All arrays (including multidimensional ones) are padding-free. Even if it’s never explicitly mentioned, it can be inferred from sizeof rules. Now, array subscription is a special case of pointer arithmetics, and C99 section 6.5.6, §8 states clearly that behaviour is only defined if the pointer operand and the resulting pointer lie in the same array … Read more
Yes. Per the C++0x FDIS 21.4.7.1/1, std::basic_string::c_str() must return a pointer p such that p + i == &operator[](i) for each i in [0,size()]. This means that given a string s, the pointer returned by s.c_str() must be the same as the address of the initial character in the string (&s[0]).
There is no X object, living or otherwise, so pretending that there is one results in undefined behavior. [intro.object]/1 spells out exhaustively when objects are created: An object is created by a definition ([basic.def]), by a new-expression ([expr.new]), when implicitly changing the active member of a union ([class.union]), or when a temporary object is created … Read more
The paragraph you copied is talking about unsigned types. The behavior is undefined in C++. From the last C++0x draft: The value of E1 << E2 is E1 left-shifted E2 bit positions; vacated bits are zero-filled. If E1 has an unsigned type, the value of the result is E1 × 2E2, reduced modulo one more … Read more
What is color set to according to the standard? Answering with a quote from the C++11 and C++14 Standards: [expr.static.cast]/10 A value of integral or enumeration type can be explicitly converted to an enumeration type. The value is unchanged if the original value is within the range of the enumeration values (7.2). Otherwise, the resulting … Read more
The most recent example I can find is the UNISYS 2200 series, based on UNIVAC, with ones-complement arithmetic. The various models were produced between 1986 and 1997 but the OS was still in active development as late as 2015. They also had a C compiler, as seen here. It seems likely that they may still … Read more
Yes, the argument to toupper needs to be converted to unsigned char to avoid the risk of undefined behavior. The types char, signed char, and unsigned char are three distinct types. char has the same range and representation as either signed char or unsigned char. (Plain char is very commonly signed and able to represent … Read more
A trap representation is a catch-all term used by C99 (IIRC not by C89) to describe bit patterns that fit into the space occupied by a type, but trigger undefined behavior if used as a value of that type. The definition is in section 6.2.6.1p5 (with tentacles into all of 6.2.6) and I’m not going … Read more
UPDATE: Following the discussion in the comments, I added some more evidence at the end of this answer. Disclaimer: I admit this answer is rather speculative. The current formulation of the C++11 Standard, on the other hand, does not seem to allow for a more formal answer. In the context of this Q&A, it has … Read more