reallocating memory doesn't work in c

Question

What I'm trying to do in my program is to copy the content of one string to another, in reverse. This part of the program works.

However, I don't want to limit the user for input, so I want to use malloc and realloc. This is my code:

#include <stdio.h>
#include <stdlib.h>
/*copy one string to another, in reverse*/
void copyStr(char *p, char *h){

   int i=0,j=0;
   int length=0;
   length=strlen(p); int l=length;
   for (i=0; i<length; i++){
       h[i]=p[l-1];
       l--;
   }
   char *temp=&h[0];
   for (i=0; i<length; i++){
       printf("%c",temp[i]);
   }


}
main(){
    printf("please enter a string\n");
    char c; int i=0; int end=10;
    /*allocate initial memory*/
    char *p=(char*)malloc(sizeof(end)); char *temp=p;
    while (c!='\n')
    {
        /*reallocate if needed*/
        if (i==(end-1)){
            end*=2;
             temp = realloc(p,end*sizeof(temp));
            if (temp!=NULL){
                /*this is for myself, to see what the error was*/
                printf("error allocating\n");
                exit(1);
            }
            else
                free(p);
        }
        c=getchar();
        p[i]=c;
        i++;
    }

    char h [sizeof(p)];
    copyStr(p,h);
}

I found out that the realloc function doesn't work and so I am asking for your help.

The program works if the input is very short (i.e 3 chars). If it longer than 10 letters, it will not reallocate memory. If it longer than 5, it will print reversly but will send me a message called "stack smashed". Thank you.

Answer 1

In fact, there are some little tricks to change :

• the *temp=realloc(... should become temp=realloc(...
• The fact that temp!=NULL is the normal behavior of realloc().
• do not forget to change p after the realloc operation if you use it after.
• sizeof(p) is the size of a pointer, that is 4 or 8... I turned it into char h [sizeof(char)*(i+1)];
• i also added the \0 character at the end of the string. This is useful if you wish to print it or use strlen() and #include string.h. Then you can printf("the result is :\n%s \n",h);

Here goes the code :

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/*copy one string to another, in reverse*/
void copyStr(char *p, char *h){

    int i=0,j=0;
    int length=0;
    length=strlen(p); int l=length;
    for (i=0; i<length; i++){
        h[i]=p[l-1];
        l--;
    }
    //keep end-of-string character
    h[length+1]='\0';
    /* char *temp=&h[0];
   for (i=0; i<length; i++){
       printf("%c",temp[i]);
   }*/
    printf("the result is :\n%s \n",h);



}
main(){
    printf("please enter a string\n");
    char c; int i=0; int end=10;
    /*allocate initial memory*/
    char *p=(char*)malloc(sizeof(end)); char *temp=p;
    //signaling end of string
    p[0]='\0';
    while (c!='\n' && c!=EOF)
    {
        /*reallocate if needed*/
        if (i==(end-2)){
            end*=2;
            temp=(char*)realloc(p,end*sizeof(char));
            if (temp==NULL){
                /*this is for myself, to see what the error was*/
                printf("error allocating\n");
                exit(1);
            }
            else{
                p=temp;
                printf("ok here\n");
            }
        }
        c=getchar();
        p[i]=c;
        i++;
    }
    //signaling end of string 
    p[i+1]='\0';

    printf("INVERTING STRING\n");
    char h [sizeof(char)*(i+1)];
    copyStr(p,h);

           free(p);
}

! enif krow ot smees ti

Bye,

Francis