Malloc in C why to use it

Question

I am new at C language and I need to create a queue and I don´t if I need to use a malloc (memory allocation) and how to use it. I had run add, remove, size and isempty without malloc and it worked.

    void e1_init(e1queue_t* q){
    q->head = 0;
    q->tail = sizeof(q->queue)/sizeof(int)-1;
    q->size=0;  
    }

Thanks.

score 1 · Answer 1 · edited May 23 '17 at 11:48

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In C, there are two kinds of memory:

The Stack
The Heap

Stack memory is rather limited and is used for automatic variables in functions, processing overhead, things like that.

When you need a larger chunk of memory, you need to get it from the heap.

Not an exact duplicate of this answer, but this seems to be a good description:

What and where are the stack and heap?

edited May 23 '17 at 11:48

Community

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answered Oct 20 '12 at 07:13

Jeremy J Starcher

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the C standard doesn't use terms like 'stack' or 'heap' – user411313 Oct 20 '12 at 08:06
1

@user411313 -- Agreed, nor does the C standard say a byte is 8 bits long. Some things are just so common, however, they *almost* be taken for granted. On systems that don't actually have a stack, the stack can be emulated. (VM/CMS) – Jeremy J Starcher Oct 20 '12 at 08:32

score 0 · Answer 2 · answered Oct 20 '12 at 07:09

C dynamic memory allocation refers to performing dynamic memory allocation in the C programming language via a group of functions in the C standard library, namely malloc, realloc, calloc and free

Syntax:

#include <stdlib.h>

Description:

The function malloc() returns a pointer to a chunk of memory of size size, or NULL if there is an error. The memory pointed to will be on the heap, not the stack, so make sure to free it when you are done with it.

Example:

typedef struct data_type {
  int age;
  char name[20];
} data;

data *bob;
bob = (data*) malloc( sizeof(data) );
if( bob != NULL ) {
  bob->age = 22;
  strcpy( bob->name, "Robert" );
  printf( "%s is %d years old\n", bob->name, bob->age );
}
free( bob );

Good Read C dynamic memory allocation

And I use malloc in e1_init and where I will use free? Thanks — tomss, Oct 20 '12 at 07:18

score 0 · Answer 3 · answered Oct 20 '12 at 07:24

There are many reasons to use malloc() function.

malloc() is used to dynamically allocate memory for variables. why? There can be many reasons to allocate memory dynamically. For instance if the size of a certain object/variable isn't known at COMPILE time, and there might be a reason to increase it later on, then its required to increase the memory requirement. and this is where malloc comes in.
malloc() is used to initialize POINTERS why? POINTERS that aren't initialized point to a random location. This location may be in-accessible and might crash the program. When malloc is used, it increases the heap storage and points the randomly initialized pointer to a "sane" location, which can be read/written to.
also, pointers initialized with malloc can be resized using realloc() method. This makes memory management flexible(and error prone as well)

at e1_end() which should be called before exiting the program to de-initialize(or free) all the nodes in your queue. Note it will need to be called in a loop to free all the nodes. — Aniket Inge, Oct 20 '12 at 07:34
So I just have to use free to remove the entire queue? If I have a malloc I will have to use a free? — tomss, Oct 20 '12 at 07:45

Malloc in C why to use it

3 Answers3