auto

这种写法错误，迭代器不能向下递减，小于零后，k的值会越界变得非常大 可以使用reverse()包含在algorihtm 头文件下的函数将数据反转 来源： https://www.cnblogs.com/zxzmnh/p/11724134.html

const int ci = 10; auto i = ci; // i will be "int" instead of "const int" i = 20; I am wondering why auto is designed for this kind of behaviour? why the type i is "int" instead of "const int" ? what is the concern here? I think understand why will help us to remember it Praetorian auto mostly follows the same type deduction rules as template argument deduction. The only difference is that auto will deduce std::initializer_list from a braced-init-list in some cases, while template argument deduction doesn't do this. From N3337, §7.1.6.4 [dcl.spec.auto] 6 ... The type deduced for the variable d

该vector只能容纳标准库中string类， 直接上代码了，StrVec.h文件内容为: 1 #ifndef STRVEC_H 2 #define STRVEC_H 3 4 #include<iostream> 5 #include<string> 6 #include<memory> 7 using namespace std; 8 class StrVec{ 9 public: 10 // 默认构造函数 11 StrVec():elements(nullptr),first_free(nullptr),cap(nullptr) 12 { 13 14 } 15 //拷贝构造函数 16 StrVec(const StrVec& ); 17 //拷贝赋值运算符 18 StrVec& operator=(const StrVec&); 19 ~StrVec(); 20 void push_back(const string&); 21 size_t size() const { return first_free - elements ; } 22 size_t capacity() const { return cap - elements ;} 23 string* begin() const { return elements ;} 24 string* end() const

I have: #include <cstdlib> #include <vector> using namespace std; int main() { auto a = -SOME_CONST_MAX; vector<auto> myVec {a, a, a, a}; } I don't know the type of the SOME_CONST_MAX but I want to make a vector of the type of -SOME_CONST_MAX . I assumed vector<auto> would work as it will deduce from type of a . I'm getting these errors running: g++ -std=c++14 main.cpp main.cpp:9:9: error: invalid use of ‘auto’ vector<auto> myVec {a, a, a, a}; ^ main.cpp:9:13: error: template argument 1 is invalid vector<auto> myVec {a, a, a, a}; ^ main.cpp:9:13: error: template argument 2 is invalid main.cpp

Let's say I have a simple c++ class that contains a private member and a getter: class MyClass { private: double m_testValue = 1; public: double& getTestValue(){return m_testValue;} } Now let's say I want to call the getter to get my reference and edit this value (and printing before / after values) auto testVal = myClassInstance.getTestValue(); std::cout << myClassInstance.getTestValue() << std::endl; std::cout << testVal << std::endl; testVal = 3; std::cout << myClassInstance.getTestValue() << std::endl; std::cout << testVal << std::endl; The output is 1 1 1 3 This is not exactly what I