Mysql_num_rows() Segfaults - c++

Question

I'm writing a program using C++ and the MySQL C API (version 5.1.31 ubuntu2). However, if the query is UPDATE then I get a Segmentation Fault error when executing the line "RowsReturned = mysql_num_rows( Result );".
//this code snippet contains only the relevant code
MYSQL_RES *Result;
long RowsReturned;
MYSQL_RES *MYSQLDB::RunQuery( const char* Query )
{
if( mysql_query( Connection, Query) )
{
std::cout << "Error: " << mysql_error( Connection );
exit(1);
}
Result = mysql_store_result( Connection );
RowsReturned = mysql_num_rows( Result );
return Result;
}
Compiled using g++ 4.3.3 (g++ test.cpp -I/usr/include/mysql -L/usr/lib/mysql -lmysqlclient_r -o Test)
Thanks in advance.
//this snippet contains the entire class code
class MYSQLDB
{
public:
void Connect( const char* DB );
MYSQL_RES *RunQuery( const char* Query );
long NumRows();
void Close();
MYSQL_ROW GetRow();
private:
MYSQL *Connection;
MYSQL_RES *Result;
MYSQL_ROW Row;
long RowsReturned;
};
void MYSQLDB::Connect( const char* DB )
{
Connection = mysql_init( NULL );
if( Connection == NULL )
{
std::cout << "Error: " << mysql_error( Connection );
exit( 1 );
}
if ( mysql_real_connect( Connection, "localhost", "root", "password", DB, 0, NULL, 0 ) == NULL)
{
std::cout << "Error: " << mysql_error( Connection );
exit(1);
}
}
MYSQL_RES *MYSQLDB::RunQuery( const char* Query )
{
if( mysql_query( Connection, Query) )
{
std::cout << "Error: " << mysql_error( Connection );
exit(1);
}
Result = mysql_store_result( Connection );
RowsReturned = (long)mysql_num_rows( Result ); //ERROR!!!!!!!
return Result;
}
long MYSQLDB::NumRows()
{
return RowsReturned;
}
void MYSQLDB::Close()
{
mysql_free_result( Result );
mysql_close( Connection );
}
MYSQL_ROW MYSQLDB::GetRow()
{
return mysql_fetch_row( Result );
}

Answer 1

From the mysql documentation:
mysql_store_result() returns a null pointer if the statement didn't return a result set (for example, if it was an INSERT statement).
You are updating so you have a NULL as results.
Try something like this:
Result = mysql_store_result( Connection );
if (Result) {
RowsReturned = mysql_num_rows( Result );
} else {
RowsReturned = 0;
}