[c++primer][08]标准IO库

int ival;
// read cin and test only for EOF; loop is executed even if there are other IO failures
while (cin >> ival, !cin.eof()) {
    if (cin.bad()) // input stream is corrupted; bail out
        throw runtime_error("IO stream corrupted");
    if (cin.fail()) { // bad input
        cerr<< "bad data, try again"; // warn the user
        cin.clear(istream::failbit); // reset the stream
        continue; // get next input
    }
// ok to process ival
}    

// remember current state of cin
istream::iostate old_state = cin.rdstate();
cin.clear();
process_input(); // use cin
cin.clear(old_state); // now reset cin to old state

// sets both the badbit and the failbit
is.setstate(ifstream::badbit | ifstream::failbit);

cout << "hi!" << flush; // flushes the buffer; adds no data
cout << "hi!" << ends; // inserts a null, then flushes the buffer
cout << "hi!" << endl; // inserts a newline, then flushes the buffer

cout << unitbuf << "first" << " second" << nounitbuf;
//is equivalent to writing
cout << "first" << flush << " second" << flush;

cin.tie(&cout); // illustration only: the library ties cin and cout for us
ostream *old_tie = cin.tie();
cin.tie(0); // break tie to cout, cout no longer flushed when cin is read
cin.tie(&cerr); // ties cin and cerr, not necessarily a good idea!
// ...
cin.tie(0); // break tie between cin and cerr
cin.tie(old_tie); // restablish normal tie between cin and cout

// construct an ifstream and bind it to the file named ifile
ifstream infile(ifile.c_str());

ifstream infile; // unbound input file stream
infile.open("in"); // open file named "in" in the current directory

// check that the open succeeded
if (!infile) {
    cerr << "error: unable to open input file: "
        << ifile << endl;
    return -1;
}

ifstream infile("in"); // opens file named "in" for reading
infile.close(); // closes "in"
infile.open("next"); // opens file named "next" for reading

ifstream input;
vector<string>::const_iterator it = files.begin();
// for each file in the vector
while (it != files.end()) {
    input.open(it->c_str()); // open the file
    // if the file is ok, read and "process" the input
    if (!input)
        break; // error: bail out!
    while(input >> s) // do the work on this file
        process(s);
    input.close(); // close file when we're done with it
    input.clear(); // reset state to ok
    ++it; // increment iterator to get next file
}    

// opens in binding it to the given file
ifstream& open_file(ifstream &in, const string &file)
{
    in.close(); // close in case it was already open
    in.clear(); // clear any existing errors
    // if the open fails, the stream will be in an invalid state
    in.open(file.c_str()); // open the file we were given
    return in; // condition state is good if open succeeded
}

string line, word; // will hold a line and word from input, respectively
while (getline(cin, line)) { // read a line from the input into line
    // do per-line processing
    istringstream stream(line); // bind to stream to the line we read
    while (stream >> word){ // read a word from line
        // do per-word processing
    }
}

int val1 = 512, val2 = 1024;
ostringstream format_message;
// ok: converts values to a string representation
format_message << "val1: " << val1 << "\n"
                          << "val2: " << val2 << "\n";

// str member obtains the string associated with a stringstream
istringstream input_istring(format_message.str());
string dump; // place to dump the labels from the formatted message
// extracts the stored ascii values, converting back to arithmetic types
input_istring >> dump >> val1 >> dump >> val2;
cout << val1 << " " << val2 << endl; // prints 512 1024