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Full Discussion: Pointer addresses in multiples of 32 ?
Top Forums Programming Pointer addresses in multiples of 32 ? Post 302426354 by shamrock on Tuesday 1st of June 2010 03:39:30 PM
Old 06-01-2010
Quote:
Originally Posted by cyler
1. Why are the pointers' addresses every 32 ?
That depends on the bitness of your machine...if it is 32-bit then pointers will store 4 bytes and if it is 64-bit then pointers will store 8 bytes.
Quote:
Originally Posted by cyler
2. Am I correct in stating that memset is writing to memory that is not allocated to any of the 3 pointers ? Is it writing to memory in between the pointers ?
Depends on what memory locations a b and c are pointing to...just dont assume anything like that.
Quote:
Originally Posted by cyler
3. Are the 3 pointers contiguous in memory ?
Again dont assume anything...be satisfied with what the os gives you.
Quote:
Originally Posted by cyler
4. I only allocated 10 bytes for each pointer. So how can "a" be 73 chars long etc. ?
See the line in red below for the answer.
Code:
size_t bufsize = 10;

char *a = malloc(bufsize);
memset(a, 'a', bufsize - 1);
a[bufsize] = '\0';

char *b = malloc(bufsize);
memset(b, 'b', bufsize - 1);
b[bufsize] = '\0';

char *c = malloc(bufsize);
memset(c, 'c', bufsize - 1);
c[bufsize] = '\0';

size_t d = c - a;

memset(a, '-', d);
printf("a = %s => address: %i => number of chars: %i\n", a, a, strlen(a));
printf("b = %s => address: %i => number of chars: %i\n", b, b, strlen(b));
printf("c = %s => address: %i => number of chars: %i\n", c, c, strlen(c));
printf("d = %i\n", d);

 

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LEARN ABOUT MINIX

memset

MEMSET(3)                                                    Linux Programmer's Manual                                                   MEMSET(3)

NAME

       memset - fill memory with a constant byte

SYNOPSIS

       #include <string.h>

       void *memset(void *s, int c, size_t n);

DESCRIPTION

       The memset() function fills the first n bytes of the memory area pointed to by s with the constant byte c.

RETURN VALUE

       The memset() function returns a pointer to the memory area s.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       +----------+---------------+---------+
       |Interface | Attribute     | Value   |
       +----------+---------------+---------+
       |memset()  | Thread safety | MT-Safe |
       +----------+---------------+---------+
CONFORMING TO

       POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.

SEE ALSO

       bstring(3), bzero(3), swab(3), wmemset(3)

COLOPHON

       This  page is part of release 4.15 of the Linux man-pages project.  A description of the project, information about reporting bugs, and the
       latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.

GNU                                                                 2017-03-13                                                           MEMSET(3)
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