为什么 iostream 头文件没有被包含？
#include <sstream>
using namespace std;
int main()
{
cout << "hi"; // error: undeclared cout
}
据我所知，sstream 类是从 iostream 类派生的，但为什么它没有自动包含在内？
#include <sstream>
using namespace std;
int main()
{
cout << "hi"; // error: undeclared cout
}
From what I have read, sstream class is derived from iostream class but why does it not get included automatically?
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基于 iostream 的类与 iostream 标头不同。标准标头不必相互包含，也可以按任何顺序相互包含。如果您希望使用
#include。The
iostream-based classes are not the same as theiostreamheader. Standard headers do not have to include each other, or may include each other in any order. If you wish to use the contents of<iostream>, you must#include <iostream>.std::sstream派生自std::istream和std::ostream。这意味着您不需要包含std::cout并未在这两个标头中定义。这就是为什么您需要另一个标头std::sstreamis derived from bothstd::istreamandstd::ostream. That means you don't need to include<istream>or<ostream>. However,std::coutis defined in neither of those two headers. That's why you need yet another header,<iostream>.