for(inti:{1,2,3})inti=1;// error: redeclaration Temporary range initializer Ifrange-initializerreturns a temporary, its lifetime is extended until the end of the loop, as indicated by binding to the forwarding reference/* range */.
http://en.cppreference.com/w/cpp/language/range-for 语法: for (range_declaration:range_expression)loop_statement for (一个变量名 : 可迭代范围) { //循环语句 } 变量名的类型可以是:容器元素的类型,容器元素的引用类型,auto { auto && __range =range_expression; for (auto __begin =begin_expr,...
Range-Based for loop应该是一种语法糖,实际上编译器应该是当成普通的for循环来处理的。 从cppreference(https://en.cppreference.com/w/cpp/language/range-for)上可以得到印证。 Range-Basedfor loop的一般形式(省略了不相关的部分)实际上等价于下面的for循环 for ( item-declaration : range-initializer ) sta...
所有的STL标准容器都适用于该“范围”,例如vector、string等等。数组也同样可以,只要定义了begin()和end()方法的任何“范围”都可以使用for来循环迭代容器里面的元素,如istream。 语法: for(range_declaration:range_expression)loop_statement 上述代码的效果类似于: (__range,__beginand__endare for exposition onl...
#include <iostream> #include <vector> int main() { std::vector<int> v = {0, 1, 2, 3, 4, 5}; for (const int& i : v) // access by const reference std::cout << i << ' '; std::cout << '\n'; for (auto i : v) // access by value, the type of i is int std...
使用auto声明的变量必须要给初始值,而这里的语法没有给初始值。Range-Based for loop应该是一种语法糖,实际上编译器应该是当成普通的for循环来处理的。 从cppreference(https://en.cppreference.com/w/cpp/language/range-for)上可以得到印证。 Range-Based for loop的一般形式(省略了不相关的部分)实际上等价于...
Use const auto& instead of auto when using type deduction in your range-based for loop when you don’t want to work with copies. The performance penalty of accessing elements through a reference instead of by value is likely to be small, and this insulates us from potentially significant pe...
Here, declaring elem as a reference is important because otherwise the statements in the body of the for loop act on a local copy of the elements in the vector (which sometimes also might be useful). This means that to avoid calling the copy constructor and the destructor for each element...
You should be able to add this easily by changing the return value of get to be a reference, but this would make the code much longer by requiring the addition of non-const methods, and I wanted to focus on the basic structure.Do range-based for loops increase performance?
The last rule (the fallback to the free-standingbegin()andend()functions) allows us to non-invasively adapt an existing container to the range-basedforloop interface. 0.2 类型推断 std::vector<int> v = {1, 2, 3, 5, 7, 11};