Question

I am trying to write a function will take char then produces char* which is allocated in heap. How can I do that ?
Note : below code is not work, can you help to fix

Ex:

    char* foo ( char x, char * xc ) {


        xc =  realloc ( xc, 1 + strlen ( xc ) ) ;
        strcat ( xc, x ) ;

    return xc ;
    }

                             p =  heap variable
   foo ( 'a', NULL ) ==>     ------------
                             | 'a'| '\0'|
                             ------------

   foo ( 'b', p )    ===>    --------------------
                             | 'a' | 'b' | '\0' |
                             --------------------

   foo ( 'c', p )    ===>    --------------------------
                             | 'a' | 'b' | 'c' | '\0' |
                             --------------------------

Answer 1

NULL is not a string, therefore yout must not call strlen on it.

size_t len = xc != NULL ? strlen(xc) : 0;
xc = realloc(xc, len + 1 + 1);
xc[len] = c;
xc[len + 1] = '\0';