Thread: Does realloc save the previous buffer data?

Hello, maybe that's a stupid question, but does the realloc function save the previous saved data into the reallocated buffer?

Code:

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

int main()
{
char *bff,*tmp;
int l;

l=strlen("hello")+1;
if(!(bff=malloc(l))) {getch();return 0;}
memset(bff,0,l);
sprintf(bff,"hello");

l=strlen(bff)+strlen(" world")+1;
if((tmp=realloc(bff,l)))//here's my question
    {
    bff=tmp;
    strcat(bff," world");
    }

printf("%s",bff);

memset(bff,0,l);
free(bff);

getchar();
return 0;
}

Output:
hello world

I have tested that code (with dev-cpp / mingw) several times and it have worked, but I'm not sure if that works because that's a right coding practice or because somekind of coincidence have done it. I have tested some more and find that the pointer to a reallocated buffer after the reallocation have no data but it isn't a null pointer, but the data contents is still there in the memory, and tmp have the pointer to that memory:

Code:

//modification on the previous code
if((tmp=realloc(bff,l)))
    {
    printf("BFF=%s\nTMP=%s\n%s\n",bff,tmp,((!bff)?"NULL BFF":"NOT NULL BFF"));
    bff=tmp;
    strcat(bff," world");
    }

Output:
BFF=
TMP=hello
NOT NULL BFF

So realloc quits the pointer from the bff and asign it to the tmp (no?), the data stored previously in that point is still in that point that now is accessible from tmp, because of that I have to 'bff=tmp' to re-set the pointer to the main buffer. That will ensure that the data previously saved there will still be there after a reallocation (in all the cases)? Or is not a safe method? Or there's some situation that can fail that?

Thank's in advance
Niara

You could just look up what realloc is supposed to do.

BTW: getch() is non-standard. I wouldn't use it if I were you. getchar() is good.

Better to use gets() ...

Code:

char dummy[2];
gets(dummy);

Because if we do:

Code:

/* ... */
getchar();
/* ... */
char dummy[2];
gets(dummy);

Your program goes well...

Hi thank's all for your time and help.

And sorry for the indentation and the getch (I don't know why I have used it, you can see that at the end I have used the getchar() instead; surely I was in a hurry to post the question ). I'll have in mind all your advices, and I'll try to apply (that's not the first post where someone invite me to do a clearer indentation, and to avoid the getch()).

Thank's
Niara