How to clear a file using file I/O streams without closing it?

Question

C++ / C#

I want to open a file, write a line to it, then, without closing the file, start writing again, so that the old information is deleted:

std::ofstream file;
file.open("file.txt", std::ios_base::in | std::ios_base::out);
file << "AA";
file.seekp(std::ios::beg);
file << "1";
file.close();

As a result, I get 1Aand should be1

Answer 1

Exactly the way you want - no way.
How to clear the content of a file after it is ope...
How to truncate a file while it is open with fstream