如何重构C ++代码以支持动态数组大小

Question

I need to get rid of fixed array size in C++/ODBC apps. Instead the hardcoded array size (ROWS =10 below) I want to pass the ROWS as the command-line argument. I know how to parse the command line. But how to adjust the following code?

#define ROWS 10

    SQLINTEGER idata[ROWS]
    SQLCHAR cdata1[ROWS][256]
    SQLFLOAT fdata[ROWS]
    SQL_TIMESTAMP_STRUCT ts[ROWS]

    SQLSetStmtAttr(SQL_ATTR_ROW_ARRAY_SIZE, ROWS)

    SQLBindCol(1, &idata)
    SQLBindCol(2, cdata1)
    SQLBindCol(3, fdata)
    SQLBindCol(4, &ts)
    SQLExecDirect("query producing a result-set")

Update: I cannot modify the signature of SQLBindCol(..)

Let say I will create std::vector instead of SQLFLOAT fdata[ROWS] but how to pass it into SQLBindCol() which does not expect std::vector?

Answer 1

Using std::vector on fdata :

size_t rowCount = /* ... */;
std::vector<SQLFLOAT> fdata(rowCount);
// ...
SQLSetStmtAttr(SQL_ATTR_ROW_ARRAY_SIZE, rowCount);
// ...
SQLBindCol(3, &fdata[0]);
// ...

For cdata1 , std::vector<SQLCHAR> cdata1(250 * rowCount); might work.

Answer 2

I haven't managed to make it work with a 2d dynamic array. But here's a solution for a dynamic 2d array using a 1d array

std::set<std::string> getResults(int columnIndex, HSTMT stmt) {
    std::set<std::string> results;
    RETCODE rc = 0;
    int rows = 250;
    int colsize = 500 + 1; //Need to increment colunm size by 1 because SQLBindCol add the terminator character "\0"

    SQLLEN *indicator1 = new SQLLEN[rows];
    char *buff = new char[rows*colsize];
    SQLSetStmtAttr(stmt, SQL_ATTR_ROW_ARRAY_SIZE, (SQLPOINTER)rows, 0);

    SQLUINTEGER     NumRowsFetched;
    SQLSetStmtAttr(stmt, SQL_ATTR_ROWS_FETCHED_PTR, &NumRowsFetched, 0);

    SQLBindCol(stmt, columnIndex, SQL_C_CHAR, buff, colsize, indicator1);
    while (rc = SQLFetch(stmt) == SQL_SUCCESS) {
        for (int i = 0; (SQLUINTEGER)i < NumRowsFetched; i++) {
            results.insert(&buff[i * colsize]);
        }
    }
    delete[] buff;
    return results;

}

Answer 3

Use pointers.

Accept the ROWS argument from command line as you said. Allocate memory of desired size (ROWS argument that you get) using dynamic memory allocation by using malloc/new to all the variables you have declared like idata, cdata1 etc. That's it!