realloc

[Roy]

Hi all :
My code below :

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

char *cat(char *s, const char *t)
{
char *tmp;

if (s == NULL)
tmp = realloc(s,strle n(t) + 1);
else
tmp = realloc(s,strle n(s) + strlen(t) + 1);
if (tmp == NULL) {
fputs("realloc error",stderr);
exit(1);
}
while (*tmp++); // search for '\0' and stop
tmp--; //the position of '\0'
while (*tmp++ = *t++) ;
s = tmp;
return s;
}

int main()
{
char *tmp;
char *s;

s = NULL;
tmp = cat(s,"oh");
printf("%s\n",t mp);
tmp = cat(s,"haha");
printf("%s\n",t mp);
return 0;
}
my problem is when I run the program the reslut is some blanks. I just
wrote a small routine like strcat and check the realloc and tmp pointer
carefully but found nothing.

[baumann]

Roy wrote:

Hi all :
My code below :

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

char *cat(char *s, const char *t)
{
char *tmp;

if (s == NULL)
tmp = realloc(s,strle n(t) + 1);
else
tmp = realloc(s,strle n(s) + strlen(t) + 1);
if (tmp == NULL) {
fputs("realloc error",stderr);
exit(1);
}
while (*tmp++); // search for '\0' and stop
the above statement is not right, when s = null, what do you expect the
*tmp is?
tmp--; //the position of '\0'
while (*tmp++ = *t++) ;
s = tmp;
return s;
}

int main()
{
char *tmp;
char *s;

s = NULL;
tmp = cat(s,"oh");
printf("%s\n",t mp);
tmp = cat(s,"haha");
printf("%s\n",t mp);
return 0;
}
my problem is when I run the program the reslut is some blanks. I just wrote a small routine like strcat and check the realloc and tmp pointer carefully but found nothing.

[Roy]

baumann@pan wrote:

Roy wrote:

Hi all :
My code below :

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

char *cat(char *s, const char *t)
{
char *tmp;
correct here:
if (s == NULL) {
tmp = realloc(s,strle n(t) + 1);
while(*tmp++ = *t++); // copy *t to *tmp.
} else { tmp = realloc(s,strle n(s) + strlen(t) + 1);
if (tmp == NULL) {
fputs("realloc error",stderr);
exit(1);
}
while (*tmp++); // search for '\0' and stop

the above statement is not right, when s = null, what do you expect
the
*tmp is?
Now handled the s=null but still blanks...

tmp--; //the position of '\0'
while (*tmp++ = *t++) ;
}

s = tmp;
return s;

}

int main()
{
char *tmp;
char *s;

s = NULL;
tmp = cat(s,"oh");
printf("%s\n",t mp);
tmp = cat(s,"haha");
printf("%s\n",t mp);
return 0;
}
my problem is when I run the program the reslut is some blanks. I

just

wrote a small routine like strcat and check the realloc and tmp

pointer

carefully but found nothing.

[pete]

Roy wrote:

Hi all :
My code below :

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

char *cat(char *s, const char *t)
{
char *tmp;

if (s == NULL)
tmp = realloc(s,strle n(t) + 1);
else
tmp = realloc(s,strle n(s) + strlen(t) + 1);
if (tmp == NULL) {
fputs("realloc error",stderr);
exit(1);
}
while (*tmp++); // search for '\0' and stop
tmp--; //the position of '\0'
while (*tmp++ = *t++) ;
s = tmp;
return s;
}

int main()
{
char *tmp;
char *s;

s = NULL;
tmp = cat(s,"oh");
printf("%s\n",t mp);
tmp = cat(s,"haha");
printf("%s\n",t mp);
return 0;
}

char *cat(char *s, const char *t)
{
char *tmp;

if (s == NULL) {
tmp = realloc(s, strlen(t) + 1);
*tmp = '\0';
} else {
tmp = realloc(s, strlen(s) + strlen(t) + 1);
}
if (tmp == NULL) {
fputs("realloc error",stderr);
exit(EXIT_FAILU RE);
}
s = tmp;
while (*tmp++ != '\0') {
;
}
tmp--;
while ((*tmp++ = *t++) != '\0') {
;
}
return s;
}

--
pete

[Al Bowers]

pete wrote:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main()
{
char *tmp;
char *s;

s = NULL;
tmp = cat(s,"oh");
printf("%s\n",t mp);
tmp = cat(s,"haha");
printf("%s\n",t mp);
return 0;
}

char *cat(char *s, const char *t)
{
char *tmp;

if (s == NULL) {
tmp = realloc(s, strlen(t) + 1);
*tmp = '\0';

Here is a slight flaw. You do not want to assign to *tmp
BEFORE you have checked tmp value for a possible NULL.
} else {
tmp = realloc(s, strlen(s) + strlen(t) + 1);
}
if (tmp == NULL) {
fputs("realloc error",stderr);
exit(EXIT_FAILU RE);
}
s = tmp;
while (*tmp++ != '\0') {
;
}
tmp--;
while ((*tmp++ = *t++) != '\0') {
;
}
return s;
}

This definition will abort the program if dynamic allocation
fails. Another less virulent act on the executable would be
give a signal to the caller, via the return value, or some
other means, that the function was not successful in the
operation.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int cat(char **s1, const char *s2);

int main(void)
{
char *s = NULL;

if(cat(&s,"Hell o"))
{
if(cat(&s," and Goodbye"))
printf("s = \"%s\"\n",s) ;
else puts("Memory allocation failure");
}
else puts("Memory allocation failure");
free(s);
return 0;
}

int cat(char **s1, const char *s2)
{
int ret = 0; /* value would indicate failure */

if(s1 && s2)
{
char *tmp;
size_t sz = *s1?strlen(*s1) +strlen(s2)+1:s trlen(s2)+1;
if((tmp = realloc(*s1,sz) ) != NULL)
{
if(!*s1) *tmp = '\0';
strcat(tmp,s2);
*s1 = tmp;
ret = 1; /* value would indicate success */
}
}
return ret;
}

--
Al Bowers
Tampa, Fl USA
mailto: xa******@myrapi dsys.com (remove the x to send email)
http://www.geocities.com/abowers822/

[pete]

Al Bowers wrote:

pete wrote:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main()
{
char *tmp;
char *s;

s = NULL;
tmp = cat(s,"oh");
printf("%s\n",t mp);
tmp = cat(s,"haha");
Probably would be a better demonstration with
tmp = cat(tmp, "haha");
printf("%s\n",t mp);
return 0;
}

char *cat(char *s, const char *t)
{
char *tmp;

if (s == NULL) {
tmp = realloc(s, strlen(t) + 1);
*tmp = '\0';

Here is a slight flaw. You do not want to assign to *tmp
BEFORE you have checked tmp value for a possible NULL.

Thank you.

if (tmp == NULL) {
fputs("realloc error",stderr);
exit(EXIT_FAILU RE);
}

This definition will abort the program if dynamic allocation
fails. Another less virulent act on the executable would be
give a signal to the caller, via the return value, or some
other means, that the function was not successful in the
operation.

/* I'm taking another shot. */

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

char *cat(char *s, const char *t);

int main(void)
{
char *s;

s = cat(NULL, "oh");
if (s != NULL) {
printf("%s\n", s);
}
s = cat(s, "haha");
if (s != NULL) {
printf("%s\n", s);
}
return 0;
}

char *cat(char *s, const char *t)
{
char *tmp;

if (s == NULL) {
tmp = calloc(1, strlen(t) + 1);
} else {
tmp = realloc(s, strlen(s) + strlen(t) + 1);
}
s = tmp;
if (tmp != NULL) {
while (*tmp++ != '\0') {
;
}
tmp--;
while ((*tmp++ = *t++) != '\0') {
;
}
}
return s;
}

--
pete

[pete]

pete wrote:

Al Bowers wrote:

pete wrote:

/* I'm taking another shot. */

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

char *cat(char *s, const char *t);

int main(void)
{
char *s;

s = cat(NULL, "oh");
if (s != NULL) {
printf("%s\n", s);
}
s = cat(s, "haha");
if (s != NULL) {
printf("%s\n", s);
}
return 0;
}

/*
** I got it into my head that writing cat using strcat,
** might be cheating in some way, but ...
*/

char *cat(char *s, const char *t)
{
char *tmp;

if (s == NULL) {
tmp = calloc(1, strlen(t) + 1);
} else {
tmp = realloc(s, strlen(s) + strlen(t) + 1);
}
s = tmp;
if (s != NULL) {
strcat(s, t);
}
return s;
}

--
pete

[Flash Gordon]

Roy wrote:

Hi all :
My code below :

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

char *cat(char *s, const char *t)
{
char *tmp;

if (s == NULL)
tmp = realloc(s,strle n(t) + 1);
At this point, the memory pointed to by tmp will be in a random state.
Also you might as well use malloc since you know s is NULL.
else
tmp = realloc(s,strle n(s) + strlen(t) + 1);
if (tmp == NULL) {
fputs("realloc error",stderr);
exit(1);
}
while (*tmp++); // search for '\0' and stop
So the while loop above could do anything if s is NULL, as it is on your
first call.

Also, you have just had the string searched for a '\0' by calling
strlen, so scanning it again seems a bit silly to me.

Also, please don't use // comments on Usenet. They do not survive line
wrapping and, for your information, were not standard in C89 although
they are a common extension. They are standard in C99, but most
implementations that I am aware of are not conforming C99 implementations .
tmp--; //the position of '\0'
while (*tmp++ = *t++) ;
Again, you know the length and could use memcpy which *may* be more
efficient.
s = tmp;
return s;
}

int main()
{
char *tmp;
char *s;

s = NULL;
tmp = cat(s,"oh");
printf("%s\n",t mp);
tmp = cat(s,"haha");
Here you are using s, but s will still be NULL, and loosing the pointer
you obtained by the previous call to cat.
printf("%s\n",t mp);
return 0;
}
my problem is when I run the program the reslut is some blanks. I just
wrote a small routine like strcat and check the realloc and tmp pointer
carefully but found nothing.

Try the following modified version...

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

char *cat(char *s, const char *t)
{
char *tmp;
size_t slen;
size_t tlen = strlen(t);

if (s == NULL)
slen = 0;
else
slen = strlen(s);
tmp = realloc(s,slen + tlen + 1);

if (tmp == NULL) {
free(s); /* improve chances of the fputs not running out of memory */
fputs("realloc error",stderr);
exit(1);
}
memcpy(tmp+slen ,t,tlen);
tmp[slen+tlen]='\0';
return tmp;
}

int main(void)
{
char *tmp;
char *s = NULL;
tmp = cat(s,"oh");
printf("%s\n",t mp);
s = cat(tmp,"haha") ;
printf("%s\n",s );
return 0;
}
--
Flash Gordon
Living in interesting times.
Although my email address says spam, it is real and I read it.

[Michael Knaup]

pete wrote:

pete wrote:

Al Bowers wrote:

>
> pete wrote:

/* I'm taking another shot. */

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

char *cat(char *s, const char *t);

int main(void)
{
char *s;

s = cat(NULL, "oh");
if (s != NULL) {
printf("%s\n", s);
}
s = cat(s, "haha");
if (s != NULL) {
printf("%s\n", s);
}
return 0;
}

/*
** I got it into my head that writing cat using strcat,
** might be cheating in some way, but ...
*/

char *cat(char *s, const char *t)
{
char *tmp;

if (s == NULL) {
tmp = calloc(1, strlen(t) + 1);
} else {
tmp = realloc(s, strlen(s) + strlen(t) + 1);
}
s = tmp;

Why reusing s here, s is only a copy of your s in the main function. So if
you want to change your "main" s you have to use a pointer to a pointer
like All did.
if (s != NULL) {
strcat(s, t);
Maybe the use of malloc/realoc and memcpy is a "little" bit faster than your
solution
}
return s;
}

This one should work

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#if __STDC_VERSION_ _ < 199901L
# define restrict
#endif

char* concat (char **s, restrict const char *t)
{
char *tmp = NULL;

if (NULL == t) {
if (NULL != s) {
tmp = *s;
}
} else {
size_t length = 1u + strlen(t);

if (NULL == s || NULL == *s) {
tmp = malloc (length);
if (NULL != tmp) {
memcpy(tmp, t, length);
if (NULL != s) {
*s = tmp;
}
}
} else {
size_t old_len = strlen(*s);
tmp = realloc (*s, old_len + length);
if (NULL != tmp) {
memcpy (tmp + old_len, t, length);
*s = tmp;
}
}
}
return tmp;
}

int main(void)
{
char *string = NULL;
char *tmp;

concat(&string, "oh");
printf ("*%p == %s\n", string, string);
tmp = string;
do {
concat(&string, "haha");
} while (tmp == string);
printf ("*%p (%zd) == %s\n", string, strlen(string), string);

free (string);

return EXIT_SUCCESS;
}
--
Michael Knaup

[Michael Knaup]

And true you should check against NULL after calling concat

int main(void)
{
char *string = NULL;
char *tmp;

concat(&string, "oh");
if (NULL == string)
return EXIT_FAILURE;
printf ("*%p == %s\n", string, string);
tmp = string;
do { if (NULL == concat(&string, "haha"))
break;
} while (tmp == string);
printf ("*%p (%zd) == %s\n", string, strlen(string), string);

free (string);

return EXIT_SUCCESS;
}

--
Michael Knaup