_C CUSTOMIZED MEMORY ALLOCATORS_ by Paul Anderson
[LISTING ONE]
/* sym1.c - symbol table data types */
#include <stdio.h> #include "xalloc.h" #include "defs.h"
main() {
Symbol *p1, *p2; char *ps = "test string"; int *p5;
p1 = (Symbol *) xmalloc(sizeof(struct Symbol)); p1->dtype = STRING; p1->val.pstring = xmalloc(strlen(ps) + 1); strcpy(p1->val.pstring, ps);
p2 = (Symbol *) xmalloc(sizeof(struct Symbol)); p2->dtype = DOUBLE; p2->val.pdouble = (double *) xmalloc(sizeof(double)); *p2->val.pdouble = 6.7e-13;
printf("%s\n", p1->val.pstring);
printf("%g\n", *p2->val.pdouble);
p5 = (int *) xmalloc(30000 * sizeof(int));
}
$ sym1 test string 6.7e-13 file sym1.c - line 26: malloc error for 60000 bytes
[LISTING TWO]
#include <stdio.h> #include <malloc.h>
#define MAXBUF 256 /* size of debug buffer */ static char *dbuf[MAXBUF]; /* debug buffer */
/* ymalloc2.c - front end for malloc()
Version 2
*/
char *ymalloc(file, lineno, nbytes) char *file; int lineno; unsigned int nbytes; {
char *pheap; void install();
pheap = malloc(nbytes);
if (pheap == (char *) NULL) {
fprintf(stderr,"file %s - line %d: malloc error for %u bytes\n",
file, lineno, nbytes);
exit(1);
}
install(pheap); /* place in debug buffer */
return pheap;
}
void install(pheap) /* store heap pointer in debug buffer */ char *pheap; {
register char **pbuf;
for (pbuf = dbuf; pbuf < dbuf + MAXBUF; pbuf++)
if (*pbuf == (char *) NULL) {
*pbuf = pheap;
return;
}
fprintf(stderr, "No room left in debug buffer\n");
exit(1);
}
char *yrealloc(file, lineno, oldp, nbytes) char *file, *oldp; int lineno; unsigned int nbytes; {
char *newp; register char **pbuf; short found = 0;
if (oldp != (char *) NULL)
for (pbuf = dbuf; pbuf < dbuf + MAXBUF; pbuf++)
if (*pbuf == oldp) { /* find oldp's slot */
found = 1;
break;
}
if (!found) {
fprintf(stderr,"file %s - line %d: realloc error for address %x\n",
file, lineno, oldp);
exit(1);
}
newp = realloc(oldp, nbytes);
if (newp == (char *) NULL) {
fprintf(stderr,"file %s - line %d: realloc error for %u bytes\n",
file, lineno, nbytes);
exit(1);
}
*pbuf = newp; /* replace in debug buffer's old slot */
return newp;
}
void yfree(file, lineno, pheap) char *file, *pheap; int lineno; {
register char **pbuf;
if (pheap != (char *) NULL)
for (pbuf = dbuf; pbuf < dbuf + MAXBUF; pbuf++)
if (*pbuf == pheap) {
*pbuf = NULL;
free(pheap);
return;
}
fprintf(stderr,"file %s - line %d: free error for address %x\n",
file, lineno, pheap);
exit(1);
}
[LISTING THREE]
/* sym2.c - more symbol table data types */
#include <stdio.h> #include "xalloc.h" #include "defs.h"
main() {
Symbol *p1, *p2; char *ps = "test string"; char *ps2 = "much longer test string";
p1 = (Symbol *) xmalloc(sizeof(struct Symbol)); p1->dtype = STRING; p1->val.pstring = xmalloc(strlen(ps) + 1); strcpy(p1->val.pstring, ps);
p2 = (Symbol *) xmalloc(sizeof(struct Symbol)); p2->dtype = DOUBLE; p2->val.pdouble = (double *) xmalloc(sizeof(double)); *p2->val.pdouble = 6.7e-13;
printf("%s\n", p1->val.pstring);
printf("%g\n", *p2->val.pdouble);
p1->val.pstring = xrealloc(p1->val.pstring, strlen(ps2) + 1);
strcpy(p1->val.pstring, ps2);
printf("%s\n", p1->val.pstring);
xfree((char *) p2->val.pdouble); xfree(ps2); /* free a bad pointer */
}
$ sym2 test string 6.7e-13 much longer test string file sym2.c - line 31: free error for address 2634
Example 1: Out of bounds references
/* twzone.c - array out of bounds */
main() {
int buf[10];
buf[-4] = 1; /* negative subscript */ buf[10] = 2; /* one step beyond */
printf("%d %d\n", *(buf - 4), *(buf + 10));
}
Example 2: Program that demonstartes xcalloc()
/* neg.c - negative subscripts with xcalloc */
#include <stdio.h>
main() {
char *xcalloc(); int *p, *q;
p = (int *) xcalloc(10, sizeof(int)); q = (int *) xcalloc(15, sizeof(int));
fill(p); /* fill with 10 numbers */ display(p); /* print 10 numbers */
fill(q); /* fill with 15 numbers */ display(q); /* print 15 numbers */
}
$ neg
1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Example 3: xcalloc() routine
#include <stdio.h> #include <malloc.h> #include <memory.h>
char *xcalloc(nitems, size) /* custom calloc() */ unsigned nitems, size; {
char *pheap; unsigned blksize;
blksize = nitems * size; /* size of chunk */
if ((pheap = malloc(blksize + sizeof(int))) == NULL) {
fprintf(stderr, "Can't malloc on heap\n");
exit(1);
}
*(int *)pheap = nitems; /* store no. of items in heap */
memset(pheap + sizeof(int), 0, blksize); /* zero the area */
return pheap + sizeof(int); /* pointer to data */
}