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cmallocosx-yosemitememset

Why I never see the Hello text in Console in this program?

This is the code I have, running on OS X Yosemite

int main(int argc, char *argv[]){
    while (1) {
        srand(time(NULL));
        int r = rand();
        printf("Allocating\n");
        int *pi = malloc(5000000 * sizeof(int));
        if(pi==NULL){
            printf("Hello");
        }
        memset(pi, r, 5000000 * sizeof(int));
    }
}

So this program eventually stops running, last lines in Console I see being:

Allocating

Allocating

Allocating

Killed: 9

Korays-MacBook-Pro:hello2 koraytugay$

If malloc does not return NULL in this situation, when will it do? My understanding is a memory allocation problem happens here, but why "Hello" is not printed?

Solution

  • Linux will kill the program if your memory requirement exceeds available memory making malloc never return NULL.

    You can turn this feature off using echo 2 > /proc/sys/vm/overcommit_memory.