Yes, the code is legal in C++11 because the storage for std::string is guaranteed to be contiguous and your code avoids overwriting the terminating NULL character (or value initialized CharT). From N3337, §21.4.5 [string.access] const_reference operator[](size_type pos) const; reference operator[](size_type pos); 1 Requires: pos <= size(). 2 Returns: *(begin() + pos) if pos < size(). … Read more
Is it guaranteed by the law? No. C++ says nothing about the representation of bool values. Is it guaranteed by practical reality? Yes. I mean, if you wish to find a C++ implementation that does not represent boolean false as a sequence of zeroes, I shall wish you luck. Given that false must implicitly convert … Read more
Unfortunately, this is UB, if I interpret the wording correct (in any case, it’s not allowed): §21.4.5 [string.access] p2 Returns: *(begin() + pos) if pos < size(), otherwise a reference to an object of type T with value charT(); the referenced value shall not be modified. (Editorial error that it says T not charT.) .data() … Read more
The standard doesn’t quite spell it out, but v.erase(q) is defined, “Erases the element pointed to by q” in [sequence.reqmts]. This means that q must actually point to an element, which the end iterator doesn’t. Passing in the end iterator is undefined behavior. Unfortunately, you need to write: auto it = std::find(…); if (it != … Read more
Brace elision applies, but not in C++11. In C++14, they will apply because of http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#1270 . If you are lucky, Clang will backport that to their C++11 mode (let’s hope they will!).
This boils down to whether or not a lambda’s type differs across translation units. If it does, it may affect template argument deduction and potentially cause different functions to be called – in what are meant to be consistent definitions. That would violate the ODR (see below). However, that isn’t intended. In fact, this problem … Read more
Does the existence of such a statement in a given program mean that the whole program is undefined or that behavior only becomes undefined once control flow hits this statement? Neither. The first condition is too strong and the second is too weak. Object access are sometimes sequenced, but the standard describes the behavior of … Read more
The C11 standard says this, 6.8.5/6: An iteration statement whose controlling expression is not a constant expression,156) that performs no input/output operations, does not access volatile objects, and performs no synchronization or atomic operations in its body, controlling expression, or (in the case of a for statement) its expression-3, may be assumed by the implementation … Read more
In the C Standard, only option (1) is initialization. In programming jargon, both may be considered initialization. Your question is really asking about the meanings of words. It’s normal for people to use words with various common meanings, instead of switching terminology for particular languages. Another example is “pass by reference”. Does C have pass … Read more
The lvalue you use to access the stored value of y is not *reinterpret_cast<Foo*>(&y), of type Foo, but it is reinterpret_cast<Foo*>(&y)->x, which has the type float. Accessing a float using an lvalue of type float is fine. In C++, you can not “access the value of a union or struct” (as whole), you can only … Read more