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  • /vak`soh-sen'trizm/ n. [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 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