implicit-conversion

问题 I'm trying to define a new type that can behave essentially like a number (for concreteness, let's say a Double ). I'd like to overload operators on this type and I could do this explicitly, but to avoid repetition, I would like to advantage of the methods in NumericOps, which are defined in terms of the abstract methods in Numeric. My understanding is I should be able to just override the methods in Numeric and get the others for free. Here's the simplest attempt I can think of: class

问题 I'm confused why the following code produces this output: #include <iostream> #include <string> using namespace std; int main() { int i = -1; string s = "abc"; int j = s.size(); int x = 1 % 3; int y = i % j; int z = i % s.size(); cout << s.size() << endl; // 3 cout << x << endl; // 1 cout << y << endl; // -1 cout << z << endl; // 0 } Why is z = 0? Does it have to do with casting? 回答1: So, stripping down your code to a minimal example, you're asking why this prints 0 : #include <iostream>

问题 I'm having an issue with some template stuff that I've narrowed down to the following example (C++17): template <typename T> struct item { operator item<const T> () const { return item<const T>(); } }; void conversionToConstRefWorks (const item<const int> &) { } template <typename T> void butNotWhenTemplated (const item<const T> &) { } int main () { item<int> i; item<const int> ci; // these all compile fine: conversionToConstRefWorks(ci); conversionToConstRefWorks(i); butNotWhenTemplated(ci);

问题 I'm having an issue with some template stuff that I've narrowed down to the following example (C++17): template <typename T> struct item { operator item<const T> () const { return item<const T>(); } }; void conversionToConstRefWorks (const item<const int> &) { } template <typename T> void butNotWhenTemplated (const item<const T> &) { } int main () { item<int> i; item<const int> ci; // these all compile fine: conversionToConstRefWorks(ci); conversionToConstRefWorks(i); butNotWhenTemplated(ci);

问题 This question already has answers here : How does dereferencing of a function pointer happen? (5 answers) Closed last month . According to the GNU C manual, functions can be called using function pointers like so: func (j); /* (*func) (j); would be equivalent. */ So my reasoning here is: func itself is a pointer to the func(int) function. When you call func(j) , you are implicitly accessing the value of the pointer func (you are moving to the memory location where func is), in the same way as

问题 I decided to test compile a project with -Wsign-conversion enabled, to see what warnings would come up, and came across something that doesn't seem right, where gcc behaves differently than clang. Can someone please tell me which is correct? I have a function that takes a size_t param: void func(size_t) {} some other struct struct Test {}; and calling code int i = some_initialiser(); func(sizeof(Test) + static_cast<size_t>(i)); So from my understanding, sizeof returns size_t , and arithmetic

问题 I decided to test compile a project with -Wsign-conversion enabled, to see what warnings would come up, and came across something that doesn't seem right, where gcc behaves differently than clang. Can someone please tell me which is correct? I have a function that takes a size_t param: void func(size_t) {} some other struct struct Test {}; and calling code int i = some_initialiser(); func(sizeof(Test) + static_cast<size_t>(i)); So from my understanding, sizeof returns size_t , and arithmetic

问题 I decided to test compile a project with -Wsign-conversion enabled, to see what warnings would come up, and came across something that doesn't seem right, where gcc behaves differently than clang. Can someone please tell me which is correct? I have a function that takes a size_t param: void func(size_t) {} some other struct struct Test {}; and calling code int i = some_initialiser(); func(sizeof(Test) + static_cast<size_t>(i)); So from my understanding, sizeof returns size_t , and arithmetic

来源： https://stackoverflow.com/questions/64127498/automatic-conversion-from-derived-class-to-base-class-member-variables-type

来源： https://stackoverflow.com/questions/63964610/implicit-view-not-working-is-my-implicit-def-to-blame