How to use different ifstream modes in c++?

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.