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Full Discussion: Memory allocation in C
Top Forums Programming Memory allocation in C Post 302438057 by unx_freak on Sunday 18th of July 2010 05:14:07 AM
Old 07-18-2010
Memory allocation in C

Hi Experts
I need some help in static memory allocation in C. I have a program in which I declared 2 variables, one char array and one integer. I was little surprised to see the addresses of the variables.

First:

Code:
int x;
char a[2];
printf("%u %u\n', &x, a);

I got the addresses displayed as : 3219437172 3219437170
The above result is straight forward wherein the array a got 2 bytes allocated.

Second:

When I changed the program as below:
Code:
int x;
char a[3];
printf("%u %u\n', &x, a);

I got the addresses displayed as : 3219437172 3219437144
The array a got allocated 28 bytes when the declaration is for 3 bytes.

Why so?
 

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array(3)						     Library Functions Manual							  array(3)

NAME
array - The array library interface SYNTAX
#include <array.h> DESCRIPTION
An allocated array variable keeps track of o a (nonzero) pointer to a dynamically allocated region of memory; o the number of bytes allocated (always positive); and o the number of bytes initialized (between 0 and the number of bytes allocated). There are two other possibilities for the state of an array variable: unallocated and failed. In both cases, there is no dynamically allo- cated region of memory. A new array variable is normally created as a static variable: #include "array.h" static array x; At this point it is unallocated. The array library provides various allocation and inspection functions. A new array variable can also be created dynamically. It must be initialized to all-0, meaning unallocated, before it is given to any of the array functions. It must be returned to the unallocated (or failed) state, for example with array_reset, before it is destroyed. These rules prevent all memory leaks. Expansion and inspection array x; t* p1 = array_allocate(&x,sizeof(t),pos); t* p2 = array_get(&x,sizeof(t),pos); t* p3 = array_start(&x); int64 len = array_length(&x,sizeof(t)); int64 bytes = array_bytes(&x); Truncation and deallocation array x; array_truncate(&x,sizeof(t),len); array_trunc(&x); array_reset(&x); array_fail(&x); Comparison array x; array y; if (array_equal(&x,&y)) /* arrays are equal... */ Concatenation array x; array y; array_cat(&x,&y); array_catb(&x,"fnord",5); array_cats(&x,"fnord"); array_cats0(&x,"fnord"); /* also append the */ array_cat0(&x); /* append */ array_cate(&x,"fnord",1,4); /* append "nor" */ ORIGINAL API DEFINITION
http://cr.yp.to/lib/array.html SEE ALSO
array_get(3), array_start(3), array_fail(3) array(3)
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