The end of chapter 9 concludes with a fairly hefty compilation of some things you have learned thus far. You probably could have simply made a program that grabbed text from a file, but im sure you would still want to associate it with a struct like we have already done. The majority of this program will stay the same as exercise 6 except a couple of additions; one being we create a file stream named “inFile”. We then associate it with a hard-coded file “contrib.txt”, that has our struct info. Then, we check for a file opening error, see if the first line is an integer, and begin grabbing data from the file. This time I use the “new” keyword and make use of the atoi() function to make all this happen. Examine my source to see how I worked through this one:
9. Do Programming Exercise 6, but modify it to get information from a file. The first item
in the file should be the number of contributors, and the rest of the file should consist of
pairs of lines, with the first line of each pair being a contributor’s name and the second
line being a contribution. That is, the file should look like this:
4
Sam Stone
2000
Freida Flass
100500
Tammy Tubbs
5000
Rich Raptor
55000
#include <iostream>
#include <string>
#include <fstream>
#include <cstdlib>
using namespace std;
struct contrib
{
string name;
double amount;
};
int main()
{
// Create input stream
ifstream inFile;
inFile.open("contrib.txt");
// faile-safe
if (!inFile.is_open())
{
cout << "Failed to open: " << inFile << endl;
exit(EXIT_FAILURE);
}
int numDonors = 0;
int patrons = 0;
int grandPatrons = 0;
char lineOne;
cout << "Society for the Preservation of Rightful Influence" << "\n\n";
cout << "Reading File...\n";
(inFile >> lineOne).get();
if(!isdigit(lineOne))
{
cout << "Number of donors not found\n";
return 2;
}
else
cout << "The number of donors is: " << lineOne << "\n\n";
numDonors = atoi(&lineOne);
contrib *society = new contrib[numDonors];
// Gather names and amounts
for(int i = 0; i < numDonors; i++)
{
getline(inFile, society[i].name); // getline to grab names
cout << "Donor # " << (i+1) << " " << society[i].name << endl;
(inFile >> society[i].amount).get();
/*inFile >> society[i].amount;*/
cout << "Amount: " << (i+1) << society[i].amount<< endl;
}
cout << "\n";
// Display donors over 10000
cout << "Grand Patrons: \n";
for(int x = 0; x < numDonors; x++)
{
if(society[x].amount >= 10000)
{
cout << society[x].name << " Donated: "
<< "$ " << society[x].amount << "\n";
grandPatrons = 1;
}
}
if(grandPatrons == 0)
cout << "none\n";
cout << "\n";
// Display all other patrons
cout << "Patrons list: \n";
for(int y = 0; y < numDonors; y++)
{
if(society[y].amount < 10000)
{
cout << society[y].name << " Donated: "
<< "$ " << society[y].amount << "\n";
patrons = 1;
}
}
if(patrons == 0)
cout << "none\n";
delete [] society;
if (inFile.eof())
cout << "End of file reached.\n";
else if (inFile.fail())
cout << "Input terminated by data mismatch.\n";
// free memory
inFile.close();
return 0;
}
Recently I needed to needed to check the endianness of a machine. I assumed the machine was Little Indian but wanted to make sure, thus this C code snippet. It’s important to understand that endian.h is not cross-platform, and exist only on Linux machines. There are standard byte order functions you can use if you are on Windows to figure this stuff out. Perhaps I will show an example of that later.
Demux 