Valgrind complains while using realloc functions? - c

Question

I have implemented my own version of strcat function.
It works fine but valgrind complains.
main()
{
char *src=NULL;
src=(char *) malloc(sizeof(char)*8);
strcpy(src,"sandeep");
xstrcat(src,"pathak");
printf("******FINAL STR IS : %s ********",src);
free(src);
src=NULL;
}
void xstrcat(char *src,const char *dest)
{
int dlen=strlen(dest);
int slen=strlen(src);
int j=0;
int i=0;
char *temp=(char *) realloc(src,(slen+dlen+1)*sizeof(char));
for(j=slen;i<dlen;i++,j++)
{
temp[j]=dest[i];
}
temp[j]='\0';
printf("%s",temp);
}
VALGRIND ERROR :
==31775== Invalid read of size 4
==31775== Invalid read of size 4
==31775== Invalid read of size 1
==31775== Invalid read of size 1
==31775== 14 bytes in 1 blocks are definitely lost in loss record 1 of 1
==31775== at 0x1B9053EE: realloc (vg_replace_malloc.c:197)
==31775== by 0x8048606: xstrcat (in /user/gur27268/Computer_Systems/Socket/DevTest/UTI
==31775== by 0x804850F: main (in /user/gur27268/Computer_Systems/Socket/DevTest/UTIL/a
==31775==
==31775== LEAK SUMMARY:
==31775== definitely lost: 14 bytes in 1 blocks.
==31775== possibly lost: 0 bytes in 0 blocks.
==31775== still reachable: 0 bytes in 0 blocks.
==31775== suppressed: 0 bytes in 0 blocks.
==31775== Reachable blocks (those to which a pointer was found) are not shown.**
==31775== To see them, rerun with: --show-reachable=yes
I have freed src, but using realloc tends to this problem...
Any help would be appreciated..

Answer 1

void xstrcat(char *src,const char *dest) {
You're passing src by value, and xstrcat is working on and modifying its local copy. Any changes you make to src will not be reflected in the calling function.
void xstrcat(char **src,const char *dest) {
// Work with *src
}
...
xstrcat(&src, ...)
This approach lets xstrcat modify main's src variable.
To quote a frequently mentioned sample:
void foo (int x) {
x = 2;
}
void bar (int * x) {
*x = 2;
}
int main() {
foo(9); // foo cannot modify the literal 9
int i = 1;
foo(i); // foo cannot modify the variable i
bar(&9); // This isn't legal - it can't be
bar(&i); // bar modifies i
}