How to use mmap like malloc?

Question

I'm trying to allocate memory for 10x of my list struct then use it for my linked list but I keep getting a segmentation fault.

Valgrind

==3806== Invalid write of size 4
==3806==    at 0x4005FD: main (comp.c:14)
==3806==  Address 0xffffffffffffffff is not stack'd, malloc'd or (recently) free'd

Sample Code

#include <sys/mman.h>

typedef struct list {
    int num;
    struct list *next;
}list;

int main()
{
    list *nodes = mmap(NULL, sizeof(list) * 10, PROT_READ | PROT_WRITE, MAP_PRIVATE, -1, 0);

    nodes[0].num = 1;
    nodes[0].next = NULL;

}

Answer 1

The 0xffffffffffffffff almost surely means that mmap failed. If you want to use it to allocate memory like malloc , you have to do error checking just as you would for malloc , except that you need to test the returned value against MAP_FAILED instead of NULL .

The failure is probably because you are trying to map a nonexistent file descriptor -1 . This is only allowed when the MAP_ANONYMOUS flag is specified, which you did not include.