C++ Second dynamic allocation while first works (same size)

Question

I used to work with 3D dynamic allocated arrays but I read that 1D array has better performance so I tried to transorm my 3D array in a 1D array.

I work with two big arrays (about 240*320*1000 double) and the allocation look like this :

int numberFiles; //about 1000, can change
int nRow; //240
int nCol; //320
double *inputData;
double *outputData;

inputData = (double*)malloc(nCol*nRow*numberFiles*sizeof(double)); //Always works
outputData = (double*)malloc(nCol*nRow*numberFiles*sizeof(double)); //Always fails

The second allocation always fail. Since the first doesn't, it's not a size problem. And since, when allocate this in a 3D arrays, it's also working, it's not a memory space problem

Any ideas why the second allocation fails ?

Thanks.

Chen Song.

PS : Sorry for the poor english.

PS2: Tried new Double[], same problems.

Edit : So allocation in a simple code works but as soon as I try to put it in my app, it's not working anymore. I'm woking with QtCreator with mingw32 and have matio(libraries to read MATLAB files) to read data. Here a code example of my program which give me error :

//Needed include
using namespace std;

int main(int argc, char ** argv)
{

    int k,i,j;
    double *matriceBrute,*matriceSortie;
    double* matData;
    const char * c;
    mat_t *matfp;
    matvar_t *matvar;

    QApplication app(argc,argv);
    // Getting the directory of the data and the files in it
    QString directoryPath = QFileDialog::getExistingDirectory();
    QDir myDir(directoryPath);
    myDir.setNameFilters(QStringList()<<"*.MAT");
    QStringList filesList = myDir.entryList(QDir::Files | QDir::Hidden);
    string fullPath= (directoryPath+"/"+filesList[0]).toLocal8Bit().constData();
    c = fullPath.c_str();
    // Loading the first one to get the size of the data
    matfp = Mat_Open(c,MAT_ACC_RDONLY);
    matvar = Mat_VarReadNextInfo(matfp);
    int read_err = Mat_VarReadDataAll(matfp,matvar);
    int numberFiles = (int)filesList.size();
    int nCol = matvar->dims[1];
    int nRow = matvar->dims[0];
    //Allocating
    matriceBrute = (double*)malloc(nCol*nRow*numberFiles*sizeof(double));

    matriceSortie = (double*)malloc(nCol*nRow*numberFiles*sizeof(double));
    //the first one works but not the second

    //loading the data in the allocated memory
    for (k=0;k<numberFiles;k++)
    {
        fullPath= (directoryPath+"/"+filesList[k]).toLocal8Bit().constData();
        c = fullPath.c_str();
        matfp = Mat_Open(c,MAT_ACC_RDONLY);
       matvar = Mat_VarReadNext(matfp);
        matData = (double*)(matvar->data);
        for (i=0;i<nRow;i++)
        {
            for (j=0;j<nCol;j++)
            {
                matriceBrute[i + nRow*(j+k*nCol)]=*(matData+(i+j*nRow));
                matriceSortie[i + nRow*(j+k*nCol)]=*(matData+(i+j*nRow));
            }

        }
        Mat_VarFree(matvar);
        Mat_Close(matfp);
    }
}

Answer 1

No error, it works.

#include <iostream>
using namespace std;

int main()
{
int numberFiles = 1000; //about 1000, can change
int nRow = 240; //240
int nCol = 240; //320
double *inputData;
double *outputData;

inputData = (double*)malloc(nCol*nRow*numberFiles*sizeof(double)); //Always works
outputData = (double*)malloc(nCol*nRow*numberFiles*sizeof(double)); //Always fails
if (inputData == NULL)
  cout << "inputData alloc failed" << endl;
  if (outputData == NULL)
  cout << "outputData alloc failed" << endl;
    return 0;
}

It does not print as failed, so, don't worry, be happy.

Answer 2

May it be memory fragmentation problem? If, for example, you can't alloc ~0.6Gb (by one heap) twice? First time you alloc it, at second - it just can't find in your physical memory such big heap of free memory? Which exception do you receive?