C++ Access Violation Error when setting value

Question

can someone explain to me why this code get's an access violation error when the last line runs but not when h_A[0] is set to 100?

int nx = 16384;
int ny = 16384;
int nxy = nx*ny;
int nBytes = nxy * sizeof(int);

int *h_A;
h_A = (int *) malloc(nBytes);
h_A[0] = 100;

int *h_B;
h_B = (int *) malloc(nBytes);
h_B[0] = 100;

The error is:

Unhandled exception at 0x01079554 in Test.exe: 0xC0000005: Access violation writing location 0x00000000.

Edit:

Here is the solution thanks to @owacoder

int nx = 1238;//8;
int ny = 16384;//6;
int nxy = nx*ny;
int nBytes = nxy * sizeof(int);


int *h_A;
if ((h_A = (int *) malloc(nBytes)) == NULL){
    printf("Malloc failed...\n");
    return 0;
} else {
    initialInt (h_A, nxy); // Fills matrix with numbers
}


int *h_B;
if ((h_B = (int *) malloc(nBytes)) == NULL){
    printf("Malloc failed...\n");
    return 0;
} else {
    initialInt (h_B, nxy); // Fills matrix with numbers
}

Any particular reason you feel the need to attempt to allocate about 1GB of memory at a time to then set a value that would fit in char or is this completely out of context? As mentioned your second malloc is likely failing ... if I had to guess it's because you're consuming more than the addressable space for a 32-bit process. — AJG85
@AJG85 it's for a class. We're supposed to use large numbers to test the difference between CUDA and CPU computations. — RayB

owacoder owacoder · Accepted Answer · 2015-10-07T22:25:42

The second allocation failed, while the first did not. (i.e. malloc returned NULL, out of memory) You should put error checking for an out of memory condition in your code.

C++ Access Violation Error when setting value

1 Answers