why does this work?

[cph]

I saw something like this but I can't remember where

#include <stdio.h>

int main (void)
{
    const unsigned int var = 0xabcd1234;

    printf("%x\n", var);
    ((unsigned char *)&var)[0] = 0xff;
    printf("%x\n", var);

    return(0);
}

it was successfully compiled using gcc with "-Wall", "-W", and "-pedantic" options.
why does it work? I don't understand.
is it one of what they say about C that "you can shoot your own foot" or something like that?

[abachler]

no, you are just recasting a pointer to a different type then manipulating that type. Sure you can shoot yourself fin the foot if you dont know what you are doing though. And it only works if you know what to expect as far as the endianness of the machine.

[cph]

thank you very much

[iMalc]

I saw something like this but I can't remember where

#include <stdio.h>

int main (void)
{
    const unsigned int var = 0xabcd1234;

    printf("%x\n", var);
    ((unsigned char *)&var)[0] = 0xff;
    printf("%x\n", var);

    return(0);
}

it was successfully compiled using gcc with "-Wall", "-W", and "-pedantic" options.
why does it work? I don't understand.
is it one of what they say about C that "you can shoot your own foot" or something like that?

What do you mean by "work"? Anyone saying whether something works or not is only telling us whether it did what they expected or not. It doesn't tell us what they expected it to do to begin with.
So, what did you expect it to do that it actually did do, and why was it surprising?

[quzah]

He means he's changing the value of something declared const. You can do pretty much the same thing in C++. I suppose it's only noteworthy because:

a) it's a "trick".
b) it's a "bug" that could be a huge pain in the ass to track down.


Quzah.

[laserlight]

You can do pretty much the same thing in C++.

Yes, though if you only use C++ style casts, then you need both a const_cast and a reinterpret_cast, either of which should raise alarm bells to a reader.

[iMalc]

Oh, I didn't even notice the const there!

[slingerland3g]

That is cruel