[C++] Problem with SQLBindParameter on IN/OUT parameter

Question

I have the following parameter being bound for calling a SQL procedure:

TCHAR str[41];
SQLINTEGER cb;
SQLBindParameter(hstmt, 1, SQL_PARAM_INPUT_OUTPUT, SQL_C_TCHAR, SQL_C_TCHAR, 40, 0, str, 0, &cb);

When I loop through str after calling the query I can see the result is there, but it's not quite right:

std::stringstream ss;
ss<<"{";
for(int i=0;i<41;++i)
{
    ss<<(int)str[i];
    if(i<40)ss<<',';
}
ss<<"}"<<endl<<"{";
for(int i=0;i<41;++i)
{
    if(str[i])
        ss<<"'"<<str[i]<<"'";
    else
        ss<<"null";
    if(i<40)ss<<',';
}
ss<<"}"<<endl;
cout<<ss.str();

{53,55,56,49,53,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,32,0} {'5','7','8','1','5',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',null}

For whatever reason, str is being padded with spaces. I know the SQL procedure is actually returning "57815" from testing it in isolation. Any ideas what's going on and how to resolve it? The cb value is set to 40 after the SQL call is executed.

Answer 1

If the SQL database field is of type CHAR, it will be space padded (and if it isn't a CHAR, what type is it?). This is expected behaviour. If it isn't are you sure that SQL_C_TCHAR is the type you really want - it isn't listed on this MSDN page.