list1717.cpp

teach yourself C++ in 21 days 第五版

//Listing 17.17 Appending to the End of a File
#include <fstream>
#include <iostream>
using namespace std;

int main()   // returns 1 on error
{
   char fileName[80];
   char buffer[255];
   cout << "Please reenter the file name: ";
   cin >> fileName;

   ifstream fin(fileName);
   if (fin)                // already exists?
   {
      cout << "Current file contents:\n";
      char ch;
      while (fin.get(ch))
         cout << ch;
      cout << "\n***End of file contents.***\n";
   }
   fin.close();

   cout << "\nOpening " << fileName << " in append mode...\n";

   ofstream fout(fileName,ios::app);
   if (!fout)
   {
      cout << "Unable to open " << fileName << " for appending.\n";
      return(1);
   }

   cout << "\nEnter text for the file: ";
   cin.ignore(1,'\n');
   cin.getline(buffer,255);
   fout << buffer << "\n";
   fout.close();

   fin.open(fileName);  // reassign existing fin object!
   if (!fin)
   {
      cout << "Unable to open " << fileName << " for reading.\n";
      return(1);
   }
   cout << "\nHere's the contents of the file:\n";
   char ch;
   while (fin.get(ch))
      cout << ch;
   cout << "\n***End of file contents.***\n";
   fin.close();
   return 0;
}