1. Interactive I/O Input from keyboard Must prompt user User friendly
echo checking
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2. Noninteractive processing
Batch processing
Store values in a file
File input and Output
C++ can write and read from files just as to keyboard and screen
standard input file - keyboard
standard output file - screen or printer
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3. Advantages to noninteractive
can edit data, prepare ahead of time
Can rerun file without reentering data
Can examine output at leisure
Can display output to screen or print
Can use out as input into another program
means of communicating between programs
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4. files
file - named secondary memory area that holds a collection of information
usually stored on an auxiliary storage device
examples
external file - a file that is used to communicate with people or programs. It is stored externally to the program.
internal file - a file that is created but not saved
(scratch file)
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5. text files composed of characters only Differs from .doc(x) file
Size of file
Can be created in notepad, Visual C
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6. File organization
naming rules(dos) - 1 to 8 character name, optionally followed by a period and up to a 3 character extension (recommended for programmers!)
extension tells the type of file
 .cpp – c++ program file
.doc – Word file
.exe – executable file
.obj - Compiled programs - object files
.txt - Text files(ASCII form, printable)
.dat - data files
file is composed of tracks, sectors
FAT table
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7. files program files - contains program instructions
data files - contains data, collection of records
record - one entity
i.e. customer file - each record holds data for each customer
 fields - data element
 customer file has name field, account field,...
record key or key field
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8. Path Filename includes path No path – default ddirectory
c:\temp\junk.txt
Temp directory is usually accessible to students
\ is a special character inside strings
c:\\temp\\junk.txt
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9. Buffer File i/o is slow Buffer is temporary storage area
data for input or output gets written to buffer
i/o happens when buffer is full
Less reading and writing transaction
Happens behind the scenes
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10. Writing Data to a File 1. Open the file as an output file.
2. Write the elements.
3. Close the file (happens automatically when you exit the program)
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11. Example in c++
#include <fstream> //includes ifstream and ofstream //declare a handle ofstream outFile; //output only (writing) //open the file outFile.open("c:\\temp\\stuff.txt"); //outfile is associated with stuff // write to file outFile << "Hello" << endl;
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12. Opening for output causes:
ofstream outFile;//any variable can be used here
outFile.open(filename); //include path
The directory is searched for "filename".
If it doesn't exist, it is created.
If it does exist, it will be written over
The file is set to write mode.
A buffer is created.
A file pointer is set to the beginning of file. This is updated with each write.
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13. Reading the Data: Open the file for input. Read the data
Close the file. 
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14. Opening for input causes:
The directory is searched for "filename". The file is set to read mode.
A buffer is created in memory.
A file pointer is set to the beginning of file.
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15. Example in c++
#include <fstream> //declare a handle ifstream inFile; //input only (reading) //open the file inFile.open("c:\\temp\\stuff.txt"); //DON"T FORGET TO CHECK IF IT WORKED!!! inFile >> name >> age;
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16. Using Files in c++: 1. #include <fstream>
2.declare file streams ifstream inFile; //input only (reading) ofstream outFile; //output only (writing)
3. open each file for reading or writing filevar.open(filename)
4.specify names of file streams in input and output statement
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17. Open Files
inMPG.open("inmpg.dat"); outMPG.open("outmpg.dat"); 1. associates a stream variable with file 2. output file –
check if it exists, overwrite, if not create sets marker to beginning of file
good idea to open all files at the beginning
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18. input and output-
use var name in input and output statements in place of cin and cout inFile >> startMiles >> endMiles;
outFile << "the mileage per gallon is " << mpg << endl;
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19. Input Failure invalid data -> fail state
after fail state, any further i/o operations have no effect
opening file that doesn't exist -> fail state
Important to test for this!!!!!!
inMPG.open("inmpg.dat");
if(!inMPG) {
cout << “Can’t open inmpg.dat”;
return -1; }
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