Thread: Returning a character pointer and assigning it to another

I am trying to write a program that prints Fibonacci series of characters by replacing 0 with 'a' and 1 with 'b' and next characters accordingly. I am using another function to recursively find out a particular Fibonacci term and return it as a character pointer.

Code:

 #include <stdio.h>#include <string.h>
#include <stdlib.h>
char* FiboS(int);
void D_e() {
    printf("Enter fibbonacci series limit\n");
    int inp;
    scanf("%d", &inp);
    char *fibs;
    //fibs = (char *)malloc(11);
    fibs= FiboS(inp - 1);
    printf("%s\n", fibs);
}
char* FiboS(int i) {
    if (i == 0)
        return "a";
    else if (i == 1)
        return "b";
    char st[10];
    st[0] = '\0';
    strcat(st, FiboS(i - 1));
    strcat(st, FiboS(i - 2));
    //printf("%s\n", st);
    return st;
}

I used printf() function in FiboS() function to ensure that it was returning proper value and it showed that it was working well.
But the code is giving wrong output, the string stored in char pointer fibs is not the same as returned by FiboS() function. I thought it was because fibs was not allocated any memory so I used malloc() but it made no difference. So I used strcpy() function and it worked.
But I don't understand why fibs was not storing the proper value and what strcpy() does different that it works?

Excuse me if I've missed something obvious, I'm a beginner.

Originally Posted by vart

on line 23 you return pointer to local variable which will be invalid as soon as function returns.

So instead - pass the buffer into FiboS function and fill it with data you want to return, make sure you do not go out of array bounds

Thanks for replying, but does it mean that functions in C cannot return any value using local variables? I used them because this works in java.

Originally Posted by amit_s95

Thanks for replying, but does it mean that functions in C cannot return any value using local variables? I used them because this works in java.

You can return using local variable but you cannot return pointers to local variables - the memory pointed to goes out of scope when the function returns hence the pointer becomes invalid. On the other hand, if you return the variable itself, it is copied over.

Originally Posted by Aslaville

you cannot return pointers to local variables

does it include global variables too?
And if its true, how can we return a string in C? Using a global variable?
And if FiboS() is not returning anything valid then how is strcpy() working? Besides, strstr() does return a char pointer, right?
Thanks for answering.