Re: malloc question

[ratheesh kannoth <ratheesh.ksz@xxxxxxxxx>]

On Tue, Apr 26, 2011 at 4:10 PM, Daniel Baluta <daniel.baluta@xxxxxxxxx> wrote:
> On Tue, Apr 26, 2011 at 1:33 PM, Randi Botse <nightdecoder@xxxxxxxxx> wrote:
>> Hi All,
>>
>> I want to ask malloc() behaviour, consider these codes;
>>
>> ...
>> char *ptr = malloc(1);
>> strcpy(ptr, "what");
>> puts(ptr);
>> ....
>>
>> Confusingly, the strcpy() copied all bytes to ptr, but I just manage
>> to allocate ptr only for 1 byte, I guess I will have segfault here,
>> why this happen? why the string successfully copied into ptr? , is
>> those code legal?
>
> You didn't get segfault because you were lucky.
>
> Memory is allocated in multiples of page size (usually 4K).
> The memory after your allocated byte is valid in your case.
>
> thanks,
> Daniel.
> --

U could read a little more about vm_page_struct. ( virtual address
space to  physical page ).  Try below code also for more
clarification.....

    char *ptr = malloc(1);
    strcpy(ptr, "what");
    free(ptr);
    strcpy(ptr, "hell");





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