C++ 将 ifstream 转换为 istream
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Convert ifstream to istream
提问by Anonymous
How would one go about casting a ifstream into a istream. I figure since ifstream is a child of istream I should be able to do so but I have been having problems with such a task.
如何将 ifstream 转换为 istream。我想既然 ifstream 是 istream 的孩子，我应该能够这样做，但我在执行这样的任务时遇到了问题。
std::istream & inputStr = std::cin;
std::ostream & outputStr = std::cout;
if(argc == 3){
std::fstream inputFile;
inputFile.open(argv[1], std::fstream::in);
if(!inputFile){
std::cerr << "Error opening input file";
exit(1);
}
inputStr = inputFile;
.....
}
回答by Cheers and hth. - Alf
No cast is necessary.
不需要演员表。
#include <fstream>
int main()
{
using namespace std;
ifstream f;
istream& s = f;
}
回答by Steve Guidi
Try:
尝试：
std::ifstream* myStream;
std::istream* myOtherStream = static_cast<std::istream*>(myStream);
myOtherStream = myStream; // implicit cast since types are related.
The same works if you have a reference (&) to the stream type as well. static_castis preferred in this case as the cast is done at compile-time, allowing the compiler to report an error if the cast is not possible (i.e. istreamwere not a base type of ifstream).
如果您也有对流类型的引用 (&)，则同样有效。 static_cast在这种情况下是首选，因为强制转换是在编译时完成的，如果强制转换是不可能的（即istream不是 的基本类型ifstream），则允许编译器报告错误。
Additionally, and you probably already know this, you can pass a pointer/reference to an ifstreamto any function accepting a pointer/reference to a istream. For example, the following is allowed by the language:
此外，您可能已经知道这一点，您可以将指向 的指针/引用传递ifstream给任何接受指向 的指针/引用的函数istream。例如，语言允许以下内容：
void processStream(const std::istream& stream);
std::ifstream* myStream;
processStream(*myStream);
回答by Neil
std::istream *istreamObj = dynamic_cast<std::istream *>(&ifStreamObj)
