for an array a , is a same as &a

This is a discussion on for an array a , is a same as &a within the C Programming forums, part of the General Programming Boards category; Code: #include <stdio.h> void display(int* arr,int len){ int i; for(i = 0; i < len; ++i){ printf("%d ",arr[i]); printf("\n"); } ...

  1. #1
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    for an array a , is a same as &a

    Code:
    #include <stdio.h>
    void display(int* arr,int len){
        int i;
        for(i = 0; i < len; ++i){
    	printf("%d ",arr[i]);
    	printf("\n");
        }
    }
    main()
    {
        int arr[] = {1,2,3};
        printf("%d  %d\n",arr,&arr);
    }
    are the two arr and &arr same ? , can they be used interchangeably ?
    if not what is the difference ?
    gcc gives this warning:

    test23.c: In function `main':
    test23.c:13: warning: passing arg 1 of `display' from incompatible pointer type

  2. #2
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    Code:
    #include <stdio.h>
    void display(int* arr,int len){
        int i;
        for(i = 0; i < len; ++i){
    	printf("%d ",arr[i]);
    	printf("\n");
        }
    }
    main()
    {
        int arr[] = {1,2,3};
        printf("%d  %d\n",arr,&arr);
        display(&arr,3);
        display(arr,3);
    }
    This is the code i am referring to

  3. #3
    Code Goddess Prelude's Avatar
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    >are the two arr and &arr same ? , can they be used interchangeably ?
    No, and no. The fact that your compiler warns you about it should be a hint that they're not compatible types.

    >if not what is the difference ?
    A level of indirection. For the following array:
    Code:
    int a[10];
    a is almost always treated as the address of the first element (&a[0]), but &a is treated as the address of the array as a whole. The address may be the same, but the types are different. a is a pointer to int and &a is a pointer to an array of ten int.

    To use both, you need two different functions:
    Code:
    #include <stdio.h>
    void display1(int* arr,int len){
      int i;
      printf("display1: ");
      for(i = 0; i < len; ++i)
        printf("%d ",arr[i]);
      printf("\n");
    }
    void display2(int (*arr)[3],int len){
      int i;
      printf("display2: ");
      for(i = 0; i < len; ++i)
        printf("%d ",(*arr)[i]);
      printf("\n");
    }
    int main(void)
    {
      int arr[] = {1,2,3};
      printf("%d  %d\n",arr,&arr);
      display2(&arr,3);
      display1(arr,3);
      return 0;
    }
    My best code is written with the delete key.

  4. #4
    and the hat of wrongness Salem's Avatar
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    > are the two arr and &arr same ?
    They're the same by value, but the types are different.
    Compare a pointer to a struct and a pointer to the first element of a struct - same value, different type.

    > can they be used interchangeably ?
    No.

    > if not what is the difference ?
    arr is a pointer to the first element of the array (like &arr[0] is), and &arr is a pointer to the whole array.

    void display(int (*arr)[3],int len);
    Would be the prototype of the function for passing a pointer to the whole array.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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  5. #5
    and the hat of wrongness Salem's Avatar
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    Spooky
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  6. #6
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    thanks a lot

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