On: Everything I wish I knew when learning C

[quietbritishjim]

> Declaring a variable or parameter of type T as const T means, roughly, that the variable cannot be modified.

I would add "... cannot be modified through that pointer". (Yes, in fairness, they did say "roughly".) For example consider the following:

    void foo(int* x, const int* y)
    {
        printf("y before: %d\n", *y);
        *x = 3;
        printf("y after: %d\n", *y);
    }

This will print two different values if you have `int i = 1` and you call `foo(&i, &i)`. This is the classic C aliasing rule. The C standard guarantees that this works even under aggresive optimisation (in fact certain optimisations are prevented by this rule), whereas the analogous Fortrain wouldn't be guaranteed to work.

[pafje → quietbritishjim]

You already know this, but I would add that under strict aliasing rules, this is only valid because x and y point to the same type.

The most common example is when y is float* and someone tries to access its bitwise representation via an int*.

(Please correct me if I'm wrong)

https://gist.github.com/shafik/848ae25ee209f698763cffee272a5...

[vardump → quietbritishjim]

A small detail: you probably meant

  printf("y before: %d\n", *y);

[quietbritishjim → vardump]

Oops you're right! Fixed now thanks.

[pm2222 → quietbritishjim]

*y in both printf, right?