如何在C ++中使用不同的ifstream模式？

Question

1. According to the reference, if I use ifstream infile ( "test.txt" , ifstream::in ); it will Allow input operations on the stream. But what are some of the examples of the "input operations"?
2. Is ifstream infile ( "test.txt" , ifstream::in | ifstream::binary ); the right syntax to use multiple flags?
3. Will it make a difference if I change ifstream:: to iso:: ?

Thank you

Answer 1

1. According to the reference, if I use ifstream infile ( "test.txt" , ifstream::in ); it will Allow input operations on the stream. But what are some of the examples of the "input operations"?

Reading from a file which would mean everything an input stream can support. See istream member functions. Typically, you can do both formatted (using >> ) and unformatted reads (using read ). Remember that ifstream is a specialization of the basic_ifstream template for char type. Depending on your needs, say to read UTF-16 encoded file, you may have to use a different specialization ( wifstream ) or even use a special locale (read this to know more about locales).

2. Is ifstream infile ( "test.txt" , ifstream::in | ifstream::binary ); the right syntax to use multiple flags?

Yes.

3. Will it make a difference if I change ifstream:: to iso:: ?

No.

Answer 2

Stream operations are extraction << and insertion >> . When you do the following assuming file is of fstream type:

file << 5 << 6.5 << "Hello World!"; // insertion of data (output)
file >> x >> y >> str; // exaction of data (input)

You could also, deal with the stream as a binary stream . In that case, it doesn't really look like a " stream " of data but that gives you random access to the data. In some cases you can't use the binary mode, especially if your data is not available like a network stream. Insertion and Extraction, are the two main operations on streams.

ifstream is created as an input stream by default. So, std::ios::in is redundant in this case. You are using the flags correctly.

all streams inherit from ios . So, the flags are available in both places, you can either retrieve them from ios directly or from fstream .