variable-sized array on stack

Asked Feb 02 '19 at 05:54

Active Feb 02 '19 at 09:23

Viewed 40 times

I'm trying to allocate a variable-sized array on stack. The program compiles with c99 option, but it generates segmentation fault. My debugger showed that no value can be assigned to the array im1.

int main()
{
    FILE * file = fopen("./image.jpg", "rb");

    fseek(file, 0, SEEK_END);
    const long len = ftell(file);
    uint8_t im1[len];
    for(int i=0;i<len;i++){
        im1[i] = 0;
    }

I'm programming on MacOS and use lldb for debugging. The image.jpg size is 14MB. The setting function with for loop does not work. Can someone please explain why it happens?

If possible, I want to allocate the array not on heap but on stack to maximize computing speed.

edited Feb 02 '19 at 09:23

asked Feb 02 '19 at 05:54

Nownuri

2

How long is that file? Note that your stask usually has a limited size and it's impossible to put too much there. – iBug Feb 02 '19 at 05:59
3

I don't think heap vs stack provides a noticeable difference in terms of computing speed - your worry is invalid. – iBug Feb 02 '19 at 06:01
"Can someone please explain why it happens?" ==? Post the value of `len`. – chux - Reinstate Monica Feb 02 '19 at 06:14
If the image is more than 8 MiB, it is too big. In fact, it needs to be noticeably less than 8 MiB. – Jonathan Leffler Feb 02 '19 at 06:15
stack allocation is orders of magnitudes faster than malloc, yes, but for large arrays would be insignificant when compared with the time it takes to process it. – Antti Haapala -- Слава Україні Feb 02 '19 at 06:34
Thank you all for your comments! The file size was 14MB. I didn't know that the stack size is limited like that. – Nownuri Feb 02 '19 at 09:22

variable-sized array on stack

0 Answers0