Use an enum class, it's strongly typed but the compiler just treats it as an integer

telling the user to check their manual

• So I made an API for a DB.
• The client was full on using Qt Framework with Qt Creator, so I also made it in Qt.
• I return QSqlError in my functions and point the user to QSqlError documentation in Qt
  • I even show them that they can press F1 at any time in Qt Creator to get the help page
• Months later, client engineers raise problem with senior management that they don't have a bool return value (I am sitting 10m away in the same room as the client. Senior management is in another state)
• I press F1 on their computer and show the user bool QSqlError::isValid()
  • Note again, that all client devs at this point, have been using Qt, years before I enter.
• User says they don't have a bool result.
  • I open their code and show them how to use isValid() in an if statement.
• User puts a requirement for custom functions returning bool
  • I make more functions for that
• Months later, I get a bug report, stating that the deleteDocument function is deleting the document but returning false.
• I check the code

API::deleteDocument(docId);

if (API::deleteDocument(docId))
{
  // output to UI
}

Yes, they called deleteDocument on the same ID twice.

BTW, I did create a manual with usage examples.

A few months later, a senior engineer on the client side checks their code and tells me to throw exceptions for everything, because half of the time, the user-devs are not checking the QSqlError return values.

[[nodiscard]]

From what I remember, that gives a warning an not an error.
The clients' code already has >400 warnings^[edit: fixed wrong word] on every build. They won't care

For fuck's sake people, stop localizing your error messages.

At work we literally just went through this yesterday, just with folly::Expected. A new guy joined the team and wanted to propose we update how we handle errors.