TEXT FILES

CIN / COUT REVIEW  We are able to read data from the same line or multiple lines during successive calls.  Remember that the extraction operator (>>) skips any leading white space (spaces, tabs, newlines) characters before reading the data. User Input 45 67\n 3 8\n int num1, num2, num3, num4; cin >> num1; cin >> num2; cin >> num3; cin >> num4; num1 = 45 num2 = 67 num3 = 3 num4 = 8

CIN / COUT REVIEW  If you want to skip past ALL remaining data (not just white space) on a line and go to the next line, you can use cin.ignore(). User Input 45 67\n 3 8\n int num1, num2; cin >> num1; cin.ignore(100, ‘\n’); cin >> num2; num1 = 45 skips remaining data on line 1 num2 = 2

CIN / COUT REVIEW  If you want to read all characters (includig whitespace characters instead of skipping past them) you can use the cin.get() to read into char type variables. User Input 4\n 3 8\n char ch1, ch2, ch3, ch4, ch5; cin.get(ch1); cin.get(ch2); cin.get(ch3); cin.get(ch4); cin.get(ch5); ch1 = ‘4’ ch2 = ‘\n’ ch3 = ‘3’ ch4 = ‘ ‘ ch5 = ‘8’

CIN / COUT REVIW  To display output to the screen we used “cout”.  The cursor remains where the last output occurs unless “endl” or “\n” is added ( this allows more output to be added to same line). CODE cout << “Hello”; cout << “Hello” << endl; cout << “Good”; cout << “bye” OUTPUT Hello_ Hello _ Goodbye_

CIN / COUT REVIEW  Output can be formatted using manipulators:  fixedforces floating point number to be displayed in a decimal format (instead of scientific)  setw()sets the display with of output data  setprecision()sets number of decimal places to be displayed int num = 456; float val = ; cout << fixed << showpoint << setprecision(2); cout << val; cout << setprecision(1) << val; cout << setw(4) << val; cout << setw(1) << num; cout << setw(5) << num; OUTPUT _ __456

CIN / COUT REVIEW  “cin” will read data according to the data type of input variable  Reading strings stops at the first whitespace character  Using “getline()” forces all characters on line to be read Input data: “\n” int num; float value; char ch; string words cin >> value >> ch; cin >> ch >> num; cin >> words >> num >> value; getline(cin, words); cin >> ch >> ch >> value >> words; value = 435.0, ch = ‘8’ ch = ‘4’, num = 35 words = “435”, num = 8, value = 0.8 words = “ ” ch = ‘3”, value = 5.0, words = “8.8”

TEXT FILES  Text File  File Of ASCII Characters  Can Be Viewed In Text Editor  Last Character On Line Is “newline” Character (‘/n’)  Last Character In The File Is “eof” Character  Can Be Created With Any Text Editor (notepad, compiler…)  Input File Stream  Stream Of Data  Same As Keyboard Input But From The File  Input File Stream Can Be Tricky

TEXT FILES  File Examples character (or string) Data : This Is A Test. This Is Only A Test.(‘/n’) Now Is The Time For All Good Men(‘/n) To Come To The Aid Of Their Country.(‘/n’) (eof) Mixed Data: Smith Joe (‘/n) Able Sam (‘/n) Blow Joe (eof)

USING TEXT FILES  Five Steps For File Access  # 1 – Add “#include ” To Top Of Program  Adds Library For File Access  # 2 – Declare File Stream Variable  Use Valid Identifier Name  Separate File Stream Variables are Required For Text Files Which are Dependant On the Mode (“read” or “write”) –For Input Stream ifstream Identifier - example: ifstream inData; –For Output Stream ofstream Identifier - example:ofstream outData;

USING TEXT FILES  Five Steps For File Access (cont.)  #3 – Open The File Stream  Use The “open” Function file-stream-variable.open(physical file name) example:inData.open(“c:\test.txt); example:const string FILENAME = “test.txt”; outData.open(FILENAME.c_str()); Note:You may need to list all backslashes as double backslashes in file names (e.g. “c:\\study.txt”). Note:file-stream-variable must be of type ifstream or ofstream physical filenames can be a literal string or a C string variable (must append “.c_str()” onto the variable name to convert it to a C string – and be sure to include the “string” header file).

USING TEXT FILES  Five Steps For File Access (cont.)  Potential File “Path” Issues  Opening Input File Stream (read only)  Checks For File Existence If Exists File Opened, Read Pointer Placed At Beginning and File Stream In Non-Error State If MissingFile Stream Is Put Into Error State  Opening Output File Stream (write only)  Checks For File Existence If ExistsFile Opened, All Data Erased, File Ready For Data If MissingNew File Opened, File Ready For Data Note – Text Files Can Only Be Open In One Mode At A Time (Read or Write)

USING TEXT FILES  Five Steps For File Access (cont.)  File Stream Status Can Be Used For Error Checking After opening file “figures.txt” for reading, use the file stream variable to check the results. inData.open("figures.txt"); if ( !inData ) cout << "Error opening file!" << endl; else { // continue program } Result:Error message is issued if program was not able to open file figures.txt.

USING TEXT FILES  Five Steps For File Access (cont.)  #4 – Read Or Write Data File  Similar To Standard Input/Output Process  Instead Of Using “cin” Use File Stream Variable –File “study.txt” contains: (‘\n’) (‘\n’) –Code:double num1; int num2; ifstream inData; ofstream outData; inData >> num1;\\Reads First Number inData >> num2;\\Reads Second Number results:num1 = 35.75, num2 = 47

USING TEXT FILES  Five Steps For File Access (cont.)  Instead Of Using “cout” Use File Stream Variable  Use Of “manipulators” For Formatting Data Has The Same Affect On Output File As They Do With Displayed Output (..setprecision(), setw()…etc) double num1, num2; –Code:num1 = ; num2 = num1 * 2; ( ) outData << fixed << showpoint << setprecision(2); outData << setw(6) << num1 << ‘ ‘ << set(6) << num2 << endl; –Result:_53.76 _106.32(\n’)

USING TEXT FILES  Five Steps For File Access (cont.)  #5 – Close The Open File When Finished  As Soon As File Access Is Completed, Files Should Be Closed inData.close(); outData.close();  Leaving Files Open When Not Needed Increases Opportunity Of Corrupted Files

Using Text Files  Five Steps  Include “fstream” Header File At Top Of Program  Declare File Stream Variables (ifstream or ofstream)  Open The Data File  Use File Stream Variable To Access File (not cin/cout)  Close Any Open Files When Finished With File  Passing The File Stream To A User Defined Function Must Always Be Passed By Reference syntax  For example: void readFile(ifstream& inData) (function header) void readFile(ifstream& inData); (prototype)