Pointer to lowest address in memory

Question

Possible Duplicate:
Detecting endianness programmatically in a C++ program

I'm trying to check if I'm running a little or big endian OS.

int main()
{
    int i = 1; 
    unsigned char b = i; 
    char *c = reinterpret_cast<char*>(&i); // line 5

    cout << "Processor identified as: " << endl;

    if (*c == b) 
        cout << "Little endian" << endl;
    else
        cout << "Big endian" << endl;
}

I'm not sure if casting an int* to char* pointer in line 5 is guaranteed to return a lowest address. Am I doing it right?

You are looking for this: http://stackoverflow.com/questions/1001307/detecting-endianness-programmatically-in-a-c-program no need for pointers here — David Heffernan, Dec 06 '11 at 20:14
My question is about `int to char*` not "How to check endianness?" — user103214, Dec 06 '11 at 20:18

score 0 · Answer 1 · answered Dec 06 '11 at 20:14

0

It might give you the bottom address of the call stack (of the main thread).

But heap addresses may compare lower (or upper) to that address.

Also, stack growth direction is orthogonoal to endianess.

answered Dec 06 '11 at 20:14

Basile Starynkevitch

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This does not make sense as an answer, reread the question, it is actually asking whether the reinterpret is guaranteed to return the lowest address of the variable. – David Rodríguez - dribeas Dec 06 '11 at 20:18

bdonlan · Answer 2 · 2011-12-06T20:21:14.980

0

The C++ standard does not place any restrictions on the byte content of an integer. You may find some systems that are neither little nor big endian - eg, the PDP-11 used a format in which 0x0A0B0C0D was stored as 0B 0A 0D 0C. It's also allowed for there not to be any 0x01 byte at all in the representation for 1.

As for whether the cast will return the lowest byte in the int, it will. However, again, the content of this byte is not well-defined by the C++ specification.

edited Dec 06 '11 at 20:21

answered Dec 06 '11 at 20:15

bdonlan

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Unrelated, the question is whether the reinterpret cast will retrieve the first byte of the integer, not about endianness ingeneral – David Rodríguez - dribeas Dec 06 '11 at 20:19

score 0 · Answer 3 · answered Dec 06 '11 at 20:23

0

Your char will have the same address as your int, which will be the lowest address of any byte in the int. In don't know if this is actually guaranteed, but it's true on every system I've ever used.

answered Dec 06 '11 at 20:23

John Gordon

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Pointer to lowest address in memory

3 Answers3