CODEWITHSUNDEEP
c++
Greg
Greg

Reputation: 23

cin stream position

I am counting the number of non-whitespace characters in the standard input stream (cin) using in.get(). For every character which is not a whitespace character, I increment a counter.

After I'm done counting, I'd like to go back and read the characters. in is a parameter of type std::istream& in (cin in this case).

Here's what I am trying:

std::streampos sp = in.tellg();

while(in)
{
    char c = in.peek();

    if(isspace(c))
        break;

    ++str.mSize;
    in.get();
}

in.seekg(sp);

The value of sp is -1 indicating failure. Why?

Upvotes: 2

Views: 748

Answers (1)

Adam Rosenfield
Adam Rosenfield

Reputation: 400374

Not all input streams are seekable—if stdin is coming from a terminal or a pipe, it's not possible to seek it, forwards or backwards. In that case, you have to buffer the data yourself.

Upvotes: 5

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