How to write recursive function that copies a string to a location?

Question

any ideas about how to write a RECURSIVE function that gets 2 parameters : first is an address d (a location of char). second is a string. The function copies the string s to a location starting at d. The function returns d as a result ! can we do it without strcpy ?

    copy_r(char *s, char *d)
{
    *d = *s;
    if(*s)return copy_r(++s, ++d);
}

where is the mistake ? (found ) put still there is a problem ! what if the location d overlaps some location that is already occupied by s ?
this for example strcpy(p1, "abcdefghijklomopqrstuvwqyz"); printf(copy_r(p1, p1+10));doesnt work –

output should be klomopqrstuvwqyz

Yes it can be done without `strcpy`, and it can be done recursively. — Some programmer dude, Feb 05 '13 at 13:20
This is the same as asking "can `strcpy()` be implemented in C?", and of course the answer is yes. — unwind, Feb 05 '13 at 13:21
hint: look at the [2 lines recursive function](http://stackoverflow.com/questions/14702877/recursive-form-of-changing-multiple-spaces-to-one-space/14704571#14704571) I wrote in your previous question... by modifying it *a bit* you have the result — Déjà vu, Feb 05 '13 at 13:27
im not so good at that im just trying to see some examples to practice ! any help will be appreciated — user2042145, Feb 05 '13 at 13:28
@user2042145 - Just try "recursive strcpy C" in Google, the first hit I see is exactly what you want. — Mike, Feb 05 '13 at 13:36
@Mike *give a man an answer and you feed him for a day. Teach a man to google and you feed him for a lifetime* — Déjà vu, Feb 05 '13 at 13:42

score 1 · Answer 1 · answered Feb 05 '13 at 14:14

1

where is the mistake

Well, there isn't any mistake, this code sample works correctly... the only issue I see is that it doesn't work exactly as you expect. You mentioned you wanted it to The function returns d as a result and you don't have it doing that.

The code currently takes s and copies the contents into d so if you had something like:

char * str = "hello";
char * ptr = malloc(6);
copy_r(str, ptr);
// now ptr has "hello" too

answered Feb 05 '13 at 14:14

Mike

47,263
29
113
177

will adding a halting condition like if(s=='\0') return d; will it work ? – user2042145 Feb 05 '13 at 14:24

score 1 · Answer 2 · answered Feb 05 '13 at 14:31

1

Your copy logic is perfect. Just that you are not returning any value (d)...

This should work:

char* copy_r(char *s, char *d)
{
    *d = *s;
    if(*s)
      return copy_r(s + 1, d + 1 ) - 1 ; //-1 is to take care of d+1 part
    else
      return d;
}

sample usage:

int main(){
    char src[]="hello world";
    char dest[50];

    char* t=copy_r(src,dest);

    printf("%s\n%s\n",t,dest); //t==dest. thus you don't really have to return anything from the function.
    return 0;
}

answered Feb 05 '13 at 14:31

anishsane

20,270
5
40
73

thanks ! put still there is a problem ! what if the location d overlaps some location that is already occupied by s ? – user2042145 Feb 05 '13 at 17:13
strcpy(p1, "abcdefghijklomopqrstuvwqyz"); printf(copy_r(p1, p1+10)); this for example doesnt work – user2042145 Feb 05 '13 at 17:15
So for this example, what is the expected output? – anishsane Feb 06 '13 at 04:21
output is klomopqrstuvwqyz – user2042145 Feb 06 '13 at 10:34
& why do you think expectation `klomopqrstuvwqyz` is correct (read:appropriate/right)? this does not have copy of source... – anishsane Feb 06 '13 at 12:11

How to write recursive function that copies a string to a location?

2 Answers2