C + + Primer plus random.cpp

1 //Random.cpp--random access to a binary file2#include <iostream>//Not required by most systems3#include <fstream>4#include <iomanip>5#include <cstdlib>//(or Stdlib.h) for exit ()6 Const intLIM = -;7 structPlanet8 {9     CharName[lim];//Name of PlanetTen     DoublePopulation//Its population One     DoubleG//Its acceleration of gravity A }; -  - Const Char* File ="Planet.dat";//assumed to EXIST (binary.cpp example) theInlinevoidEatline () { while(Std::cin.Get() !='\ n')Continue; }//inline function, where the code is replaced at the time of compilation -                                                                         //to solve the efficiency problem of function calls -  - intMain () + { -     using namespaceStd//using the standard library namespace in the main function + Planet Pl; Acout <<fixed;//Digital fixed-point form output at  - //Show Initial contents -FStream finout;//Create a file stream, named Finout - finout.open (file, -Ios_base::inch| Ios_base:: out| Ios_base::binary);/*Call Finout Sub-function open,ios_base::in, ios_base::out use input and output, I - os_base::binary indicates binary operation of file data*/ in     //note:some Unix systems require omitting | ios::binary -     intCT =0; to     if(Finout.is_open ())//Finout.is_open () returns an integer indicating whether the open file was successful +     { -FINOUT.SEEKG (0);//Position the file pointer to the location of the file 0 (first character), FILENAM.SEEKG (Num); thecout <<"Here is the current contents of the" *<< file <<"file:\n";  $ Panax Notoginseng         /*Finout.read Read the file and convert the character output (originally binary) - Filename.read ((type*) &struct,sizeof)*/ the          while(Finout.read (Char*) &AMP;PL,sizeofPL))  +         { Acout << ct++ <<": "<< SETW (LIM) << pl.name <<": " the<< Setprecision (0) << SETW ( A) <<pl.population +<< Setprecision (2) << SETW (6) << PL.G <<Endl; -         } $         if(Finout.eof ())//reach end of File clear error message $Finout.clear ();//Clear EOF Flag -         Else -         { theCerr <<"Error in Reading"<< file <<". \ n"; - exit (exit_failure);Wuyi         } the     } -     Else Wu     { -Cerr << File <<"could not being opened--bye.\n"; About exit (exit_failure); $     } -  - //Change a record -cout <<"Enter The record number you wish to change:"; A     LongRec; +CIN >>Rec; theEatline ();//the input before the wrap is used to enter characters or the next time a character is entered -     if(Rec <0|| Rec >=CT) $     { theCerr <<"Invalid Record number--bye\n"; the exit (exit_failure); the     } theStreampos Place = Rec *sizeofPl//the data type of the file pointer location place = rec * sizeof PL will place point to a fixed position -FINOUT.SEEKG (place);//Random Access in     if(Finout.fail ()) the     { theCerr <<"Error on attempted seek\n"; About exit (exit_failure); the     } the  theFinout.read ((Char*) &AMP;PL,sizeofPL);//to open the file before exporting +cout <<"Your selection:\n"; -cout << Rec <<": "<< SETW (LIM) << pl.name <<": " the<< Setprecision (0) << SETW ( A) <<pl.populationBayi<< Setprecision (2) << SETW (6) << PL.G <<Endl; the     if(finout.eof ()) theFinout.clear ();//Clear EOF Flag -  -cout <<"Enter Planet Name:"; theCin.Get(Pl.name, LIM);//read-in characters: Cin.get (name,sizeof (Type)) the eatline (); thecout <<"Enter Planetary Population:"; theCIN >>pl.population; - eatline (); thecout <<"Enter Planet ' s acceleration of gravity:"; theCIN >>PL.G; theFINOUT.SEEKP (place);//the pointer changes after the file is manipulated to reposition the pointer94Finout.write ((Char*) &AMP;PL,sizeofPL) << flush;//prevent program interruption too late to send out data <<flush the     if(Finout.fail ()) the     { theCerr <<"Error on attempted write\n";98 exit (exit_failure); About     } - 101 //Show revised file102CT =0;103FINOUT.SEEKG (0);//then output everything, position the pointer with the start position104cout <<"Here is the new contents of the"<<file the<<"file:\n";106      while(Finout.read (Char*) &AMP;PL,sizeofPL))107     {108cout << ct++ <<": "<< SETW (LIM) << pl.name <<": "109<< Setprecision (0) << SETW ( A) <<pl.population the<< Setprecision (2) << SETW (6) << PL.G <<Endl;111     } theFinout.close ();//Close File113cout <<"done.\n"; the //Keeping Output Window open the     //cin.clear (); the     //eatline ();117     //cin.get ();118     return 0;119}

C + + Primer plus random.cpp