Conflating pointers with arrays: C's biggest mistake? (2009)

Re:Conflating pointers with arrays: C's biggest mistake? (2009) by WalterBright on Sunday July 22, 2018 @03:37AM (#17585689)

Off the top of my head (in D syntax):

    char[3] s = "abc";
    char* p = cast(char*)malloc(s.length + 4);
    assert(p != null);
    char[] a = p[0 .. s.length + 4];
    a[0 .. 3] = s[];
    a[3 .. 3+4] = "1234";

It's more verbose than necessary, but I wanted to illustrate the idea. Note how the allocation is turned into a dynamic array.

Note that my proposal is not for a new memory allocation scheme for C, just a way to map data onto arrays.

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Re:Conflating pointers with arrays: C's biggest mistake? (2009) by drfuchs on Sunday July 22, 2018 @03:45AM (#17585714)

You don't seem to understand heap vs. stack. The call to malloc() does a heap allocation, and the question was "without using the heap in any way". If it makes it conceptually easier, how about a solution where the string is simply a global variable? No malloc allowed.

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Re:Conflating pointers with arrays: C's biggest mistake? (2009) by vkazanov on Sunday July 22, 2018 @03:53AM (#17585744)

You don't seem to understand who you are arguing with :-)

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Re:Conflating pointers with arrays: C's biggest mistake? (2009) by geezerjay on Sunday July 22, 2018 @04:34AM (#17585862)

> You don't seem to understand heap vs. stack.

Please check who you are replying to.

https://en.wikipedia.org/wiki/Walter_Bright

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Re:Conflating pointers with arrays: C's biggest mistake? (2009) by jkabrg on Sunday July 22, 2018 @05:25AM (#17585985)

WalterBright posted the following code snippet somewhere above:

     char foo[9]; foo[] = "abc"; foo[3..3+5] = "1234";

`foo` is an array. `foo[3..8]` is a slice, which is an object that does its own bounds-checking. I don't think the heap is used here.

Another explicit example:

  char foo[5] = "abcd"; // still NUL-terminated, carries length aswell
  char[] bar = foo[2..3]; // a fat pointer with length 1
  bar[0] = 'C';
  printf(foo); // abCd
  bar[1] = 'D'// ERROR!!! bar has length 1

Note that the array `foo` is now bounds-checked, which may affect backwards-compatibility. Also, `bar` is no longer null-terminated, which means you can't do printf on it.

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Re:Conflating pointers with arrays: C's biggest mistake? (2009) by WalterBright on Sunday July 22, 2018 @03:49AM (#17585726)

I showed you how to do that in another reply.

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Re:Conflating pointers with arrays: C's biggest mistake? (2009) by acehreli on Sunday July 22, 2018 @09:33AM (#17586636)

Perfectionism is not engineering. Not finding a way to fix every use case that you can come up with is not an excuse to insist on unsafe features that are proven to be disasters in practice.

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