SIGSEGV on delete[] problem, recursive function calls

presencia

Hi everyone,
I have written a small program running fine until a Segmentation fault. Using a debugger I have localized the function the fault happens in. The Signal appears during a call to delete[] in the recursive function I have posted below. I have done some C coding before but I am fairly new to C++. I would really appreciate any help. I can't figure out where the problem is.

The function the SIGSEGV appears in is the following. It receives various pointers to arrays, compled is defined by "typedef complex<double> compled", the numbers m and i are powers of 2 and m/2 > i. I have inserted some output commands to track the problem.

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 int coeff2data_remaining (double * coeffs, int number_c, int next_c, compled * data, int m, int i, compled * primitive_root, int next_pp){

    //handle case of small number_c, no recursive call

    cout << "coeff2data_remaining (" <<coeffs<<","<<number_c<<", "<<next_c<<", "<<data<<", "<<m<<", "<<i<<", "<<primitive_root<<", "<<next_pp<<")"<<endl;

    if (number_c == 1){

        int index_data=0;

        for (int index_point = 1; index_point < m; ++index_point)

            if (index_point%i)

                data[index_data++]=*coeffs;

        return 0;

    }

    //group the coefficients in evens and odds, call this function recursively

    int half = m>>1;

    int number_evens = number_c>>1;

    int number_odds = (number_evens<<1 == number_c)? number_evens : number_evens+1;

    compled * data_evens = new compled [half-half/i];

    cout << "allocated data_evens: " <<data_evens<<", size: "<<(half-half/i)<<endl;

    compled * data_odds = new compled [half-half/i];

    cout << "allocated data_odds: " <<data_odds<<", size: "<<(half-half/i)<<endl;

    cout << "calling coeff2data_remaining twice ..."<<endl;

    coeff2data_remaining (coeffs, number_evens, next_c<<1, data_evens, m>>1, i, primitive_root, next_pp<<1);

    coeff2data_remaining (coeffs+next_c, number_odds, next_c<<1, data_odds, m>>1, i, primitive_root, next_pp<<1);
 
    //use each received data twice to calculate the desired data

    int index_data=0;

    int index_pp=next_pp;

    compled diff;

    for (int index_point = 1; index_point<half; ++index_point, index_pp+=next_pp)

        if (index_point%i){

            diff = primitive_root[index_pp]*data_odds[index_data];

            data[index_data]=data_evens[index_data]+diff;

            data[half+index_data]=data_evens[index_data]-diff;

            ++index_data;

        }
 
    //free allocated memory

    cout << "deleting data_evens: " <<data_evens<<endl;

    delete [] data_evens;

    cout << "deleting data_odds: " <<data_odds<<endl;

    delete [] data_odds;

    cout << "successful end of coeff2data_remaining (" <<coeffs<<","<<number_c<<", "<<next_c<<", "<<data<<", "<<m<<", "<<i<<", "<<primitive_root<<", "<<next_pp<<")"<<endl;

    return 0;

}

Running my program produces the following output. (The function is called twice from the outside before crashing.)

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 coeff2data_remaining (0x9ddc228,2, 1, 0x9ddc2f0, 4, 2, 0x9ddc008, 2)

allocated data_evens: 0x9ddc340, size: 1

allocated data_odds: 0x9ddc358, size: 1

calling coeff2data_remaining twice ...

coeff2data_remaining (0x9ddc228,1, 2, 0x9ddc340, 2, 2, 0x9ddc008, 4)

coeff2data_remaining (0x9ddc230,1, 2, 0x9ddc358, 2, 2, 0x9ddc008, 4)

deleting data_evens: 0x9ddc340

deleting data_odds: 0x9ddc358

successful end of coeff2data_remaining (0x9ddc228,2, 1, 0x9ddc2f0, 4, 2, 0x9ddc008, 2)

coeff2data_remaining (0x9ddc240,2, 1, 0x9ddc318, 4, 2, 0x9ddc008, 2)

allocated data_evens: 0x9ddc358, size: 1

allocated data_odds: 0x9ddc340, size: 1

calling coeff2data_remaining twice ...

coeff2data_remaining (0x9ddc240,1, 2, 0x9ddc358, 2, 2, 0x9ddc008, 4)

coeff2data_remaining (0x9ddc248,1, 2, 0x9ddc340, 2, 2, 0x9ddc008, 4)

deleting data_evens: 0x9ddc358

deleting data_odds: 0x9ddc340

As I said, any helpful comment is greatly appreciated. And I will be happy to privide any further information if needed.
~<><~~~~~ presencia

presencia

Hi everyone,
I believe to have found the error.
In line 31 it wrote

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data[half+index_data]=data_evens[index_data]-diff;

which was wrong, because I was writing "to the array" outside of its allocated bound. I probably overwrote some information needed for the delete of an array, therefore the program crashed processing the delete.
The line should have been

Expand|Select|Wrap|Line Numbers

data[half+index_data-half/i]=data_evens[index_data]-diff;

since before the call the data array had been allocated to have length (half*2)-(half*2)/i in line 15 or 17, respectively. Since the index_data will go to half-half/i - 1, everything should work out fine now.

Maybe I shoud have started all this using vectors with the at() function instead of raw arrays. I was just so used to arrays and didn't see much of a point there.
Thanks to everyone who has looked at this thread trying to help.
This thread can be closed.
~<><~~~~~ presencia

Banfa

Quote:

Originally Posted by presencia

Maybe I shoud have started all this using vectors with the at() function instead of raw arrays. I was just so used to arrays and didn't see much of a point there.

If you are using C++ then you should always use vectors instead of raw arrays. The overhead of using a vector is negligible, there can be a little overhead in creating the vector but a lot of that can be mitigated by using the vector correctly.

Hanging on to using arrays instead of vectors is indicative of someone semi-stuck in the C world but using C++, I know it took me ages to make the switch from defaulting to arrays to defaulting to vectors.

SIGSEGV on delete[] problem, recursive function calls

re: SIGSEGV on delete[] problem, recursive function calls

re: SIGSEGV on delete[] problem, recursive function calls

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