Getting garbage printed

Question

I am trying the following simple CUDA C code but getting garbage value printed:

#include <stdio.h>

__global__ void hellocuda(int* tidx){
   *tidx = 100;
}

int main(){

    int* d_tidx;
    int* c;

    cudaMalloc((void**) &d_tidx, 1);

    c = (int*)malloc(sizeof(int));

    hellocuda<<<1,1>>>(d_tidx);

    cudaMemcpy(c, d_tidx, sizeof(int), cudaMemcpyDeviceToHost);

    printf("%d\n", *c);

    return EXIT_SUCCESS;
}

The output I am getting on this is: -273093020

Could someone help debugging this code. Thanks.

One problem i see is that your only allocating 1 byte but an int is 4 bytes. — Katianie, Dec 27 '13 at 18:04

alk · Accepted Answer · 2013-12-27T23:15:32.960

2

This line

printf("%d\n", *c);

pulls sizeof(*c) bytes from the stack, from which only the first byte is valid memory, as allocated by:

int * c;
...
c = (int*) malloc(1);

As sizeof(*c) definitly is larger then 1 the call to printf() above provokes undeinfed behaviuor.

Allthough I cannot really parse this:

cudaMalloc((void**) &d_tidx, 1);

The 1 looks obscure to me.

edited Dec 27 '13 at 23:15

answered Dec 27 '13 at 18:06

alk

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Thanks, I changed `cudaMalloc((void**) &d_tidx, 1);` to `cudaMalloc((void**) &d_tidx, sizeof(int));` and it worked. – Ketan Maheshwari Dec 27 '13 at 20:30

Getting garbage printed

1 Answers1