Question

I have this code to open multiple files one at a time that is given at the command line, and then if it cannot open one of the files, it closes all the files and exits.

/* Opens an array of files and returns a pointer to the first 
 * element (the first file).
 */
ifstream *OpenFiles(char * const fileNames[], size_t count)
{
    /* If no command line arguments, error and exit */
    if (count == 0) {
        cerr << "Invalid number of arguments.";
        exit(EXIT_FAILURE);
    }
    ifstream *fileObj;
    fileObj = new ifstream[count];

    if (fileObj == NULL) {
        cerr << "Failed to create space for files";
        exit(EXIT_FAILURE);
    }

    /* Opens one file at a time and closes all files if there is an 
     * error opening any file.
     */
    for (int loopCount = 0; loopCount < (int)count; loopCount++) { 
        fileObj[loopCount].open(fileNames[loopCount], ios::out); 
        if (!fileObj[loopCount].is_open()) { 
            cerr << "Failed to open " << fileNames[loopCount] << "\n";
            for (; loopCount >= 0; loopCount--) {
                fileObj[loopCount].close();
                cout << "Closed " << fileNames[loopCount] << "\n";
            }
            delete[] fileObj;
        } 
    }
    return fileObj;
}

I am doing this for homework and my teacher has another checker we have to submit to and gives me these types of warnings:

Assign8_1.cpp(44): error 445: (Warning -- Reuse of for loop variable 'loopCount' at 'line 40' could cause chaos)
    return fileObj;
Assign8_1.cpp(51): error 850: (Info -- for loop index variable 'loopCount' whose type category is 'integral' is modified in body of the for loop that began at 'line 40')
    return fileObj;
Assign8_1.cpp(51): error 449: (Warning -- Pointer variable 'fileObj' previously deallocated [Reference: file Assign8_1.cpp: lines 30, 48])
Assign8_1.cpp(30): error 831: (Info -- Reference cited in prior message)
Assign8_1.cpp(48): error 831: (Info -- Reference cited in prior message)
}
Assign8_1.cpp(63): error 818: (Info -- Pointer parameter 'files' (line 55) could be declared as pointing to const)
}

Starting with the first warning, I was wondering why I shouldn’t use my loopCount variable twice the way I do in my code. That was the way I thought it would work, keeping track of which file I am looking at, opening, and closing it appropriately.

Does anyone know what error 449 means? Thanks.

Answer 1

You need to exit(EXIT_FAILURE) after you delete[] fileObj in the loop, otherwise you’ll simply crash on the next iteration. That may be what warning 449 is telling you.

Other than that, the code looks fine. If you want it to compile without those warnings, though, you could turn the inner loop into a standard for-loop which only uses loopCount as a bound. Something like:

for (int i = loopCount; i >= 0; i--) {
    fileObj[i].close();
    cout << "Closed " << fileNames[i] << "\n";
}