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switch (file.Error())
{
case FileNotFound: //...
case FileLocked: //...
case FileAccessNotPermitted: //...
}

Gigasoft wrote:I think //... is the important part here.

retry:
    status = file.Error();
    switch (status)
    {
        case OK:
            break;
        case FileNotFound:
            create_default_file();
            goto retry;
        case FileLocked:
            sleep(2);          /* Wait for other process to finish using it */
            goto retry;
        case FileAccessNotPermitted:
            do_dialog_box("ERROR: File permission problem.");
            exit(1);
        default:
            do_dialog_box("ERROR: An unknown error (%s) occurred while trying to write to the log file", system.getErrorString(status) );
            exit(1);
    }

Gigasoft wrote:It usually doesn't matter to an application how something went wrong - there is nothing it can do about it anyway.

    printf("Please remove the CD-ROM!");
    do {
        status = open("/dev/cd");
        switch(status) {
        OK:
            /* "OK" is an error (CD not removed) */
            close("/dev/cd");
        ....
    } while(status != NO_MEDIA);      /* "No media error" indicates everything is OK (CD-ROM successfully removed) */

Gigasoft wrote:As for receipt printers, they normally don't return error codes. Instead, they report their status when there is a change or when requested by the user, so it doesn't make sense for the system to make up an error code.

Gigasoft wrote:I am guessing that regardless of what the problem is, it is handled by displaying something like "Out of order - Please contact the staff" on the screen and halting.

Gigasoft wrote:

switch (file.Error())
{
case FileNotFound: //...
case FileLocked: //...
case FileAccessNotPermitted: //...
}

I think //... is the important part here. It usually doesn't matter to an application how something went wrong - there is nothing it can do about it anyway. Either the hardware malfunctioned, or the programmer made a mistake. If the programmer made a mistake, he should have discovered it during testing. If a piece of the hardware has malfunctioned, it should be obvious to customer support after some investigation.

Gigasoft wrote:As for receipt printers, they normally don't return error codes. Instead, they report their status when there is a change or when requested by the user, so it doesn't make sense for the system to make up an error code. I am guessing that regardless of what the problem is, it is handled by displaying something like "Out of order - Please contact the staff" on the screen and halting.

rdos wrote:

Gigasoft wrote:

switch (file.Error())
{
case FileNotFound: //...
case FileLocked: //...
case FileAccessNotPermitted: //...
}

That's my point. You shouldn't surround every syscall with massive error decoding and recovery. Errors that are important instead should be possible to read-out on demand as device-status.

#define SYSCALL_FAILED(code) ((code)<0)
if ( SYSCALL_FAILED(err = file.Error()) ) {
  I_dont_care_just_panic();
}

OR:


if ( SYSCALL_FAILED(err = file.Error()) ) {
  switch ( err ) {
  case FileNotFound:
      ...
  default:
      unknown_error();
  }
}

Solar wrote:If you "correct" perfectly-good pseudocode into (pseudo-) source, don't selectively disable your brain (*), and at least use a somewhat-correct syntax, will you?

Code: Select all

    int rc = do( X );
    if ( rc == 0 )
        rc = do( Y );

    switch ( rc )
    {
        case 0:
            break;
        case a:
            handleError_A();
            break;
        case b:
            handleError_B();
            break;
        default:
            unexpectedError( rc );
            break;
    }

vs.

Code: Select all

    bool rc = do( X );
    if ( rc )
        rc = do( Y );

    if ( ! rc )
    {
        if ( isErrorA() )
            handleError_A();
        else if ( isErrorB() )
            handleError_B();
        else
            unexpectedError();
    }

    bool rc = do( X );
    if ( rc )
        rc = do( Y );

    bool rc = do( X );
    if (!rc)
       log("X failed");
    if ( rc )
    {
        rc = do( Y );
        if (!rc)
            log("Y failed");
    }

bluemoon wrote: This is common to do:

Code: Select all

#define SYSCALL_FAILED(code) ((code)<0)
if ( SYSCALL_FAILED(err = file.Error()) ) {
  I_dont_care_just_panic();
}

OR:


if ( SYSCALL_FAILED(err = file.Error()) ) {
  switch ( err ) {
  case FileNotFound:
      ...
  default:
      unknown_error();
  }
}

Griwes wrote:rdos, you are wrong. Sometimes the application wants to show user a message, like in Brendan's version of my simple code. And wait, you want the user to have to trace the syscall to the kernel, even if the problem was a simple "file not found".

Griwes wrote:But, because you again don't even try to read those important parts of posts, where it's explained why polling different statuses simply fail to work (and we already showed two of them), I must assume you are just trolling and knowing that, I am leaving this thread.

Griwes wrote:rdos, in post above my previous one, you mentioned embedded applications. But again, not mentioning embedded applications anywhere before.

Solar wrote:

Griwes wrote:rdos, in post above my previous one, you mentioned embedded applications. But again, not mentioning embedded applications anywhere before.

That's not quite correct; he did mention "embedded" before. But even on an embedded system not returning the error code has no advantages and several disadvantages.

Not that he would ever admit that.

rdos wrote:Griwes, I didn't say anything was superior.

rdos wrote:Traditional APIs (like DOS, Windows and *nix) are cluttered with error-codes, but is this really necesary? Isn't error-codes just a bagage from non-object oriented designs that are not really necesary?