I believe the relevant part of the standard is [res.on.objects], which states If an object of a standard library type is accessed, and the beginning of the object’s lifetime does not happen before the access, or the access does not happen before the end of the object’s lifetime, the behavior is undefined unless otherwise specified. … Read more
Yes, if the uninitialized member is not an unsigned narrow character type or std::byte, then copying a struct containing this indeterminate value with the implicitly defined copy constructor is technically undefined behavior, as it is for copying a variable with indeterminate value of the same type, because of [dcl.init]/12. This applies here, because the implicitly … Read more
Your code has undefined behavior. In void set(){ X = 3; cout << “Before, X = ” << X << endl; nodes.push_back(Node()); cout << “After, X = ” << X << endl; } The access to X is really this->X and this is a pointer to the member of the vector. When you do nodes.push_back(Node()); … Read more
tl;dr: The sequence of the modifications and reads performed in (i+=10)+=10 is well defined in both C++98 and C++11, however in C++98 this is not sufficient to make the behavior defined. In C++98 multiple modifications to the same object without an intervening sequence-point results in undefined behavior, even when the order of those modifications is … Read more
I don’t see any contradiction. Division by zero is undefined, period. There is no mention of “… unless INFINITY is defined” anywhere in the quoted text. Note that nowhere in mathematics it is defined that 1 / 0 = infinity. One might interpret it that way, but it is a personal, “shortcut” style interpretation, rather … Read more
In C++ as in C, shifts are limited to the size (in bits) of the value shifted. For instance, if unsigned int is 32 bits, then a shift of more than 31 is undefined. In practice, a common result is that the 5 least-significant bits of the shift amount are used and the higher order … Read more
UPDATE: This question was the subject of my blog on June 18th, 2012. Thanks for the great question! Why? I want to know if this was a design decision and if so, what prompted it? You are essentially asking for the minutes of the meeting of the ANSI C design committee, and I don’t have … Read more
You have no right to get a segmentation fault. For that matter, a segmentation fault isn’t even part of C++. Your program is removing all elements from the vector, and you’re illegally accessing the container out of bounds. This is undefined behaviour, which means anything can happen. And indeed, something happened.
Does the definition int a = 0, b = a++, c = a++; have defined behavior in C? Yes, because C 2018 6.8 3 says these initializations (not all, see bottom) are evaluated in the order they appear: … The initializers of objects that have automatic storage duration, and the variable length array declarators of … Read more
This is an odd aspect of C++’s lifetime rules. [basic.life]/1 tells us that an object’s lifetime ends: if T is a class type with a non-trivial destructor ([class.dtor]), the destructor call starts, or the storage which the object occupies is released, or is reused by an object that is not nested within o ([intro.object]). Emphasis … Read more