Programming Fundamentals lecture-22.pptx

Programming Fundamentals lecture-22.pptx

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  1 Programming Fundamentals LECTURE-22 GHULAM ABBAS abbas.sbcws@gmail.com
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  2 In the PreviousLecture  TYPES OF DATA FILES  FILE MODES
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  3 Today’s Lecture TEXT FILEFUNCTIONS Stream state member functions File Pointer
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  File mode:File OpenMode #include <fstream> using namespace std; int main() { ofstream outFile("file1.txt", ios::out); outFile << "create a new file and will write this text!n"; outFile.close(); return 0; } If you want to set more than one open mode, just use the OR operator- |. This way: ios::ate | ios::binary
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  TEXT FILE FUNCTIONS Reading/writing a single character from/to file :  get() – read a single character from text file and store in a buffer. e.g file.get(ch);  put() - writing a single character in text file. e.g. file.put(ch);  Reading/writing a line from/to file:  getline() - read a line of text from text file stored in a buffer. e.g file.getline(s,80,”n”);  <<(insertion operator) – write a line to a file. fin<<s;  Reading/writing a word from/to file:  char ch[20];  fin.getline(ch,20, ‘ ‘);  We can use file>>ch for reading and file<<ch writing a word in text file.  The>> operator does not accept white spaces so it will stop when it encounters a space after word and stores that word in ch.
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  A PROGRAM TOCREATE A TEXT FILE #include<iostream> #include<fstream> using namespace std; main() { ofstream fout("abc.txt"); fout<<"i am creating a new text filen"; fout<<"this text file contains alphabets and numbersn"; fout<<"Ghulam Abbasn"; fout.close(); } The above program will create a text file “abc.txt” and store two lines in it. You can store as many lines as you want.
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  A PROGRAM TOREAD A TEXT FILE CHRACTER BY CHARACTER The above program will read a text file “abc.txt” one character at a time and display it on the screen. #include<iostream> #include<fstream> using namespace std; main() { ifstream fin("abc.txt"); char ch; while(!fin.eof()) { fin.get(ch); cout<<ch; } fin.close(); }
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  A PROGRAM TOREAD A TEXT FILE WORD BY WORD The above program will read a text file “abc.txt” one word at a time and display it on the screen. #include<iostream> #include<fstream> using namespace std; main() { ifstream fin("abc.txt"); char ch[20]; while(!fin.eof()) { fin>>ch; cout<<ch<<"t"; } fin.close(); }
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  A PROGRAM TOREAD A TEXT FILE LINE BY LINE The above program will read a text file “abc.txt” one line at a time and display it on the screen. #include<iostream> #include<fstream> using namespace std; main() { ifstream fin("abc.txt"); char ch[80]; while(!fin.eof()) { fin.getline(ch,80); cout<<ch<<endl; } fin.close(); }
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  Stream state memberfunctions  In C++, file stream classes inherit a stream state member from the ios class, which gives out the information regarding the status of the stream.  Example eof() –used to check the end of file character fail()- used to check the status of file at opening for I/O bad()- used to check whether invalid file operations or unrecoverable error . good()- used to check whether the previous file operation has been successful
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  File Pointer  InputPointer (get pointer)  The input pointer is used for reading contents of a given file location.  Output Pointer (put pointer)  The output pointer is used for writing to a given file location.  We can use these pointers to move through the files while reading or writing.  The input pointer is used for reading the contents of a given file location and  The output pointer is used for writing to a given file location.
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  File Pointer –Default Actions  When a file opened in read-only mode, the input pointer is automatically set at the beginning of the file.  When a file is opened in write-only mode, the existing contents are deleted and the output pointer is set at the beginning.  When a file is opened in append mode, the output pointer moves to the end of file.
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  Functions for Manipulationsof File Pointers  seekg( Moves get pointer (input) to a specified location.  seekp( ) Moves put pointer(output) to a specified location.  tellg( ) Gives the current position of the get pointer.  tellp( ) Gives the current position of the put pointer.
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  Seek Function withAbsolute Position  infile.seekg(10);  Moves the file pointer to the byte number 10.  The bytes in a file are numbered beginning from zero. Therefore, the pointer pointing to the 11th byte in the file.
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  Seek Function withSpecifying the Offset  seekg( offset, refposition);  seekp( offset, refposition);  The parameter offset represents the number of bytes the file pointer is to be moved from the location specified by the parameter refposition.  The refposition takes one of the following three constants defined in the ios class:  ios : : beg start of the file  ios : : cur current position of the pointer  ios : : end end of the file
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  Example: Seek Functionwith Specifying the Offset fout.seekg(0, ios : : beg); Go to start fout.seekg(0, ios : : cur); Stay at the current position fout.seekg(0, ios : : end); Go to the end of file fout.seekg(m, ios : : beg); Move to (m+1)th byte in the file fout.seekg(m, ios : : cur); Go forward by m bytes from the current position fout.seekg(-m, ios : : cur); Go backward by m bytes from the current position fout.seekg(-m, ios : : end) Go backward by m bytes from the end
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  Example: Seek Functionwith Specifying the Offset #include <fstream> #include <string.h > using namespace std; int main() { char str[80]; cout<<"enter a string "; cin>>str; int len=strlen(str); fstream fs; fs.open("abc.txt", ios::in | ios::out); for(int i=0; i<len;i++) { fs.put(str[i]); } fs.seekg(20,ios::beg); char ch; while(fs) { fs.get(ch); cout<<ch; } return 0; }
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  Example: Seek Functionwith Specifying the Offset #include <iostream> #include <fstream> #include<iomanip>//for setw using namespace std; int main() { ofstream out_stream; double d1, d2; char file_name[20]; // cstring cout << "Enter output file name: "; cin >> file_name; out_stream.open(file_name); if (out_stream.fail()) { cout << "Output file could not be opened.n"; exit(1); } out_stream.setf(ios::fixed); //out_stream.setf(ios::showpoint); cout << "Enter two numbers: "; cin >> d1 >> d2; out_stream << setprecision(3) << setw(10) << d1 << setw(10) << d1 * d1 << endl; out_stream << setprecision(3) << setw(10) << d2 <<setw (10) << d2 * d2 << endl; out_stream.close(); }