Calling stored procedure with CURSOR_TYPE_READ_ONLY causes error "Commands out of sync"

#include <mysql.h>

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

int main(int argc, char **argv)

{

  unsigned int port= 3306;

  if (argc > 1)

    sscanf(argv[1], "%d", &port);

  MYSQL *con = mysql_init(NULL);

  if (mysql_real_connect(con, "127.0.0.1", "root", "", "test", port, NULL, 0) == NULL)

  {

    fprintf(stderr,"Can't connect: %s\n",mysql_error(con));

    exit(1);

  }

  mysql_query(con,"drop procedure if exists sp");

  mysql_query(con,"create procedure sp() select 1");

  MYSQL_STMT *stmt = mysql_stmt_init(con);

  unsigned long cursor = CURSOR_TYPE_READ_ONLY;

  const char* query= "call sp()";

  if (mysql_stmt_prepare(stmt,query,strlen(query)))

  {

    fprintf(stderr,"Couldn't prepare: %s\n", mysql_error(con));

    mysql_close(con);

    exit(1);

  }

  mysql_stmt_attr_set(stmt, STMT_ATTR_CURSOR_TYPE, &cursor);

  if (mysql_stmt_execute(stmt))

    fprintf(stderr,"Got error: %s\n", mysql_stmt_error(stmt));

  mysql_stmt_close(stmt);

  mysql_close(con);

  exit(0);

}

Got error: Commands out of sync; you can't run this command now