1. File streams Chapter 14.2-14.6, 12.1-12.4, 12.6-12.8

2. Remember redirection?  It lets you read from a file prompt> a.out outfile  We have substituted the disk file infile for the standard input file (keyboard)  and outfile for the standard output file (display)

3. Redirection isn't enough What if we wanted to read from more than one file at the same time? student registration file prepare bill -> tuition bill student info file

4. File Streams Its really not much different than using cin and cout. Why call it a STREAM? All devices can be viewed simply as a stream of chars (like a river is a stream of water) whether it is an input or output stream.

5. How to use file streams 1. Include 2. Declare input files as ifstream 3. Declare output files as ofstream 4. To read in, use >> 5. To write out use << 6. Keep going until eof is reached

6. #include int main() { const char * filename="/home/faculty2/lambert/Public/unixdict.txt"; string word; ifstream wordfile(filename); if (!wordfile) // check to see if file is there. {cout << "Error: no file name " << filename << endl; return EXIT_SUCCESS; }

7. int count=0; while (wordfile >> word) // keep going until eof. { cout << "Word is " << word << endl; count++; } wordfile.close(); cout << "the number of words in the file is " << count << endl; return EXIT_SUCCESS; }

8. Using an output file The same as modifications to input; instead of cout, use filename make sure you format check for problems opening (file will be erased if there)

9. Passing file streams as parameters Always pass as reference type is ifstream or ofstream void getnextword(ifstream&, string&); getnextword(infile, word); void getnextword(ifstream &infile, string &word) { if (!infile.eof()) infile >> word; }

10. Write your own Write a program that reads word from a file, writes them to a duplicate file, and counts the number of words. Use a function, writeword, which has two parameters, the file to be written to and the word being written (an input parameter)

11. More stream functions open, get, put, eof, fail, close put and get are used for reading files a char at a time THEY DO NOT SKIP SPACES etc! You can use cin type input ( >> ) but it skips white space. Remember how cin does the same?

12. cerr, section 12.2.3 What if you wanted to output an error but the person was redirecting the output to a file? prompt> a.out >outfile YOU WOULDN'T SEE THE ERROR! the cerr stream is a special kind of output which would NOT be redirected to the standard output device.

13. cerr Original program that read in words and printed them to the screen could redirect output and produce the same results as second. But if you want to see errors no matter what, use cerr: if (!wordfile) // check to see if file is there. { cerr << "Error: no file name " << filename << endl; return EXIT_SUCCESS; }

14. Output manipulators a function called as though it were being output, e.g., endl setw, precision, showpoint, scientific, fixed can be used on any output stream, cout or file some defined in iostream; some in iomanip (those with parameters) problems with some on our compiler. use flags

15. Output Manipulators { float x; cout << setw(10) << x << endl; } endl we've seen setw(10) minimum of 10 spaces (x, like all output is right justified) (both work fine on our system)

16. Output flags instead of: float x; cout << fixed << precision(2) << x << endl; use: cout.setf (ios::fixed); cout.precision(2); cout << "x" << endl; should do the same thing, but the first creates a syntax error on our compiler

17. Output flags/manipulators Lots of them: right, left, internal fill, setfill hex, octal, dec, showbase uppercase scientific, fixed, showpoint precision showpos I will not expect you to memorize these for a test; know they exist so you can look them up as needed

18. Input functions (get) get (can use with cin or any input stream) cin.get(ch); // puts char in output parameter ch = cin.get() // returns the char as function value cin.get(chararray, maxsize, ) // null character inserted into array as terminator // null character remains in input stream // works like getline

19. Input functions getline (with cin or any input stream) null character inserted in array at end delimiter read and discarded (UNLIKE get) cin.getline(chararray, size, ) member of istream class getline(istream, string, ) string is of string class. NO dot notation

20. More input functions ignore istream.ignore(); // skips over one char istream.ignore(n); // skips over n chars istream.ignore(n, '?'); // skips over n chars, or until a question mark whichever is first' examples: cin.ignore(); ifstream ins; ins.ignore(1000, '\n'); // throw away next return