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TEXT FILES

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 (&gt;&gt;) skips any leading white space (spaces, tabs, newlines) characters before reading the data. User Input 45 67<br> 3 8<br>.

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TEXT FILES

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  1. TEXT FILES

  2. 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

  3. 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 num1 = 45 skips remaining data on line 1 num2 = 2 int num1, num2; cin >> num1; cin.ignore(100, ‘\n’); cin >> num2;

  4. 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’

  5. 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_

  6. CIN / COUT REVIEW • Output can be formatted using manipulators: • fixed forces 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 = 4.8728; cout << fixed << showpoint << setprecision(2); cout << val; cout << setprecision(1) << val; cout << setw(4) << val; cout << setw(1) << num; cout << setw(5) << num; OUTPUT 4.87 4.9 _4.9 456 __456

  7. 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: 435 8.8“\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 = “435 8.8” ch = ‘3”, value = 5.0, words = “8.8”

  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

  9. 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 111-11-1111 3.85(‘/n) Able Sam 222-22-2222 3.25(‘/n) Blow Joe 333-33-3333 2.50(eof)

  10. USING TEXT FILES • Five Steps For File Access • # 1 – Add “#include <fstream>” 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;

  11. 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).

  12. 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 Missing File Stream Is Put Into Error State • Opening Output File Stream (write only) • Checks For File Existence If Exists File Opened, All Data Erased, File Ready For Data If Missing New File Opened, File Ready For Data Note – Text Files Can Only Be Open In One Mode At A Time (Read or Write)

  13. 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.

  14. 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: 35.75 47(‘\n’) 36.50 54(‘\n’) <eof> • 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

  15. 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 = 53.75875; num2 = num1 * 2; (106.3175) outData << fixed << showpoint << setprecision(2); outData << setw(6) << num1 << ‘ ‘ << set(6) << num2 << endl; • Result: _53.76 _106.32(\n’) <eof>

  16. 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

  17. 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)

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