C++ Error: Wunused-but-set-variable

Question

I get the error I mentioned in the title when I try to compile the following code:

void Sql::select(const string table, const string column, const string condition, const string condition_2, const string condition_3) {
otl_stream s;
otl_column_desc* desc;
int desc_len;

const string select = str(format("SELECT %2% FROM %1% WHERE LEFT(%3%, 8) < %6% AND %4% = 'Ausstehend' AND (%5% = '1' OR %5% = '2') ")
        % table % column % condition % condition_2 % condition_3 % getDate());

// cout << select;
    try {
        s.open(10, select.c_str(), con);
    } catch (otl_exception &e) {
        cerr << e.msg;
    }

desc = s.describe_select(desc_len);

}

I am told that otl_column_desc* desc is set but not used. Can you tell me what goes wrong there?

Answer 1

Its exactly what it says, you are setting the variable but not using the value anywhere, meaning this variable is, for all intents and purposes, useless.

desc = s.describe_select(desc_len);//value in desc never used

This sometimes could happen if you make a mistake in your code, and use some other variable when you meant to use this one, and I guess this warning is to catch those cases.

But to answer your question, nothing is wrong since this is a warning, not an error. It is just an indication that something might be wrong.