language-lawyer

问题 I noticed today that in the example code: void print(unsigned short a) { std::cout << a << std::endl; } Initialization and use works like this: print(short (5)); But not like this: print(unsigned short(6)); main.cpp:16:8: error: expected primary-expression before 'unsigned' print(unsigned short(6)); And it's not to do with the type since this also works: typedef unsigned short ushort; print(ushort (6)); Live example. So I went searching for what the standard says about value initialization.

问题 Is this defined behaviour? *p += *p--; And, if it is, is it equivalent to { p[0] += p[0]; --p; } or to { p[-1] = p[0]; --p; } ? I'm guessing the being defined or not depends on whether += has an implicit sequence point and, if it has, my guess is that the second block should be the correct one. EDIT: I think it's not a duplicate of the suggested question because the main question there is what are sequence points and how do the affect behaviour. In my case I have clear idea of what a sequence

问题 I just asked this question: Can I get the Owning Object of a Member Function Template Parameter? and Yakk - Adam Nevraumont's answer had the code: template<class T> struct get_memfun_class; template<class R, class T, class...Args> struct get_memfun_class<R(T::*)(Args...)> { using type=T; }; These is clearly an initial declaration and then a specialization of struct get_memfun_class . But I find myself uncertain: Can specializations have a different number of template parameters? For example,

问题 Closed . This question is opinion-based. It is not currently accepting answers. Want to improve this question? Update the question so it can be answered with facts and citations by editing this post. Closed 5 years ago . Background Some CPUs, such as the Atmel AVR, have a general purpose register file that is also addressable as part of main memory -- see Figure 7-2 in section 7.4 and the paragraph after the figure. What was WG14 thinking? Given this, why did the C committee choose to make

问题 Closed . This question is opinion-based. It is not currently accepting answers. Want to improve this question? Update the question so it can be answered with facts and citations by editing this post. Closed 5 years ago . Background Some CPUs, such as the Atmel AVR, have a general purpose register file that is also addressable as part of main memory -- see Figure 7-2 in section 7.4 and the paragraph after the figure. What was WG14 thinking? Given this, why did the C committee choose to make

问题 I recently found out that the types of parameters in a non-defining function declaration may be of incomplete types. This is very exciting. class A; class B { B(A a); // Legal! Wow! }; The type is required to be complete only for the definition: B::B(A a) {}; // error: ‘a’ has incomplete type I've been trying to pin down the legalese for this, but my searches through C++11 for "[in]complete type" have yielded nothing of much interest, leading me to assume that these semantics are defined

问题 The following program // Code has taken from http://ideone.com/AXClWb #include <stdio.h> #include <string.h> #define SIZE1 5 #define SIZE2 10 #define SIZE3 15 int main(void){ char a[SIZE1] = "Hello"; char b[SIZE2] = " World"; char res[SIZE3] = {0}; for (int i=0 ; i<SIZE1 ; i++){ res[i] = a[i]; } strcat(res, b); printf("The new string is: %s\n",res); return 0; } has well defined behavior. As per the requirement, source string b is null terminated. But what would be the behavior if the line

问题 I need a language lawyer with authoritative sources. Take a look at the following test program which compiles cleanly under gcc: #include <stdio.h> void foo(int *a) { a[98] = 0xFEADFACE; } void bar(int b[]) { *(b+498) = 0xFEADFACE; } int main(int argc, char **argv) { int a[100], b[500], *a_p; *(a+99) = 0xDEADBEEF; *(b+499) = *(a+99); foo(a); bar(b); printf("a[98] == %X\na[99] == %X\n", a[98], a[99]); printf("b[498] == %X\nb[499] == %X\n", b[498], b[499]); a_p = a+98; *a_p = 0xDEADFACE; printf

问题 Consider the following simple code that makes use of new (I am aware there is no delete[] , but it does not pertain to this question): int main() { int* mem = new int[100]; return 0; } Is the compiler allowed to optimize out the new call? In my research, g++ (5.2.0) and Visual Studio 2015 do not optimize out the new call, while clang (3.0+) does. All tests have been made with full optimizations enabled (-O3 for g++ and clang, Release mode for Visual Studio). Isn't new making a system call

问题 Quoting [thread.mutex.recursive]: A thread that owns a recursive_mutex object may acquire additional levels of ownership by calling lock() or try_lock() on that object. It is unspecified how many levels of ownership may be acquired by a single thread. If a thread has already acquired the maximum level of ownership for a recursive_mutex object, additional calls to try_lock() shall fail, and additional calls to lock() shall throw an exception of type system_error . Is there a lower bound