vaxocentrism

[analogy with `ethnocentrism'] A notional disease said to afflict C programmers who persist in coding according to certain assumptions that are valid (esp. under Unix) on VAXen but false elsewhere. Among these are:

 1. The  assumption that dereferencing a null pointer is safe because
    it is all bits 0, and location 0 is readable and 0. Problem: this
    may  instead cause an illegal-address trap on non-VAXen, and even
    on  VAXen  under  OSes  other  than  BSD Unix. Usually this is an
    implicit  assumption  of  sloppy  code  (forgetting  to check the
    pointer  before using it), rather than deliberate exploitation of
    a misfeature.
 2. The assumption that characters are signed.
 3. The  assumption that a pointer to any one type can freely be cast
    into  a pointer to any other type. A stronger form of this is the
    assumption  that all pointers are the same size and format, which
    means  you  don't  have to worry about getting the casts or types
    correct  in  calls. Problem: this fails on word-oriented machines
    or others with multiple pointer formats.
 4. The  assumption  that  the  parameters of a routine are stored in
    memory,  on  a  stack, contiguously, and in strictly ascending or
    descending order. Problem: this fails on many RISC architectures.
 5. The  assumption that pointer and integer types are the same size,
    and  that  pointers  can  be  stuffed into integer variables (and
    vice-versa)  and  drawn  back  out  without  being  truncated  or
    mangled.  Problem:  this  fails  on  segmented  architectures  or
    word-oriented machines with funny pointer formats.
 6. The assumption that a data type of any size may begin at any byte
    address in memory (for example, that you can freely construct and
    dereference  a  pointer  to a word- or greater-sized object at an
    odd  char  address).  Problem:  this  fails  on  many (esp. RISC)
    architectures better optimized for HLL execution speed, and can
    cause an illegal address fault or bus error.
 7. The  (related)  assumption that there is no padding at the end of
    types  and that in an array you can thus step right from the last
    byte  of  a previous component to the first byte of the next one.
    This is not only machine- but compiler-dependent.
 8. The  assumption  that  memory  address space is globally flat and
    that  the  array reference foo[-1] is necessarily valid. Problem:
    this  fails  at  0, or other places on segment-addressed machines
    like  Intel  chips (yes, segmentation is universally considered a
    brain-damaged  way to design machines (see moby), but that is
    a separate issue).
 9. The  assumption  that  objects  can  be arbitrarily large with no
    special   considerations.   Problem:   this  fails  on  segmented
    architectures and under non-virtual-addressing environments.
10. The assumption that the stack can be as large as memory. Problem:
    this  fails  on  segmented  architectures or almost anything else
    without virtual addressing and a paged stack.
11. The  assumption  that bits and addressable units within an object
    are  ordered in the same way and that this order is a constant of
    nature. Problem: this fails on big-endian machines.
12. The  assumption  that  it  is  meaningful  to compare pointers to
    different  objects  not  located  within  the  same  array, or to
    objects   of  different  types.  Problem:  the  former  fails  on
    segmented  architectures, the latter on word-oriented machines or
    others with multiple pointer formats.
13. The  assumption  that an int is 32 bits, or (nearly equivalently)
    the  assumption  that  sizeof(int) == sizeof(long). Problem: this
    fails  on  PDP-11s, 286-based systems and even on 386 and 68000
    systems  under  some  compilers  (and  on 64-bit systems like the
    Alpha, of course).
14. The  assumption  that  argv[] is writable. Problem: this fails in
    many embedded-systems C environments and even under a few flavors
    of Unix.

Note that a programmer can validly be accused of vaxocentrism even if he or she has never seen a VAX. Some of these assumptions (esp. 2--5) were valid on the PDP-11, the original C machine, and became endemic years before the VAX. The terms vaxocentricity and all-the-world's-a-VAX syndrome have been used synonymously.