Double free or corruption (!prev) error in my c++ destructor

Question

I have a program that does operations on a vector, not altering them but just reading once and then writing out what is required based on what is given. My program runs but I get this error at the end;

*** Error in './volimage: double free or corruption (!prev): 0x00000000123c10 ***

I have googled, and it seems the problem is with my destructor, but I can't for the life of me find or solve it.

This is the destructor:

VolImage::~VolImage()
{
    std::cout << "Destructor" << std::endl;
    //deconstructing the vector of slices
    int i, j, k;
    for (i = 0; i<size; i++)
    {
        for (j = 0; j<height; j++)
        {
            delete[] slices[i][j];
        }
        delete[] slices[i]; 
    }
    slices.clear();
}

The vector was populated using the following:

std::vector<unsigned char**> slices; // data for each slice, in order

//populating vector
int i, j, k;
unsigned char ** rows = new unsigned char*[height];
for (i = 0; i < size; i++) 
{
    for (j = 0; j < height; j++) 
    {
        unsigned char* cols = new unsigned char[width];
        string num = "%d" + j;
        fileName = baseName + num + ".raw";
        myFile.open(fileName);
        for (k = 0; k < width; k++)
        {
            unsigned char x;
            myFile >> x;
            cols[k] = x;
        }
        myFile.close();
        rows[i] = cols;
    }
    slices.push_back(rows);
}

Thanks, a hasty reply would be appreciated as i need to submit this soon

Shouldn't it be `rows[j] = cols;` instead of `rows[i] = cols;`? I.e. `j`, not `i`? — Sergey Kalinichenko, Mar 24 '16 at 00:15
Didn't see that, thanks, but i still get the destruction problem — Thusoluminati Al-Zawahiri Khar, Mar 24 '16 at 00:44

score 2 · Accepted Answer · answered Mar 24 '16 at 01:09

You allocated the buffer for storing pointers to pointers only once. You have to allocate ones for each rows.

Also note that the line string num = "%d" + j; has a big chance to cause out-of-range access because "%d" + j is equivalent to &"%d"[j] and only 0 <= j < 3 is allowed.

One more thing: rows[i] = cols; should be rows[j] = cols; as @dasblinkenlight says.

Try this:

//populating vector
int i, j, k;
for (i = 0; i < size; i++) 
{
    unsigned char ** rows = new unsigned char*[height]; // move this line
    for (j = 0; j < height; j++) 
    {
        unsigned char* cols = new unsigned char[width];
        std::stringstream ss;
        string num;
        ss << j;
        ss >> num; // convert the integer stored in j to string
        fileName = baseName + num + ".raw";
        myFile.open(fileName);
        for (k = 0; k < width; k++)
        {
            unsigned char x;
            myFile >> x;
            cols[k] = x;
        }
        myFile.close();
        rows[j] = cols;
    }
    slices.push_back(rows);
}

Add #include <sstream> to your code if it doesn't exists to use std::stringstream.

Thank you very much, it works now. On a side note, if i wanted to count the bytes required to store the data how would i go about that? sizeOf(slices) seems to just return 24 — Thusoluminati Al-Zawahiri Khar, Mar 24 '16 at 01:30

score -1 · Answer 2 · edited May 23 '17 at 11:45

-1

This is not a direct answer, I agree with @MikeCAT's answer. I want to add to the comment posted under the soln : (I dont have enough rep to post a comment directly). Please see here for why sizeof(slices) returns 24.

How about something like : (width * height * sizeof(slices[0][0][0]) ) * size, provided that slices[0][0][0] exists.

edited May 23 '17 at 11:45

Community

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answered Mar 24 '16 at 02:09

user3554704

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That's what i ended up doing, the problem is the pointers, the pointers must be included too – Thusoluminati Al-Zawahiri Khar Mar 24 '16 at 02:28
Please correct me, I might not understand this : If you have (height * cols_ptr_size) + (size * rows_ptr_size) that should give you the sum size of the pointers? Pointers should usually have fixed sizes (32-bit or 64-bit, depending on the architecture and I'm assuming standard examples not <32 such as 16-bit). Sorry if I'm not of more help. – user3554704 Mar 24 '16 at 02:51
Thanks :) very helpful – Thusoluminati Al-Zawahiri Khar Mar 24 '16 at 03:13

Double free or corruption (!prev) error in my c++ destructor

2 Answers2