copying void pointer to another void pointer?

Question

I am trying to copy a void pointer to different indexes of another pointer array, things work fine for characters but there appears problem for integer and doubles

Here is my strcture:

typedef struct vector_struct {
 size_t e_sz;
 char e_type;

 #define V_INT 1 
 #define V_DOUBLE 2
 #define V_CHAR 3

 unsigned no_e;
 unsigned cur_cap;
 void* e_array;

}* vector_type;
 //for typecasting
  #define vector_int_at(v,i) (*((int*)v_at(v,i)))
  #define vector_double_at(v,i) (*((double*)v_at(v,i)))
  #define vector_char_at(v,i) (*((char*)v_at(v,i)))

  void* v_at(vector_type v, iterator i) {
    if ( v == NULL )
     fail("v_at() Error: no such vector");
    if ( i == iterator_end )
     i = v->no_e -1;
    if ( i < 0 || i >= v->no_e )
     fail("v_at() Error: no such element in this vector");
    return (v->e_array+i); //return element
   }

I want to copy value into the void* e_array , it can be either integer, character or a double.

void v_push_back(vector_type v, void* new_val){
 if ( v->no_e >= v->cur_cap ) {
    /*** need to expand the array ***/
    v->cur_cap += (v->cur_cap)? v->cur_cap : 2;

    v->e_array = check_a(realloc(v->e_array, sizeof(void*) * v->cur_cap));
    //allocate memory

   }
/*** copy new_val into the array at end position (v->no_e) ***/
   printf("%d  %d %p\n",v->e_sz,v->no_e,v->e_array+(v->no_e *v->e_sz));
    memcpy(
          v->e_array +(v->no_e)*v->e_sz,
          new_val,
          v->e_sz
          );

 (v->no_e)++;
}

I have called this function like this:

c1 = 'o'; v_push_back(vc1,(void*)&c1); //for character
for ( i1 = 0 ; i1 < 10 ; i1++ ){ //for integer
    v_push_back(vi1,(void*)&i1);
}

//I call these like
  for ( i1 = 0 ; i1 < vector_size(vi1) ; i1++ )
   printf(" %ld",vector_int_at(vi1,i1));
  printf("\n");

But it seems things doesn't work for integer but works well for characters but for integers garbage values are copied as shown: enter image description here

Please help me out. thanks

Here the complete project: https://s3.amazonaws.com/assignment.pointers.vectorc.implementation/C-VectorImplementation1.zip

You're probably not taking account of the size of what your void pointer points to. Anyway please provide a [mcve]. — Jabberwocky, May 09 '19 at 12:51
#define vector_int_at(v,i) (*((int*)v_at(v,i))) #define vector_double_at(v,i) (*((double*)v_at(v,i))) #define vector_char_at(v,i) (*((char*)v_at(v,i))) — Faizan Shah, May 09 '19 at 12:53
@FaizanShah: Do not put code in comments. Edit the question to contain a [mcve]. — Eric Postpischil, May 09 '19 at 12:55
You are always allocating `sizeof(void *)` -- `v->e_array = check_a(realloc(v->e_array, sizeof(void*) * v->cur_cap));` perhaps you want `v->e_array = check_a(realloc(v->e_array, v->e_sz * v->cur_cap));` size of current vector. — kiran Biradar, May 09 '19 at 13:00
Please provide a [mcve] (emphasis on _complete_). Something that can be copy/pasted and compiled. — Jabberwocky, May 09 '19 at 13:03
@FaizanShah what is the `v_at` function? (And yes, edit you question!) — Phantom, May 09 '19 at 13:22
here is the path to actual project: https://s3.amazonaws.com/assignment.pointers.vectorc.implementation/C-VectorImplementation1.zip — Faizan Shah, May 09 '19 at 13:26
@FaizanShah No one is going to follow a link to an external zip file. The code should be posted **as text** in the question. If the code is too long, then you need to focus on the "Minimal" part of a MCVE by trimming it down to a sample that reproduces your problem. — dbush, May 09 '19 at 13:36
The code in the linked ZIP file does not match the code in the question. In the ZIP file, `v_push_back` contains `if(v->e_type==V_INT){…`. In the question, it does not. Obviously, one should never expect to get a correct answer why code X is not working by asking about code Y. — Eric Postpischil, May 09 '19 at 14:46

kiran Biradar · Accepted Answer · 2019-05-09T15:19:35.153

Few problems I see,

In order to get ith location of current vector type you need to multiply i with v->e_sz.

void* v_at(vector_type v, iterator i)
{
    .....
    return ((char*)v->e_array+i*v->e_sz); //return element    
}

You are allocating sizeof(void *) what you want is

 v->e_array = check_a(realloc(v->e_array, v->e_sz * v->cur_cap));

Also as of now you are storing address as int but you need to store its value.

void v_push_back(vector_type v, void* new_val){
     if(v->e_type==V_INT){
        //  (v->e_array+(v->no_e))=new_val;
        ((int*)v->e_array)[v->no_e]=*(int*)new_val;
                                    ^------storing its content
     }
}

Without any type checks, simple memcpy should work.

void v_push_back(vector_type v, void* new_val){
    ....
    memcpy(
          v->e_array +(v->no_e)*v->e_sz,
          new_val,
          v->e_sz
          );
       //   *(char*)(v->e_array+v->no_e)=*(char*)new_val;

     (v->no_e)++;
 }

copying void pointer to another void pointer?

1 Answers1