08-05-2002
a problem about malloc()
1 . Thanks everyone who read the post.
2 . the programe is that :
#include <stdio.h>
#include <string.h>
void do_it(char *p)
{
p = (char *) malloc(100);
(void )strcpy(p,"1234");
}
int main(void)
{
char *p;
do_it(p);
(void )printf("p = %s \n",p);
return 0;
}
cc -g a.c -o a.out
./a.out
it will show that "memory fault(coredump)"
3 . Why ? I think that malloc() get memory from heap , and the heap can be seen at everywhere in the programe .In other words , it is "global" .
4 Then I write another programe. it works correctly .
#include <stdio.h>
#include <string.h>
char *do_it(void)
{
return ((char *) malloc(100));
}
int main(void)
{
char *p;
p = do_it();
strcpy(p, "asdfa");
(void) printf("p = %s \n",p);
}
5 . Then , the point 4 declare that point 3 is correct , but it is not we want .
6 . Then I think the OS has changed the value p when do_it() function return
10 More Discussions You Might Find Interesting
1. Programming
hello sir
since by mentioning a integer pointer and storing the integers
by incrementing the pointer value
then what is the purpose of malloc?
u can decalre it as
in t *p;
several integers can be stored by incrementing the value of p,
hence what is the diffrence between this... (2 Replies)
Discussion started by: rajashekaran
2 Replies
2. Programming
Hello
This is a simple program i carried out in my machine
i dont know how it is working
#include<alloc.h>
#include<stdio.h>
mian()
{
int *p,j;
p= (int*)malloc(1);
for(j=1;j<=580;j++)
{
*p=j;
++p;
}
p=p-580;
for(j=1;j<=580;j++)
{
printf("%d",*p);
} (7 Replies)
Discussion started by: rajashekaran
7 Replies
3. Programming
Hi All!
Does some one know I am under UNIX system can not allocate more then 1 Mb memory? It broke program down.
Any information would be greatly appreciated.
Thanks. (2 Replies)
Discussion started by: prodigal
2 Replies
4. Programming
Hi!
I hope this is the correct forum to post the question even if I'm a newbie...
I am a C-newbie (and really on the edge to be a C-addict ;) ) and have a question.
When should I use malloc?
To state it differently, when should I NOT use malloc?
For instance, if I have an array of... (5 Replies)
Discussion started by: Tonje
5 Replies
5. Programming
Some one please explain me what is Dynamic memory allocation and the use of malloc() function.How do we allocate memory dynamically and also the other way? (3 Replies)
Discussion started by: rash123
3 Replies
6. Programming
Hey Guys
I am trying to implement the malloc function for my OS class and I am having a little trouble with it. I would be really grateful if I could get some hints on this problem.
So I am using a doubly-linked list as my data structure and I have to allocate memory for it (duh...). The... (1 Reply)
Discussion started by: Gambit_b
1 Replies
7. UNIX for Dummies Questions & Answers
Do kmalloc and malloc allocate from same heap ? (3 Replies)
Discussion started by: dragonpoint
3 Replies
8. Programming
Which one is faster among malloc and new?
My understanding is that since new also has to call constructors after allocating memory it must be slower than malloc.
Am I correct? (1 Reply)
Discussion started by: rupeshkp728
1 Replies
9. UNIX for Dummies Questions & Answers
Good day! I'm a newbie in C. I'm trying to get an unlimited input from the user using malloc then printing the inputs after the user presses enter. My code works, but there's a warning that I don't know how to fix. Please help me. Thank you.
Here's my code:
#include <stdio.h>
#include... (6 Replies)
Discussion started by: eracav
6 Replies
10. Programming
Hello,
I am trying to read a text file into linked list, but always got the first and last records wrong.
1) The problem looks related to the initialization of the node temp with malloc(), but could not figure it out. No error/warning at compiling, though.
2) The output file is empty,... (10 Replies)
Discussion started by: yifangt
10 Replies
LEARN ABOUT OSX
malloc_zone_memalign
MALLOC_ZONE_MALLOC(3) BSD Library Functions Manual MALLOC_ZONE_MALLOC(3)
NAME
malloc_create_zone, malloc_destroy_zone, malloc_default_zone, malloc_zone_from_ptr, malloc_zone_malloc, malloc_zone_calloc,
malloc_zone_valloc, malloc_zone_realloc, malloc_zone_memalign, malloc_zone_free -- zone-based memory allocation
SYNOPSIS
#include <malloc/malloc.h>
malloc_zone_t *
malloc_create_zone(vm_size_t start_size, unsigned flags);
void
malloc_destroy_zone(malloc_zone_t *zone);
malloc_zone_t *
malloc_default_zone(void);
malloc_zone_t *
malloc_zone_from_ptr(const void *ptr);
void *
malloc_zone_malloc(malloc_zone_t *zone, size_t size);
void *
malloc_zone_calloc(malloc_zone_t *zone, size_t num_items, size_t size);
void *
malloc_zone_valloc(malloc_zone_t *zone, size_t size);
void *
malloc_zone_realloc(malloc_zone_t *zone, void *ptr, size_t size);
void *
malloc_zone_memalign(malloc_zone_t *zone, size_t alignment, size_t size);
void
malloc_zone_free(malloc_zone_t *zone, void *ptr);
DESCRIPTION
The malloc_create_zone() function creates a malloc zone, advising an initial allocation of start_size bytes, and specifying flags that alter
the standard behavior of the zone. The returned malloc zone can be used to provide custom allocation and deallocation behavior, and to
retrieve additional information about the allocations in that zone.
The malloc_destroy_zone() function deallocates all memory associated with objects in zone as well as zone itself.
The malloc_default_zone() function returns the default system malloc zone, used by malloc(3), and free(3).
The malloc_zone_from_ptr() function returns a pointer to the malloc zone which contains ptr or NULL, if the pointer does not point to an
allocated object in any current malloc zone.
The malloc_zone_malloc(), malloc_zone_calloc(), malloc_zone_valloc(), malloc_zone_realloc(), malloc_zone_memalign(), and malloc_zone_free()
perform the same task on zone as their non-prefixed variants, malloc(3), calloc(3), valloc(3), realloc(3), posix_memalign(3), and free(3)
perform on the default system malloc zone.
RETURN VALUES
The malloc_create_zone(), malloc_default_zone(), and malloc_zone_from_ptr() functions return a pointer to a malloc_zone_t structure, or NULL
if there was an error.
The malloc_zone_malloc(), malloc_zone_calloc(), malloc_zone_valloc(), malloc_zone_realloc(), and malloc_zone_memalign() functions return a
pointer to allocated memory. If there is an error, they return a NULL pointer. They are not required to set errno.
SEE ALSO
malloc(3), posix_memalign(3)
BSD
Aug 13, 2008 BSD