Duplicate String in C

Question

I have tried to write a function in C that duplicates a string n times. Below is my code, but this does not work. Can someone help me and tell me where I am making a mistake? It should come out something like this:

Input: 4 House Output: HouseHouseHouse

char * repeat(char *str, int times)
 { char *ret = calloc(times, (strlen(str) + 1));
   while (times-- > 0)
     strcat(ret,str);
     char *b;
   b = repeat(str,times);
   printf("%s",b);
   return 0; }

*One* "not work" part is because you must decide to use *either* loops *or* recursion. Not both. — Some programmer dude, Jan 29 '21 at 12:16
*Another* not work part is because you *always* return a null pointer from the function. — Some programmer dude, Jan 29 '21 at 12:17
You should always include what "does not work" means. Provide input and actual output together with expected output. Is your output expected output or current output? — Gerhardh, Jan 29 '21 at 12:18
Here's some advice for doing recursive code - Basically you _always_ need to handle two cases: 1) the base case and 2) the recursive case ("iteration"). — Morten Jensen, Jan 29 '21 at 12:27

score 0 · Answer 1 · answered Jan 29 '21 at 12:28

0

Could you please try this code? I just removed the recursion and added an extra argument output, which will be allocated inside the function repeat

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
void repeat(char *input, char**ouput, int times)
 { *ouput = calloc(times, (strlen(input) + 1));
   while (times-- > 0)
     strcat(*ouput,input);
   printf("%s",*ouput);
 } 
   
int main()
{
    void repeat(char *input, char**ouput, int times);
    char * ouput;
    repeat("hello",&ouput,5);

    return(0);
}

answered Jan 29 '21 at 12:28

Wim

181
3
13

It worked, but how can i edit the code without an extra argument output? I would like to have the function with two arguments. Like this: repeat(char *str, int times). Is this possible? – John Black Jan 29 '21 at 13:53
the allocation will be done inside the function repeat, the system will clean up the data of the function after exit it, so it will be dangerous to return the output as a pointer and use it in your main function you need to keep the input, output and the number of copies as argument and return the length of new output – Wim Jan 29 '21 at 14:15
What exactly is the problem with a function returning an allocated pointer? How does that differ from assigning to a pointer to pointer? The comment is give erroneous advice. Sadly, comments can't be downvoted. – Jonathan Leffler Jan 29 '21 at 14:33
Related : https://stackoverflow.com/questions/766893/how-do-i-modify-a-pointer-that-has-been-passed-into-a-function-in-c – Wim Feb 05 '21 at 14:34
https://stackoverflow.com/questions/1398307/how-can-i-allocate-memory-and-return-it-via-a-pointer-parameter-to-the-calling – Wim Feb 05 '21 at 14:34

Duplicate String in C

1 Answers1