I would like to know how to change the name of a file that has already a fixed default name in the main().

As you can see in the main, the name of the file is already set to movies.dat (char dateiname[50] ="movies.dat") and I would like to change that with case 'd' that goes to the function "dateiUmbenennen()". Also the changed name should be used everywhere where I used "dateiname".

Any help would be nice!

This is my code so far:

int
dateiUmbenennen(char* pdateiname)
{
    char newName[50];

    printf("Bitte geben Sie den neuen Namen mit gewuenschtem Dateitypen ein: ");
    scanf("%s", &newName);

    int res = rename(pdateiname, newName);
    if (!res)
    {
        printf("Datei wurde erfolgreich in %s umbenannt!\n", newName);
        *pdateiname = newName[50];
    }
    else
    {
        printf("ERROR: Umbenennung fehlgeschlagen mit dem Fehler: %s!\n", strerror(errno));
    }
    return 0;
}

// ================================================================
// MAIN
// ================================================================

int main(void)
{
    // Default fuer Namen der Filmdatei
    char dateiname[50]= "movies.dat";

    // Hilfsvariablen-------------------------------------------------------------------------------------------------


    // Hilfsvariable fuer do-while-Schleife
    int stopLoop = 0;

    // Hauptschleife
    do {
        // Ausgabe des Bildschirm-Menus
        printf("\nAUSWAHL-MENU:\n");
        printf("(n)   Neuen Film eingeben\n");
        printf("(a)   Alle Filme anzeigen lassen\n");
        printf("(o)   Filmdatenbank aus Datei einlesen\n");
        printf("(s)   Filmdatenbank in Datei speichern\n");
        printf("(d)   Dateinamen fuer Lesen/Speichern festlegen (Aktuell: %s)\n",
            dateiname);
        printf("(q)   Programm verlassen\n");
        //printf("\nIhre Wahl: ");

        // Abfrage der Benutzerwahl
        char ch = _getch();
        printf("%c\n\n", ch);

        // Aktionen in Abhaengigkeit von der Benutzerwahl
        switch (ch)
            //----------------------------------------------------------------------------------------------------------------------
        {
        case 'q': // Programm verlassen
            stopLoop = 1;
            break;
        case 'n': // Neuen Film eingeben
            movieDatensatz = benutzerEingabe();
            break;
        case 'a': // Alle Filme anzeigen lassen
            konsolenAusgabe(movieDatensatz, anzahlFilme=dateiEinlesen(dateiname));
            break;
        case 'o': // Filmdatenbank aus Datei einlesen
            dateiEinlesen(dateiname);
            break;
        case 's': // Filmdatenbank in Datei speichern
            break;
        case 'd': // Dateinamen fuer Lesen/Speichern festlegen
            dateiUmbenennen(&dateiname[50]);
            break;
        case 'h':
            printf("%s", dateiname);
            break;
        default:  // keine gueltige Eingabe
            printf("==> Ungueltige Eingabe!\n");
        }

    } while (!stopLoop);

    return 0;
}

CodePudding user response：

If you want the function dateiUmbenennen to change the contents of the array dateiname in the function main, then, when calling the function dateiUmbenennen from main, you should pass a pointer to that array.

You seem to be attempting to do exactly that in the line

dateiUmbenennen(&dateiname[50]);

However, this is passing the address of the 51^st element of that array (which does not even exist, because the array only has 50 elements) to the function. This does not make sense. You should instead pass the address of the start of the array, i.e. the address of the 1^st element. You can do it like this:

dateiUmbenennen( &dateiname[0] );

However, it is more common to simply write

dateiUmbenennen( dateiname );

as using the array in this context will cause the array to automatically decay to a pointer to the first element.

The line

*pdateiname = newName[50];

also does not make sense, as that line copies the (non-existant) 51^st element of the array newName to whatever pdateiname is pointing to (which should be the start of dateiname, but is not in your posted code). Assuming that pdateiname is pointing to the start of dateiname, then you can copy the whole string using the function strcpy, like this:

strcpy( pdateiname, newName );

Also, I recommend that you change the line

scanf("%s", &newName);

to

scanf("Is", &newName);

so that if the user enters more than 49 characters, you will not overflow the newName array.

CodePudding user response：

The line

*pdateiname = newName[50];

doesn't really make any sense -- it reads an invalid location (newName[50] is past the end of the array) and copies a single character. What you probably meant to do is

strcpy(pdateiname, newName);

to copy the string from the newName array to the pdateiname array.