Getting number of columns in a table using ' Proc C-C`` - c++

Question

I am using the below code to get the number of columns in an oracle table.
char selectQuery[30000] = {'\0'};
strcpy(selectQuery, "SELECT COUNT(*) FROM USER_TAB_COLUMNS WHERE TABLE_NAME=\'");
strcat(selectQuery, tableName);
strcat(selectQuery, "\'");
strcpy((char*) stmt.arr, selectQuery);
stmt.len = strlen((char*) stmt.arr );
stmt.arr[stmt.len]= '\0';
EXEC SQL WHENEVER SQLERROR CONTINUE;
EXEC SQL WHENEVER NOT FOUND CONTINUE;
EXEC SQL DECLARE SELECTCOLNU STATEMENT;
EXEC SQL PREPARE SELECTCOLNU FROM :stmt;
if(sqlca.sqlcode != 0)
{
DEBUG_LOG("SQL-ERR:Preparation of SELECT Query to get number of columns failed: Ora-Err: %d %s\n", sqlca.sqlcode, sqlca.sqlerrm.sqlerrmc);
return PREPARATION_FAILURE;
}
EXEC SQL EXECUTE SELECTCOLNU INTO:columnsNo;
if(sqlca.sqlcode < 0)
{
DEBUG_LOG("SQL-ERR:Execute failed: Ora-Err: %d %s\n", sqlca.sqlcode, sqlca.sqlerrm.sqlerrmc);
return EXECTUION_FAILURE;
}
DEBUG_LOG("Number of columns: %d\n", columnsNo);
When I execute the code, It doesn't give any error but I am getting "Number of columns: 0" as the output.
There are few columns in the table I am referring.
Am I doing anything wrong here?
Below is the declaration section...
EXEC SQL BEGIN DECLARE SECTION;
int columnsNo;
VARCHAR stmt[MAX_SQL];
EXEC SQL END DECLARE SECTION;

Answer 1

Don't "escape" the ' in a C- string. It will have \' just in the string, and that is not what you want because the ' is the database string quote, which you now escape for the database and the database doesn't understand the query now.
sprintf(selectQuery, "SELECT COUNT(*) FROM USER_TAB_COLUMNS WHERE TABLE_NAME='%s'", tableName);
Note:
stmt.len = strlen((char*) stmt.arr );
stmt.arr[stmt.len]= '\0';
In the above strlen counts the number of characters until a null character. Thus stmt.arr[stmt.len] is already null. (No harm, though.)