Cannot Delete a pointer array inside a stuct pointer (c++)

Question

Im having trouble with the syntax here. We are studying structures and pointers in class currently and are tasked with creating a dynamic array of a single structure with a pointer array inside to both be allocated and deleted by the end of the program. (Hopefully that made sense)

Here are the snippits of code im working with, note how the entry of scores works:

std::cin << stuArray[i].stuScore[j]

But then the deletion in a similar manner, does not:

delete[] stuArray[count].stuScore[j];

Deletion Code:

    do
{
    for (unsigned short j = 0; j < numTests; j++)
    {
        delete[] stuArray[count].stuScore[0]; //Syntax???????
    }
    count++;
} while (count < numStudents);
delete[] stuArray;

Score Entry Code (Which Works)

bool ScoreEntry(Student * stuArray, unsigned short numStudents, unsigned short numTests)
{
    //Local Variables
    unsigned short idTempChoice = 0;

    //Get Id Number
    std::cout << "\nChoose a student by ID and enter the test scores: ";
    std::cin >> idTempChoice;

    //Id lookup
    for (unsigned short i = 0; i < numStudents; i++)
    {
        //Id Check
        if (idTempChoice == stuArray[i].stuId)
        {
            std::cout << "Student selected: " << stuArray[i].stuName << std::endl;

            //Score Entry
            for (unsigned short j = 0; j < numTests; j++)
            {
                std::cout << "Test " << j + 1 << "'s Score: ";
                std::cin >> stuArray[i].stuScore[j];
            }//End For Loop j

            return true;
        }
    }//End For Loop i

    //Student Id not found
    std::cout << "Student not found!\n";
    return false;
}

Allocation Code (Struct):

void MemAllocation(Student * &stuArray, unsigned short &numStudents)
{
    //Get Number of students
    std::cout << "How many students have taken the test: ";
    std::cin >> numStudents;
    std::cout << std::endl;

    //Dynamically allocate pointers
    stuArray = new Student[numStudents];
}

Allocation Code (Pointer inside struct):

for (unsigned short i = 0; i < numTests; i++) //Allocate Dynamic array for each student
    {
        stuArray[i].stuScore = new float[numTests];
    }

This is Literally all the code you need reference, this is not a bug its a syntax problem :)

You have allocated stuArray[count].stuScore with new[], but not stuArray[count].stuScore[j]. Only delete[] what you actually new[]. — Some programmer dude
– Some programmer dude, Commented May 8, 2018 at 3:27
You can't delete individual elements of an array you allocated with new. You can only delete the entire array. It's all or none. — drescherjm
– drescherjm, Commented May 8, 2018 at 3:30
is 'stuArray[i].stuScore = new float[numTests];' not doing just that? I assume this would create a new array of stuScores such that I can enter data in with a counter and delete with a counter? — Mike Remley
– Mike Remley, Commented May 8, 2018 at 3:31
@drescherjm So if I were to delete stuArray[count].stuScore that would be enough? It makes sense because I did the same with stuArray... ha — Mike Remley
– Mike Remley, Commented May 8, 2018 at 3:32
You can delete delete[] stuArray[count].stuScore but not delete[] stuArray[count].stuScore[j] — drescherjm
– drescherjm, Commented May 8, 2018 at 3:32

Kostas · Accepted Answer · 2018-05-08 03:40:19Z

1

Try delete[] stuArray[count].stuScore;

not delete[] stuArray[count].stuScore[j];

delete [] is made to delete an array allocated with new type[n]

You want to delete the pointer to the memory, not the actual memory.

edited May 8, 2018 at 3:40

answered May 8, 2018 at 3:36

Kostas

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Comments

Mike Remley · Accepted Answer · 2018-05-08 03:38:40Z

0

You can delete delete[] stuArray[count].stuScore but not delete[] stuArray[count].stuScore[j] - drescherjm

Fixed using:

do
{
    delete[] stuArray[count].stuScore;
    count++;
} while (count < numTests);

answered May 8, 2018 at 3:38

Mike Remley

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