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容易犯的小错误
void autoValue(bool age) { //此时，该age会将传入的参数age覆盖掉 auto age = 10; } static void autoValue() { auto age = 10; auto name = std::string("Yt"); auto height = 160.0f; auto weight = 72.0; //typeid是C++中的关键字。typeid的输出结果与平台相关 std::cout << "age is type " << typeid(age).name() << std::endl; std::cout << "name is type " << typeid(name).name() << std::endl; std::cout << "height is type " << typeid(height).name() << std::endl; std::cout << "weight is type " << typeid(weight).name() << std::endl;}static void autoPointer() { auto age = new int(10); //age类型 int* auto name = "Yt"; //name的类型为const char* auto height = new float(160.0f); auto weight = new double(72.0); std::cout << "age is type " << typeid(age).name() << std::endl; std::cout << "name is type " << typeid(name).name() << std::endl; std::cout << "height is type " << typeid(height).name() << std::endl; std::cout << "weight is type " << typeid(weight).name() << std::endl;}
static void newVersionFor() { int ids[] = { 1, 2, 3, 4, 5 }; std::cout << "new version "; for (auto v : ids) { std::cout << v << " "; } std::cout << std::endl; // "\n"; std::cout << "old version "; // old version for (int i = 0; i < sizeof(ids) / sizeof(int); ++i) { std::cout << ids[i] << " "; } std::cout << std::endl; // "\n"; std::vector group; for (int i = 0; i < 4; ++i) group.push_back(i); /* 从效率上分析这三种遍历：最快的是for (auto v : group) for (size_t i = 0; i < group.size(); ++i) 每次循环都要求一下group.size()，进入循环之后还要找一下group[i]的位置 for (std::vector ::const_iterator iter = group.begin(); iter != group.end(); ++iter) { std::cout << *iter << " "; } 每次循环的时候都要比较一下iter != group.end()， 并且还要把相应位置的值（即*iter）提取出来 */ // auto version for (std::vector ::const_iterator iter = group.begin(); iter != group.end(); ++iter) { std::cout << *iter << " "; } std::cout << std::endl; for (size_t i = 0; i < group.size(); ++i) { std::cout << group[i] << " "; } std::cout << std::endl; std::cout << "vector verion : "; for (auto v : group) { v = v * v; } std::cout << std::endl; for (auto& v : group) { //auto求每个元素引用的例子 v = v * v; } //const引用可以防止对传入的参数进行误操作。防止不小心把参数的值修改 for (const auto& v : group) {}}
//自定义的类如何使用新版本的for(auto i : v)class MyVector {public: using GroupType = std::vector ; typedef std::vector GroupType; //只需要定义一下这两个就可以了 GroupType::iterator begin() { return m_group.begin();} GroupType::iterator end() { return m_group.end();}private: GroupType m_group;}; 或者可以这么写
class MyVector {public: using GroupType = std::vector ; typedef std::vector GroupType; //GroupType::iterator begin() { return m_group.begin();} //GroupType::iterator end() { return m_group.end();} GroupType m_group;};MyVector::GroupType::iterator begin(MyVector& v) { return v.m_group.begin();}MyVector::GroupType::iterator end(MyVector& v) { return v.m_group.end();}
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