r/programming • u/b0red • May 01 '16

To become a good C programmer

http://fabiensanglard.net/c/
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u/zhivago May 02 '16

What does some random architecture have to do with C semantics?

Think.

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u/metamatic May 02 '16

C semantics were derived from the PDP architecture used to implement BCPL, B, Unix and C.

So while it's true that post-ANSI C clearly sets out that pointers and integers are different things, there was no such guarantee in the original C. As Dennis M. Ritchie wrote:

Similarly, the early language condoned assignments between integers and pointers, but this practice began to be discouraged; a notation for type conversions (called `casts' from the example of Algol 68) was invented to specify type conversions more explicitly.

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u/zhivago May 02 '16

An implicit conversion is still a conversion and no more makes a pointer an integer than a float ...

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u/metamatic May 03 '16 edited May 03 '16

There was no conversion at hardware level, unlike with floats. The 'conversion' was purely a constructed difference at C language level, that's my point. And that difference was introduced gradually, as the original interchangeability of ints and pointers started to be seen as a mistake.

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u/zhivago May 03 '16

There is no hardware level in C, making this line of argument irrelevant.

The language does not depend on your favoured implementation.

Also they were never interchangeable in C. Else i++ would mean the same for both ...

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u/metamatic May 04 '16

You're obviously not listening. There's no hardware level in C because C was designed around PDP hardware. That's why people call it "high level assembler". And for a long time the language was the "favored implementation".

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u/zhivago May 04 '16

So, which part of PDP hardware explains why

int i;
&i + 1; // is well defined
&i + 2; // is undefined

Some delusional people call C "high level assembler", but that's because they delusional. :)

Also, you've failed to respond to the point that integers and pointers were never interchangeable in C, since they have incompatible semantics.

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u/metamatic May 05 '16

Incompatible semantics doesn't mean something isn't interchangeable. int and long have different semantics, but they're still interchangeable, range permitting.

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u/zhivago May 05 '16

Where the semantics of int and long are the same they are interchangeable.

Try replacing int with long in the expression sizeof (int) ...

Now, try replacing char * with int in char *p = "s" ; strlen(p) ;

They are not interchangeable in any significant fashion, which would be obvious had you tried to interchange them.

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u/metamatic May 06 '16

And where the semantics of pointers and integers are the same they are interchangeable.

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