To repeat:

1. Create procedure:

create procedure p1(in username varchar(192))
begin
declare temphost varchar(16);
declare hosts varchar(255);
declare nomore int;

declare curuser cursor for select host from mysql.user where user=username;
declare continue handler for not found set nomore=1;

set hosts='';
set nomore=0;

open curuser;
fetch curuser into temphost;
while nomore <> 1 do
set hosts = concat(hosts, temphost);
fetch curuser into temphost;
if nomore <> 1 then
set hosts = concat(hosts, "\n");
end if;
end while;
close curuser;

if hosts <> '' then
select user, hosts from mysql.user where user=username;
end if;
end

2. Compile and run following code:

#include <stdlib.h>
#include <iostream>
#include <sstream>
#include <stdexcept>
#include <string>
	
#include "mysql_connection.h"
	
#include <cppconn/driver.h>
#include <cppconn/exception.h>
#include <cppconn/resultset.h>
#include <cppconn/statement.h>
#include <cppconn/prepared_statement.h>
	
#define EXAMPLE_HOST "tcp://127.0.0.1:13000"
#define EXAMPLE_USER "root"
#define EXAMPLE_PASS ""
#define EXAMPLE_DB "test"
	
using namespace std;
	
int main(int argc, const char **argv)
{	

    string url(argc >= 2 ? argv[1] : EXAMPLE_HOST);
    const string user(argc >= 3 ? argv[2] : EXAMPLE_USER);
    const string pass(argc >= 4 ? argv[3] : EXAMPLE_PASS);
    const string database(argc >= 5 ? argv[4] : EXAMPLE_DB);

    std::auto_ptr< sql::PreparedStatement >  pstmt;
    std::auto_ptr< sql::ResultSet > res;
	
		sql::Driver* driver = get_driver_instance();
		std::auto_ptr<sql::Connection> con(driver->connect(url, user, pass));
		con->setSchema(database);
		//std::auto_ptr<sql::Statement> stmt(con->createStatement());
		
		pstmt.reset(con->prepareStatement("CALL p1('root')"));
		pstmt->executeQuery();
		res.reset(pstmt->getResultSet());
		
		if (res->next()) {
			cout << res->getString("hosts");
		}
    cout << "Done." << endl;
    return EXIT_SUCCESS;
}

3. Procedure without cursor that works:

create procedure p4(in username varchar(192))
begin
declare temphost varchar(16);
declare hosts varchar(255);
declare nomore int;

declare curuser cursor for select host from mysql.user where user=username;
declare continue handler for not found set nomore=1;

set hosts='foo';
set nomore=0;



if hosts <> '' then
select user, hosts from mysql.user where user=username;
end if;
end