C++ assign variable value from SQL Server SELECT - c++

Question

I've got a script that does a bunch of SQL inserts but I've been trying to add a section that assigns the returned value of a select query into a variable.
The code I've been using to do the inserts is:
if (SQL_SUCCESS != SQLExecDirect(sqlstatementhandle, (SQLCHAR*)"BULK INSERT mytable FROM 'C:/dir/myfile.csv' WITH (FIRSTROW = 1, FIELDTERMINATOR = ',', ROWTERMINATOR = '\n');", SQL_NTS)) {
show_error(SQL_HANDLE_STMT, sqlstatementhandle);
That all works fine, but I can't figure out how to use the output of a query. The output will be a single int value, which I'd like to assign to an int variable.
Apologies if this is something that's blindingly obvious.
EDIT
Based on the answer below, the following has now worked for me. Thanks!
SQLRETURN retcode;
SQLHSTMT hstmt; // I use my own stmnthndl(sqlstatementhandle) below, this line left in for demonstration
retcode = SQLExecDirect(sqlstatementhandle, (SQLCHAR*)"SELECT count(*) FROM mytable;",SQL_NTS);
SQLINTEGER sCustID;
SQLLEN cbCustID;
if (retcode == SQL_SUCCESS) {
while (TRUE) {
retcode = SQLFetch(sqlstatementhandle);
if (retcode == SQL_SUCCESS || retcode == SQL_SUCCESS_WITH_INFO) {
// get the first column
SQLGetData(sqlstatementhandle, 1, SQL_C_ULONG, &sCustID, 0, &cbCustID);
//You can now print it
cout << "CustID:" << sCustID;
}
else {
break;
}
}
}

Answer 1

You can use SQLGetData to get the data for a single column in the resultset. Taken from this example, first you execute the SQL query with SQLExecDirect:
SQLRETURN retcode;
SQLHSTMT hstmt;
retcode = SQLExecDirect(hstmt,
(SQLCHAR*)"SELECT CUSTID, NAME, PHONE FROM CUSTOMERS ORDER BY 2, 1, 3",
SQL_NTS);
Then you can get the data, I show a reduced version of the same example:
SQLINTEGER sCustID, cbCustID;
if (retcode == SQL_SUCCESS) {
while (TRUE) {
retcode = SQLFetch(hstmt);
if (retcode == SQL_ERROR || retcode == SQL_SUCCESS_WITH_INFO) {
show_error();
}
if (retcode == SQL_SUCCESS || retcode == SQL_SUCCESS_WITH_INFO){
// get the first column
SQLGetData(hstmt, 1, SQL_C_ULONG, &sCustID, 0, &cbCustID);
//You can now print it
fprintf(out, "CustID: %-5d", sCustID);
} else {
break;
}
}
}
The syntax of SQLGetData is:
SQLRETURN SQLGetData(
SQLHSTMT StatementHandle,
SQLUSMALLINT Col_or_Param_Num,
SQLSMALLINT TargetType,
SQLPOINTER TargetValuePtr,
SQLLEN BufferLength,
SQLLEN * StrLen_or_IndPtr);
With:
StatementHandle: the handle to the executed SQL query.
Col_or_Param_Num: the column number, which starts at 1.
TargetType: the data type, you can probably use SQL_INTEGER, see SQL data types and C data types.
TargetValuePtr: the pointer to the output data.
BufferLength: the length, but is not used for fixed length data such as integers.
StrLen_or_IndPtr: an optional output that can return the length of the data or an error code.
Note: like you commented you might need to cast the SQL query to SQLCHAR * since SQLCHAR is an unsigned char, see the data types.