我需要编写一个带有重载operator []的类,当运算符[]用于读取或写入数据时,它具有不同的行为.为了给出我想要实现的实际示例,假设我必须编写一个名为PhoneBook的类的实现,该类可以通过以下方式使用:
PhoneBook phoneBook(999999); // 999999 is the default number which should be
// used when calling someone who is not in the phone book
phoneBook["Paul"] = 234657; // adds Paul's number
phoneBook["John"] = 340156; // adds John's number
// next line should print Paul's number 234657
cout << "To call Paul dial " << phoneBook["Paul"] << endl;
// next line should print John's number 340156
cout << "To call John dial " << phoneBook["John"] << endl;
// next line …我想知道如何在不使用虚函数的情况下在 C++ 中声明一个接口。经过一些互联网搜索，我整理了这个解决方案：
#include <type_traits>
using namespace std;
// Definition of a type trait to check if a class defines a member function "bool foo(bool)"
template<typename T, typename = void>
struct has_foo : false_type { };
template<typename T>
struct has_foo<T, typename enable_if<is_same<bool, decltype(std::declval<T>().foo(bool()))>::value, void>::type> : true_type { };
// Definition of a type trait to check if a class defines a member function "void bar()"
template<typename T, typename = void>
struct has_bar : false_type { };
template<typename T>
struct has_bar<T, …我正在试验 C++11（到目前为止我已经使用了旧的 C++）并且我编写了以下代码：
#include <iostream>
#include <vector>
#include <type_traits>
using namespace std;
constexpr bool all_true(){
return true;
}
template <typename Head, typename... Tail>
constexpr bool all_true(Head head, Tail... tail){
static_assert( is_convertible<bool, Head>::value, "all_true arguments must be convertible to bool!");
return static_cast<bool>(head) && all_true(tail...);
}
template<typename T, typename... Args>
void print_as(Args... args){
static_assert( all_true(is_convertible<T,Args>::value...), "all arguments must be convertible to the specified type!");
vector<T> v {static_cast<T>(args)...};
for(T i : v) cout << i << endl;
}
int main(){
print_as<bool>(1, 2, 0, …我想编写一个成员函数来检测实例化对象是否为const.
举一个简单的例子,我们可以考虑以下类定义
class Foo{
public:
void constnessChecker(){
bool isConst;
// MORE CODE GOES HERE...
if (isConst) {
std::cout << "This instance is const! << std::endl;
} else {
std::cout << "This instance is not const! << std::endl;
}
}
};
和以下代码
int main(){
Foo foo1;
Foo const foo2;
foo1.constnessChecker();
foo2.constnessChecker();
}
哪个应该产生
This instance is not const!
This instance is const!
这可能吗？