C - Rezervimi i memorjes me malloc dhe calloc

[3rror21]

Pershendetje te gjitheve!
Me qe ra fjala cuna se me eshte bere truri lemsh me (malloc-calloc) ,
spo e gjej as me nje vend qe ta sqaroje ashtu si duhet,
nqs se keni kohe me dhene nje pergj
faleminderit te gjitheve

[edspace]

Ketu ke nje faqe qe shpjegon perdorimin e memories ne C
http://www.gnu.org/software/libc/man...tion%20and%20C


Ketu ke faqen e MSDN per MALLOC
http://msdn.microsoft.com/library/de...crt_malloc.asp

Ketu ke faqen e MSDN per CALLOC
http://msdn.microsoft.com/library/de...crt_calloc.asp


C ka dy menyra per perdorimin e memories.
1. Statike - Perdoret per variablat globale dhe te pandryshueshme
2. Automatike - Perdoret per argumentat e funksioneve dhe variablat lokale qe krijohen dhe fshihen brenda territorit (scope) ku jane perdorur.

Ndonjehere kur je duke programuar nuk e di se sa memorie eshte e nevojshme prandaj te duhet te kerkosh memorien ne menyre Dinamike. Kjo behet duke thirur malloc( size_t x) ku x eshte nje numer i plote pozitiv qe cakton sa byte duhet te rezervoje malloc. Nqs kompjuteri gjen memorien e mjaftueshme, malloc do ktheje nje tregues (pointer) me adresen e rezerves. Nqs nuk ka memorie te mjaftueshme, malloc do ktheje NULL.

psh: Kemi krijuar nje strukture me emrin "postim" dhe sa here qe dikush poston dicka ne forum, programi duhet te gjeje memorien e nevojshme, para se ta hedhe postimin ne database.

struct postim{
   char titulli[50]; 
   char shkrimi[50];
   integer pergjigje;
   integer lexime;
}

// krijojme nje tregues (pointer) per strukturen "postim"
struct postim * p;

// llogarisim memorjen e nevojshme per nje postim
// dhe e kerkojme memorien me malloc
p = (struct postim *)malloc( sizeof(struct postim) );

if ( p == null ){
    printf("Nuk ka memorje te mjaftueshme per postimin");
}
else{
    printf("Postimi u hodh ne memorje" );

    hidh_ne_database(p);

    //lirojme memorien qe perdorem
    free(p);
    printf("\nMemorja u lirua"); 
}

calloc() eshte e ngjashme me malloc() por rezervon hapesiren e nevojshme per nje liste elementesh/objektesh pernjeheresh.
Psh:
p = (struct postim *)calloc(10, sizeof(struct postim) );

Rreshti me lart do rezervoje memorje per 10 postime.

[Clauss]

plus calloc e ben edhe initialise ( zero) space qe rezervon.
kur ngaterrohesh/sje i sigurt me free etc shiko edhe alloca.

[cunimartum]

Edi nuk i ke vajtur deri ne fund
Do ishte mire qe te silleshin problemet me te hasura me keto metoda, sepse problemet ne memory allocation po nuk i dite jane tragjike.

Ja nje shembull skandaloz
Bug klasik :

#include 
#include 
#include 
#include 
#include 
#include 

#define BLOCK_SIZE 65530

int recordlength = 0;
char format_string[10];

static int numcompare(const void *p1, const void *p2) {
	double i,j;
	sscanf(*(char **)p1,format_string,&i);
	sscanf(*(char **)p2,format_string,&j);

	if (i > j) return (1);
	if (i < j) return (-1);
	return(0);
	}

static int numrcompare(const void *p1, const void *p2) {
	double i,j;
	sscanf(*(char **)p1,format_string,&i);
	sscanf(*(char **)p2,format_string,&j);

	if (i < j) return (1);
	if (i > j) return (-1);
	return(0);
	}

static int strcompare(const void *p1, const void *p2) {
	return (strncmp(*(char **)p1,*(char **)p2,recordlength));
	}

static int strrcompare(const void *p1, const void *p2) {
	
	return (-1 * strncmp(*(char **)p1,*(char **)p2,recordlength));		
	}

static int stricompare(const void *p1, const void *p2) {
	return (strncasecmp(*(char **)p1,*(char **)p2,recordlength));
	}

static int strricompare(const void *p1, const void *p2) {
	return (-1 * strncasecmp(*(char **)p1,*(char **)p2,recordlength));
	}

void cleanup(char ***bl,int b,char ***rl) {
	int i;

	free(*rl);
	for (i = 0; i < b; i++)
		free(*bl[i]);		
	free(*bl);
	}

int main(int argc, char *argv[]) {
	int i;
	int fd;
	int maxrec;
	int read_bytes;
	int read_records;
	int blocks = 0;
	int records = 0;
	int numeric = 0;
	int reverse = 0;
	int ignorecase = 0;
	char **blocklist = NULL;
	char **recordlist = NULL;
	char *block;
	int (*compare)(const void *, const void *);

	/* handle arguments */
	if (argc < 3) {
		fprintf(stderr, "usage: sort   [options]");
		exit(1);
		}
	recordlength = strtol(argv[1],NULL,10);
	fd = open(argv[2],O_RDONLY);
	if (recordlength <= 0 || recordlength > BLOCK_SIZE || fd < 0)
		exit(1);
	if (argc >= 4) {			
		
		if (strchr(argv[3], 'r')) 
			reverse = 1;
		if (strchr(argv[3], 'n'))
			numeric = 1;
		if (strchr(argv[3], 'i'))
			ignorecase = 1;
		}
	if (numeric) {
		if (reverse) compare = numrcompare;		
		else compare = numcompare;
		}
	else if (ignorecase) {
		if (reverse) compare = strricompare;
		else compare = stricompare;
		}
	else {
		if (reverse) compare = strrcompare;
		else compare = strcompare;
		}
	sprintf(format_string,"%%%dlf",recordlength);

	
	do {
		block = (char *) malloc(BLOCK_SIZE);
		blocklist = (char **) realloc(blocklist, sizeof(char *) * (blocks + 1));
		if (block == NULL || blocklist == NULL)
			exit(1);
		blocklist[blocks++] = block;
		maxrec = BLOCK_SIZE / recordlength;	/* max # of records in block */
		read_bytes = read(fd,block,recordlength * maxrec);
		if (read_bytes <= 0)
			break;
		read_records = read_bytes / recordlength;	/* # records really read */
		recordlist = (char **) realloc(recordlist, sizeof(char *) *
												(records + read_records));
		if (recordlist == NULL)			
			exit(1);
		for (i = 0; i < read_records; i++)
			recordlist[records++] = block + recordlength * i;
		} while (read_bytes == recordlength * maxrec);
	close(fd);

    if (records) {					/* if there is something to do */
		/* now sort the data */
		qsort(recordlist,records,sizeof(char *),compare);

		/* output data to stdout */
		for (i = 0; i < records; i++)		
			write(1,recordlist[i],recordlength);
		}
	cleanup(&blocklist,blocks,&recordlist);
	exit(0);
	}

Programi simulon nje sort routine me tre opsione te mundshme -r ( per reverse se prapthi) -n(per numrat) dhe -i(per ignore case ) dhe nje mangesi "te vogel" duhet te kete rreshta te njejte ne filen qe do sortohet dhe duhet te dihet numri i karaktereve per rresht. ( Programi eshte pjese e nje skripti ne bash qe i rregullon thjeshte fare keto veti)

kompilimi ne Unix ose Linux:
cc -go mysort mysort.c
egzekutimi me file-in e dhene ( i pershtatshem per te nxjerre ne pah bugun) :
mysort 75 large.in

Normalisht duhet te kompilohet pa problem ne Windows, por nuk e di sa efikas do jete ambjenti aty per te gjetur bugun

behet renditja-sortimi i filit dhe ne fund hasim nje seg.Fault
Rast tipik qe DUHET ditur.


ps. dbx (ose-gdb) mysort core
bcheck -all mysort 75 large.in
mysort.errs created.

[cunimartum]

Ja dhe fili large.in