stubborn

C programmer, Linux kernel, know how to program, know how to _learn_

know hardware, basic electronic

attractive salary (later on, ask my HRD manager)

Willing to work in Jakarta, Indonesia

send me an email : dsasongko + _at_ + mobiztech.com

this is very funny and interesting :

write this code :

main()
{
    int *p1 = malloc(sizeof(int));
    *p1 = 3;
    printf("%d, %p\n", *p1, p1);
    free(p1);
    printf("%d, %p\n", *p1, p1);
}

i expect that in the second printf, i will get Segmentation fault. I assumed that when the pointer p1 is free‘d it will be NULL, destroyed. In fact, the memory still exist but the content is null.

ruckuus@ruckuux:~/Code$ ./p
3 0x804a008
0 0x804a008

A little thing that leads me to here :

MALLOC(3)                    Linux Programmer’s Manual                           MALLOC(3)

NAME

       calloc, malloc, free, realloc - Allocate and free dynamic memory

SYNOPSIS

       #include <stdlib.h>

       void *calloc(size_t nmemb, size_t size);

       void *malloc(size_t size);

       void free(void *ptr);

       void *realloc(void *ptr, size_t size);

see, void free (void *ptr) ? what does it mean ?

free()  frees the memory space pointed to by ptr, which must have been returned by
a previous call to malloc(), calloc() or realloc(). Otherwise, or if free(ptr) has
already been called before, undefined behavior occurs. If ptr is NULL, no operation
is performed.

free will never delete / free “memory space” pointed by ptr. but yes it will delete it’s content. Did i miss something here ?

this will be different if the code look like this :

main()
{
    int *p1 = malloc(sizeof(int));
    *p1 = 3;
    printf("%d, %p\n", *p1, p1);
    free(p1);
    p1 = 0;
    printf("%d, %p\n", *p1, p1);
}

Correctly this is forbidden, accessing NULL :

ruckuus@ruckuux:~/Code$ ./p
3 0x804a008
Segmentation fault

This might be a reminder, if i’m _not_wrong_, very long time ago with the first code i got Seg fault because as i remember free will destroy the pointer and it’s memory space is unusable anymore. So, is this a reminder that i might have been wrong for very long time in case of free pointer ?

Q : If you understood that jealousy is not good for your health, why do you still feel that kind of shit ?

A : it happens, always like that

Q : why ?

A : you ask wrong question, it supposed to be “what ?”

1. it’s confusing
2. it raises assumption, and it’s bad
3. it wastes your time and your reader’s time

This might be …

the end of our trip, mission accomplished. Mission to bring a new you, not totally new, and actually nothing. You have already had those miracles, but somehow they have never shown before. Born incomplete, and now you’re completed.

I’m glad to know that.