Memory Allocation Problems with structure - c++

Question

Why does the provided code crash at the following line?
data *fillA = (data*)calloc(matrixa->nzmax, sizeof(data));
#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <algorithm>
#include <time.h>
using namespace std;
struct csr
{
int rows;
int cols;
int nzmax;
int *rowPtr;
int *colInd;
double *values;
};
struct data
{
int entry;
int index;
};
bool descend(const data &a, const data &b)
{
return a.entry > b.entry;
}
static bool ascend(const data &a, const data &b)
{
return a.entry < b.entry;
}
void csrtranspose(struct csr *matrixa)
{
int i, j, counter;
double *tArray = NULL;
data *fillA = (data*)calloc(matrixa->nzmax, sizeof(data));//fails here
for (int i = 0; i < matrixa->nzmax; i++)
{
fillA[i].entry = matrixa->colInd[i];
fillA[i].index = i;
}
sort(fillA, fillA + matrixa->nzmax, ascend);
tArray = (double*)calloc(matrixa->nzmax, sizeof(double));
for (int i = 0; i < matrixa->nzmax; i++)
{
tArray[i] = matrixa->values[i];
}
for (int i = 0; i < matrixa->nzmax; i++)
{
matrixa->colInd[i] = fillA[i].entry;
matrixa->values[i] = tArray[fillA[i].index];
}
free(tArray);
free(fillA);
}
int main()
{
int i;
struct data *total = 0;
struct csr *s = 0;
int nrows = 6, ncols = 5, counter = 0, nzmax = 10, rows = 3, cols = 5;
double values[10] = {0.2135, 0.8648, 7, 0.3446, 0.1429, 6, 0.02311, 0.3599, 0.0866, 8 };
int rowPtr[4] = { 0, 3, 6, 10 };
int colInd[10] = { 0, 2, 4, 1, 2, 3, 0, 1, 2, 4 };
s = (struct csr*) calloc(1, sizeof(struct csr));
s->rows = rows;
s->cols = cols;
s->nzmax = nzmax;
s->rowPtr = (int*)calloc(s->rows + 1, sizeof(int));
s->colInd = (int*)calloc(s->nzmax, sizeof(int));
s->values = (double*)calloc(s->nzmax, sizeof(int));
for (i = 0; i<10; i++)
{
s->colInd[i] = colInd[i];
s->values[i] = values[i];
if (i <= s->rows)
{
s->rowPtr[i] = rowPtr[i];
}
}
csrtranspose(s);
getchar();
}

Answer 1

The reason why it crashes there is because memory has already been corrupted by previously faulty code. So, the problem is not there where it crashes, the problem is in code which executed earlier.
Specifically, this line:
s->values = (double*)calloc(s->nzmax, sizeof(int));
Allocates doubles, but uses sizeof(int), so it does not allocate enough memory.
EDIT
Recommendations:
As others have already pointed out, when working with C++, use the new operator instead of C-style memory allocation. It will save you from LOTS of problems.
If you insist on using C-style allocation, never use p = (type*)malloc( sizeof(type) ), always use p = (type*)malloc( sizeof( *p ) ). This will at least make it more evident when you make the very common mistake of allocating memory for the wrong type.

Answer 2

The line (double*)calloc(s->nzmax, sizeof(int)); in itself is a good reason to switch to C++ allocation, where it's impossible to make that mistake even if you copy-and-paste.
You're allocating too little memory and writing out of bounds.
Since all your sizes are known at compile time, you don't really need dynamic allocation at all.