It looks like you're trying to fetch a Gebruiker record by matching login credentials, but hitting a roadblock with the setString method of PreparedStatement. Let's walk through the most common fixes for this problem:

• Double-check parameter indexing
  MySQL Connector C++ uses 1-based indexing for prepared statement parameters. Your SQL query has two placeholders (?), so make sure you're binding them correctly:

  prep_stmt->setString(1, login); // Binds to the first ? (Gebruiker_login)
  prep_stmt->setString(2, wachtwoord); // Binds to the second ? (Gebruiker_wachtwoord)
  

  Accidentally using 0-based indexing is a super common mistake that breaks parameter binding silently.

• Fix character encoding mismatches
  Since your table and field names use Dutch language characters, there's a good chance encoding mismatches are causing values to not match. First, ensure your connection uses a compatible charset (like utf8mb4 to cover all special characters):

  dbConn->getConnection()->setClientOption("charset", "utf8mb4");
  

  Also verify that the Gebruiker_login and Gebruiker_wachtwoord columns in your database are set to utf8mb4 charset and collation (e.g., utf8mb4_general_ci).

• Add detailed error logging
  Your current code has a try block but no error handling. Catch sql::SQLException to get precise error details—this will tell you exactly if the issue is with binding, permissions, or invalid SQL:

  catch (sql::SQLException &e) {
      std::cerr << "SQL Error Message: " << e.what() << std::endl;
      std::cerr << "MySQL Error Code: " << e.getErrorCode() << std::endl;
      std::cerr << "SQL State: " << e.getSQLState() << std::endl;
      // Clean up resources before returning
      delete res;
      delete prep_stmt;
      return nullptr;
  }
  

• Ensure proper query execution and result handling
  Don't forget to execute the query and move the result set pointer to access the returned row:

  res = prep_stmt->executeQuery();
  if (res->next()) {
      // Populate your Gebruiker object with data from the result set
      gebruiker = new Gebruiker();
      gebruiker->setLogin(res->getString("Gebruiker_login"));
      // Add other field assignments here
  }
  // Always clean up resources to avoid leaks
  delete res;
  delete prep_stmt;
  

  Skipping executeQuery() or res->next() will make it look like setString failed, when in reality the query never ran or you didn't check the results.

• Verify password storage logic
  If your Gebruiker_wachtwoord column stores hashed passwords (e.g., bcrypt, SHA-256), you can't bind the plaintext wachtwoord directly. You need to hash the input password using the same algorithm first, then bind the hashed value to the statement.

内容的提问来源于stack exchange，提问作者DerDerrr