", SQLState);
		  printf("%s\n", ErrMsg);
	        }
	}
	return 0;
}

SQLConnect(hdbc, (SQLWCHAR*)"myTest"——> myTest是一个没有在ODBC注册的数据源