Summary of fstream, ifstream, and ofsream usage

When writing a program, a piece of code uses fstream to create and read and write hidden files, but some strange problems are discovered: The hidden files are not created at the time of creation, but cannot be read or modified when they exist, the following three types of objects are tested and summarized: 1. Create a file when the test file does not exist.
========================================================== ====================== Fstream FS ("aaa.txt ", ios_base: In) not created
Fstream FS ("aaa.txt", ios_base: Out) Creation
Fstream FS ("aaa.txt", ios_base: trunc) is not created
Fstream FS ("aaa.txt"); // equivalent to downlink
Fstream FS ("aaa.txt", ios_base: In | ios_base: Out) not created
Fstream FS ("aaa.txt", ios_base: In | ios_base: trunc); not created
Fstream FS ("aaa.txt", ios_base: Out | ios_base: trunc); Create
Fstream FS ("aaa.txt", ios_base: In | ios_base: Out | ios_base: trunc); create the above summary:
Fstream is created when the file does not exist
Or use ios_base: out separately
Either ios_base: Out | ios_base: trunc
========================================================== ======================== Ofstream and fstream are not very different,
When you open it, no matter whether or not ios_base: Out is added, it will always be or once ("_ mode | ios_base: Out"), which can be inferred from the previous conclusion, files will be created in the following three cases, and none of them will be created: ofstream ofs ("aaa.txt ")
Ofstream ofs ("aaa.txt", ios_base: trunc)
Ofstream ofs ("aaa.txt", ios_base: In | ios_base: trunc) 2. Test the function of reading hidden files. ========================================================== ====================== Fstream FS ("aaa.txt ", ios_base: In) can
Fstream FS ("aaa.txt", ios_base: Out) cannot
Fstream FS ("aaa.txt", ios_base: trunc) cannot
Fstream FS ("aaa.txt"); // equivalent to downlink
Fstream FS ("aaa.txt", ios_base: In | ios_base: Out) can
Fstream FS ("aaa.txt", ios_base: In | ios_base: trunc); No
Fstream FS ("aaa.txt", ios_base: Out | ios_base: trunc); No
Fstream FS ("aaa.txt", ios_base: In | ios_base: Out | ios_base: trunc); cannot be summarized as follows:
Fstream open hidden files
Or use ios_base: In separately
Or ios_base: trunc is not allowed.
========================================================== ========================
Ifstream and fstream are not much different,
When you open it, no matter whether or not ios_base: In is added, it will always be or once ("_ mode | ios_base: In"), which can be inferred from the previous conclusion, you can open files in either of the following two cases:
Ifstream ifs ("aaa.txt ")
Ifstream ofs ("aaa.txt", ios_base: Out) 3. Read common files========================================================== ====================== Fstream FS ("aaa.txt ", ios_base: In) can
Fstream FS ("aaa.txt", ios_base: Out) can
Fstream FS ("aaa.txt", ios_base: trunc) cannot
Fstream FS ("aaa.txt"); // equivalent to downlink
Fstream FS ("aaa.txt", ios_base: In | ios_base: Out) can
Fstream FS ("aaa.txt", ios_base: In | ios_base: trunc); No
Fstream FS ("aaa.txt", ios_base: Out | ios_base: trunc); Can
Fstream FS ("aaa.txt", ios_base: In | ios_base: Out | ios_base: trunc); can be summarized as follows:
Fstream open common files
Ios_base: trunc must contain both ios_base: Out
========================================================== ========================
Ifstream and fstream are not much different,
When you open it, no matter whether or not ios_base: In is added, it will always be or once ("_ mode | ios_base: In"), which can be inferred from the previous conclusion, in one of the following cases, files cannot be opened, and other files can be:
Ifstream ofs ("aaa.txt", ios_base: trunc)