Visit Our UNIX and Linux User Community


malloc function


 
Thread Tools Search this Thread
Top Forums Programming malloc function
# 8  
Old 09-30-2002
Quote:
Originally posted by rajashekaran
code:--------------------------------------------------------------------------------
p= (int*)malloc(sizeof(int)*580);
--------------------------------------------------------------------------------*/

/*my reply*/

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 declaration and
malloc function.
this is an basic question according to my knowledge.
please answer this. [/B]
The problem with the original code is that you are allocating that space for use by your program. You were only allocating a single address space and then advancing the pointer, potentially stepping on other programs and system processes.

By allocating the entire chunk you can freely increase the pointer within the chunk without having to worry about stepping on another processing and core'ing the machine.

Previous Thread | Next Thread
Test Your Knowledge in Computers #56
Difficulty: Easy
A flip-flop circuit stores 1 bit of data.
True or False?

10 More Discussions You Might Find Interesting

1. Programming

Malloc function returning NULL

Hi All, I am using malloc function for allocating dynamic memory. When I am using below code on Linux server its working fine, but When I am trying the same code on HP UNIX server its returning NULL. below is a fragment of code in which it is giving problem. tmp = (format_tree... (4 Replies)
Discussion started by: Taher Saifuddin
4 Replies

2. UNIX for Dummies Questions & Answers

Help with malloc()

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

3. Programming

malloc vs new speed

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

4. Programming

Regarding the maximum memory allocated by malloc() function on HP-UX B11.11

In a 'C' program,when I am trying to allocate memory with the help of malloc () function, it is allocating the memory up to a certain limit for e.g. in my case, it is 670 MB (approx). malloc() returns NULL if I allocate more than this amount of memory.When I tried to allocate memory in chunks of... (1 Reply)
Discussion started by: vipinsachan
1 Replies

5. UNIX for Advanced & Expert Users

Malloc Implementation in C

Hey Guys Some of my friends have got together and we are trying to write a basic kernel similar to Linux. I am trying to implement the malloc function in C and I am using a doubly linked list as the primary data structure. I need to allocate memory for this link list (duh...) and I don't feel... (2 Replies)
Discussion started by: rbansal2
2 Replies

6. Programming

Malloc implementation in C

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. Programming

malloc()

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

8. Programming

When to use Malloc?

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

9. Programming

malloc

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

10. Programming

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); (1 Reply)
Discussion started by: chenhao_no1
1 Replies
mapmalloc(3MALLOC)					Memory Allocation Library Functions					mapmalloc(3MALLOC)

NAME
mapmalloc - memory allocator SYNOPSIS
cc [ flag ... ] file ... -lmapmalloc [ library ... ] #include <stdlib.h> void *malloc(size_t size); void *calloc(size_t nelem, size_t elsize); void free(void * ptr); void *realloc(void *ptr, size_t size); DESCRIPTION
The collection of malloc functions in this library use mmap(2) instead of sbrk(2) for acquiring new heap space. The functions in this library are intended to be used only if necessary, when applications must call sbrk(), but need to call other library routines that might call malloc. The algorithms used by these functions are not sophisticated. There is no reclaiming of memory. The malloc() and free() functions provide a simple general-purpose memory allocation package. The malloc() function returns a pointer to a block of at least size bytes suitably aligned for any use. The argument to free() is a pointer to a block previously allocated by malloc(), calloc() or realloc(). If ptr is a NULL pointer, no action occurs. Undefined results will occur if the space assigned by malloc() is overrun or if some random number is handed to free(). The calloc() function allocates space for an array of nelem elements of size elsize. The space is initialized to zeros. The realloc() function changes the size of the block pointed to by ptr to size bytes and returns a pointer to the (possibly moved) block. The contents will be unchanged up to the lesser of the new and old sizes. If the new size of the block requires movement of the block, the space for the previous instantiation of the block is freed. If the new size is larger, the contents of the newly allocated portion of the block are unspecified. If ptr is NULL, realloc() behaves like malloc() for the specified size. If size is 0 and ptr is not a null pointer, the space pointed to is freed. Each of the allocation functions returns a pointer to space suitably aligned (after possible pointer coercion) for storage of any type of object. The malloc() and realloc() functions will fail if there is not enough available memory. Entry points for malloc_debug(), mallocmap(), mallopt(), mallinfo(), memalign(), and valloc() are empty routines, and are provided only to protect the user from mixing malloc() functions from different implementations. RETURN VALUES
If there is no available memory, malloc(), realloc(), and calloc() return a null pointer. When realloc() returns NULL, the block pointed to by ptr is left intact. If size, nelem, or elsize is 0, a unique pointer to the arena is returned. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |MT-Level |Safe | +-----------------------------+-----------------------------+ SEE ALSO
brk(2), getrlimit(2), mmap(2), realloc(3C), malloc(3MALLOC), attributes(5) SunOS 5.10 20 Feb 2004 mapmalloc(3MALLOC)

Featured Tech Videos