Software Layers 2 Introduction to unix 2

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Program Input/Output

Week 5
4 kinds of Program I/O:

standard I/O: cin (keyboard), cout (monitor)
I/O redirection: unix operators <, >>, | (files)
command-line: using arguments in your C++ programs
file I/O: using files in your C++ programs

IO redirection:

You can redirect standard I/O from the unix prompt

cmd > filename  sends all output from the cmd to specified file (file is overwritten)

eg: myProgram > results.txt

cmd >> filename  results of the cmd are appended to file's current contents (file isn't overwritten)

eg: myProgram >> all_results.txt

cmd < filename  the cmd uses the data in the file instead of standard input

eg: myProgram < data.txt

cmd1 | cmd2  the results of cmd1 are used as the input to cmd2

eg: cat results.txt | wc

eg:

% cat data.txt

The answer to life, the universe, everything is 42.

QED.

% wc data.txt

4 10 59 data.txt

% cat data.txt | wc

4 10 59

C++ Command line Parameters:

The main function can contain two special formal parameters:

int argc  the number of cmd line arguments (including the program name, so argc >= 1)

char** argv  an array of strings for each argument

eg:

#include
int main(int argc, char** argv) {
cout << "argc is " << argc << endl;

for (int index=0; index < argc; index++) {

cout << "argv[" << index << "] is "

<< argv[index] << endl;

}

return 0;

}

note: because argv contains strings, you may need to do string conversions (using the routines like atof and atoi from stdlib.h)

C++ Files

Week 5

Introduction

Why have files  long term storage & retrieval of information
I/O streams:

stream = a communication mechanism for data transfer between a device and a program
input stream = data from a sender device (keyboard)
output stream = a way to send data to a receiver device (monitor)
streams can also be bi-directional, and random-access (however, we only consider either input or output streams, and not random-access)

Devices:

streams must be associated with a physical device (such as a text file on a floppy disk)

Stream ADT operations:

Open
Get data from an input stream
Detect end of input stream
Put data on an output stream

Stream ADT is implemented by various C++ classes

Streams

Standard I/O streams are defined in iostream.h
File streams are defined in fstream.h  this contains the classes: ofstream & ifstream.

Code:

Instance.open(FileName)  opens/renews file if possible.
Instance.close()  closes file (good programming)
Instance.fail()  determines if the operation has failed.

Instance.eof()  detects end of file (useful when looping through input)
Instance.get(VarChar)  reads next char into VarChar
Instance.getline(VarString,MaxLength)  reads next whole line (up to MaxLength) into VarString
OutputStreamInstance.put(VarChar)  writes single char to file
Instance << VarSting << endl;  this code writes VarString into file

eg:

int main(void) {

ifstream InputFile;

ofstream OutputFile;
if (OpenInputFile(InputFile) && OpenOutputFile(OutputFile)) {

CopyIntegers(InputFile, OutputFile);

InputFile.close();

OutputFile.close();

}

else

cout << "Error opening file" << endl;

return(0);

}

//----------------------------------------

CopyIntegers(ifstream &InputFile, ofstream &OutputFile) {

int Data;

InputFile >> Data;

while (!InputFile.eof())

{

OutputFile << Data << " ";

InputFile >> Data;

}

//----------------------------------------

boolean OpenInputFile(ifstream &InputFile) {

string InputFileName;

cout << "Enter the input file name: ";

cin >> InputFileName;
InputFile.open(InputFileName);

return(!InputFile.fail());

}

//----------------------------------------

boolean OpenOutputFile(ofstream &OutputFile) {

string OutputFileName;

cout << "Enter the output file name: ";

cin >> OutputFileName;

OutputFile.open(OutputFileName);

return(!OutputFile.fail());

}

Directory: student
student -> How to Create a Student Recital Program
student -> Tracks, Mixes, Masters, and More!: Analyzing Preservation Priorities for Multitrack Recordings
student -> A chronology 1660-1832 The Restoration Settlement
student -> Introduction
student -> Disaster planning and recovery: post-katrina lessons for mixed media collections
student -> Comparing Hurricanes and Hurricane Seasons
student -> Storm Surge: a rising Danger
student -> Dr. Jeff Masters' WunderBlog
student -> April 9, 2008 Hurricanes (Continued)
student -> Instructions for Writing Hurricane Term Paper

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