无法在mysql中使用insert语句

Question

void database::adduser(std::string username, std::string password, std::string land){
  connect();
  mysql_query(con, "USE users");
  std::stringstream ss;
  ss << "INSERT INTO users (username, paswd, land, landx, landy) VALUES (" << "'" << username << "'" << "," << "'" << password <<"'" << "," << "'" << land << "'"<< "50, 50)";
  std::string insert;
  insert = ss.str();
  const char * c = insert.c_str();
  mysql_query(con, c);
  mysql_close(con);
}
int database::init(){
  connect();
  mysql_query(con, "USE users");
  mysql_query(con, "CREATE TABLE IF NOT EXISTS users(username TEXT, passwd TEXT, land TEXT, landx INT, landy INT)");

  mysql_close(con);
  return 0;
}
char* database::getpaswd(std::string username){
  connect();
  mysql_query(con, "USE users");
  std::stringstream ss;
  ss << "SELECT paswd FROM users WHERE username=" << "'" << username << "'";
  std::string insert;
  insert = ss.str();
  const char * c = insert.c_str();
  mysql_query(con, c);
  MYSQL_RES *result;
  result = mysql_store_result(con);
  MYSQL_ROW row;
  row = mysql_fetch_row(result);
  if(row == NULL){
    std::cout << "NO USER OF THAT USERNAME" << std::endl;
    return "NOT VALID USERNAME";
  }
  mysql_free_result(result);
  mysql_close(con);
  return row[0];
}
bool database::does_exist_user(std::string user){
  connect();
  mysql_query(con, "USE users");
  std::stringstream ss;
  ss << "SELECT username FROM users WHERE username=" << "'" << user << "'";
  std::string insert;
  insert = ss.str();
  const char *c = insert.c_str();
  mysql_query(con, c);
  MYSQL_RES *result;
  result = mysql_store_result(con);
  MYSQL_ROW row;
  row = mysql_fetch_row(result);
  if(row == NULL){
    mysql_free_result(result);
    return false;
  }
  else{
    mysql_free_result(result);
    return true;
  }
  std::cout << "username taken" << std::endl;
  return true;
}
void database::edit_land(std::string username, std::string land){
  connect();
  mysql_query(con, "USE users");
  std::stringstream ss;
  ss << "UPDATE users SET land=" << "'" << land << "' " << "WHERE username=" << "'" << username << "'";
  std::string insert;
  insert = ss.str();
  const char *c = insert.c_str();
  mysql_query(con, c);
  mysql_close(con);
}
void database::edit_landX(std::string username, int land){
  connect();
  mysql_query(con, "USE users");
  std::stringstream ss;
  ss << "UPDATE users SET landx=" << land << " WHERE username=" << "'" << username << "'";
  std::string insert;
  insert = ss.str();
  const char *c = insert.c_str();
  mysql_query(con, c);
  mysql_close(con);
}
void database::edit_landY(std::string username, int land){
  connect();
  mysql_query(con, "USE users");
  std::stringstream ss;
  ss << "UPDATE users SET landy=" << land << " WHERE username=" << "'" << username << "'";
  std::string insert;
  insert = ss.str();
  const char *c = insert.c_str();
  mysql_query(con, c);
  mysql_close(con);
}
char* database::getland(std::string username){
  connect();
  mysql_query(con, "USE users");
  std::stringstream ss;
  ss << "SELECT land FROM users WHERE username=" << "'" << username << "'";
  std::string insert;
  insert = ss.str();
  const char *c = insert.c_str();
  mysql_query(con, c);
  MYSQL_RES *result;
  result = mysql_store_result(con);
  MYSQL_ROW row;
  row = mysql_fetch_row(result);
  if(row == NULL){
    return "ERROR";
  }
  mysql_close(con);
  mysql_free_result(result);
  return row[0];
}
char* database::getlandY(std::string username){
  connect();
  mysql_query(con, "USE users");
  std::stringstream ss;
  ss << "SELECT landy FROM users WHERE username=" << "'" << username << "'";
  std::string insert;
  insert = ss.str();
  const char *c = insert.c_str();
  mysql_query(con, c);
  MYSQL_RES *result;
  result = mysql_store_result(con);
  MYSQL_ROW row;
  row = mysql_fetch_row(result);
  if(row == NULL){
    std::cout << "ERROE ME BOI" << std::endl;
    return "ERROR";
  }
  mysql_close(con);
  mysql_free_result(result);
  return row[0];
}
char* database::getlandX(std::string username){
  connect();
  mysql_query(con, "USE users");
  std::stringstream ss;
  ss << "SELECT landx FROM users WHERE username=" << "'" << username << "'";
  std::string insert;
  insert = ss.str();
  const char *c = insert.c_str();
  mysql_query(con, c);
  MYSQL_RES *result;
  result = mysql_store_result(con);
  MYSQL_ROW row;
  row = mysql_fetch_row(result);
  if(row == NULL){
    std::cout << "ERROE ME BOI" << std::endl;
    return "ERROR";
  }
  mysql_close(con);
  mysql_free_result(result);
  return row[0];
}
void database::connect(){
  con = mysql_init(NULL);

  if(con == NULL){
    std::cout << mysql_error(con) << std::endl;
    exit(1);
  }

  if(mysql_real_connect(con, "127.0.0.1", "root", "password", "users", 3306, NULL, 0) == NULL){
    std::cout << "NO BEUNO";
    std::cout << mysql_error(con) << std::endl;
    exit(1);
  }
}

问题是我无法使用create user函数，但是从数据库中读取的所有其他函数都可以正常工作，所以我的问题是为什么我无法在程序中使用插入语句但是我能够从数据库中读取。它适用于终端，我使用mysql -u root -p在终端上输入mysql，但是当运行它时，它不起作用。