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2010-05-25T14:21:06Z

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2010-05-25T10:24:01Z

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==Accessing Data in a File==

<source lang="cpp">
#include <algorithm>
#include <cstdlib>
#include <fstream>
#include <functional>
#include <iostream>
#include <iterator>
#include <vector>
using namespace std;
template <class T>
void print(T& c){
for( typename T::iterator i = c.begin(); i != c.end(); i++ ){
std::cout << *i << endl;
}
}
int main(){
vector<int> output_data( 10 );
generate( output_data.begin(), output_data.end(), rand );
transform( output_data.begin(), output_data.end(),output_data.begin(), bind2nd( modulus<int>(), 10 ) );
ofstream out( "data.txt" );
if( !out )
{
cout << "Couldn"t open output file\n";
return 0;
}
copy( output_data.begin(), output_data.end(),ostream_iterator<int>( out, "\n" ) );
out.close();
ifstream in( "data.txt" );
if( !in )
{
cout << "Couldn"t open input file\n";
return 0;
}
vector<int> input_data( (istream_iterator<int>( in )),istream_iterator<int>() );
in.close();
print( output_data );
print( input_data );
}

</source>

==basic file operations==

<source lang="cpp">
#include <iostream>
#include <fstream>
using namespace std;
int main () {
ofstream myfile;
myfile.open ("example.txt");
myfile << "Writing this to a file.\n";
myfile.close();
return 0;
}

</source>

==basic file operations: open and save==

<source lang="cpp">
#include <iostream>
#include <fstream>
using namespace std;
int main () {
ofstream myfile;
myfile.open ("example.txt");
myfile << "Writing this to a file.\n";
myfile.close();
return 0;
}

</source>

==Connect ofstream and streambuf and operations with streambufs.==

<source lang="cpp">
#include <iostream>
#include <fstream>
using namespace std;
int main(void){
int c;
char *filename = "test.txt";
ofstream outfile;
streambuf *out, *input = cin.rdbuf();
outfile.open( filename, ios::ate | ios::app);
if (!outfile)
{
cerr << "Could not open " << filename;
return(-1);
}
out = outfile.rdbuf();
while ( (c = input -> sbumpc() ) != EOF){
cout << char(c); // Echo to screen.
if (out -> sputc(c) == EOF)
cerr << "Output error";
}
}

</source>

==eat the newline after the file name==

<source lang="cpp">
#include <iostream>
#include <fstream>
using namespace std;
int main()
{
char buffer[255];
ofstream fout("text.txt");
fout << "This line written directly to the file...\n";
cout << "Enter text for the file: ";
cin.ignore(1,"\n");
cin.getline(buffer,255);
fout << buffer << "\n";
fout.close();
ifstream fin("text.txt");
char ch;
while (fin.get(ch))
cout << ch;
fin.close();
return 0;
}

</source>

==ofstream.fail() Demo==

<source lang="cpp">
#include <fstream>
#include <iostream>
using namespace std;
int main ()
{
ofstream outfile;
outfile.open("file.dat");
cout << "( outfile) = " << outfile << endl;
cout << "( outfile.fail()) = " << outfile.fail() << endl;
return 0;
}

</source>

==ofstream: Use read(), write(), ios::out | ios::binary==

<source lang="cpp">
#include <iostream>
#include <fstream>
using namespace std;

int main()
{
int n[5] = {1, 2, 3, 4, 5};
register int i;

ofstream out("test", ios::out | ios::binary);
if(!out) {
cout << "Cannot open file.\n";
return 1;
}

out.write((char *) &n, sizeof n);

out.close();

for(i = 0; i <5; i++) // clear array
n[i] = 0;

ifstream in("test", ios::in | ios::binary);
if(!in) {
cout << "Cannot open file.\n";
return 1;
}

in.read((char *) &n, sizeof n);

for(i = 0; i <5; i++) // show values read from file
cout << n[i] << " ";

in.close();

return 0;
}

</source>

==Output file with ofstream==

<source lang="cpp">
#include <iostream>
#include <fstream>
using namespace std;
int main()
{
ofstream pout("test");
if(!pout) {
cout << "Cannot open file.\n";
return 1;
}
pout << "A 444 555-4444\n";
pout << "B 222 555-2222\n";
pout << "Joe 333 555-1111\n";
pout.close();
return 0;
}

</source>

==put( ) to write all characters from zero to 255 to a file called CHARS.==

<source lang="cpp">
#include <iostream>
#include <fstream>
using namespace std;

int main()
{
int i;
ofstream out("CHARS", ios::out | ios::binary);

if(!out) {
cout << "Cannot open output file.\n";
return 1;
}

// write all characters to disk
for(i=0; i<256; i++) out.put((char) i);

out.close();
return 0;
}

</source>

==reads strings entered at the keyboard and writes them to disk==

<source lang="cpp">
#include <iostream>
#include <fstream>
using namespace std;

int main(int argc, char *argv[])
{
if(argc!=2) {
cout << "Usage: output <filename>\n";
return 1;
}

ofstream out(argv[1]); // output, normal file

if(!out) {
cout << "Cannot open output file.\n";
return 1;
}

char str[80];
cout << "Write strings to disk. Enter ! to stop.\n";

do {
cout << ": ";
cin >> str;
out << str << endl;
} while (*str != "!");

out.close();
return 0;
}

</source>

==Setting the locale to German_Germany==

<source lang="cpp">
#include <iostream>
#include <fstream>
#include <locale>
using namespace std;
int main()
{
ofstream fout("test.dat");
if(!fout) {
cout << "Cannot open file.\n";
return 1;
}
cout << "The original locale is " << fout.getloc().name();
locale loc("German_Germany");
fout.imbue(loc);
cout << "The current locale is now " << fout.getloc().name();
cout << endl;
if(has_facet<moneypunct<char, true> >(fout.getloc())) {
const moneypunct<char, true> &mp = use_facet<moneypunct<char, true> >(fout.getloc());
cout << "Money symbol: " << mp.curr_symbol() << endl;
cout << "Thousands separator: " << mp.thousands_sep() << endl;
}
fout.close();
if(!fout.good()) {
cout << "Error closing file.\n";
return 1;
}
return 0;
}

</source>

==Uses put() to write all characters from zero to 255 to a file==

<source lang="cpp">
#include <iostream>
#include <fstream>
using namespace std;
int main()
{
int i;
ofstream out("CHARS_File", ios::out | ios::binary);
if(!out) {
cout << "Cannot open output file.\n";
return 1;
}
// write all characters to disk
for(i=0; i<256; i++)
out.put((char) i);
out.close();
return 0;
}

</source>

==writes formatted output to a file, using ==

<source lang="cpp">
#include <fstream>
#include <iostream>
#include <string>
using namespace std;

int main(){
char ch = "x";
int j = 77;
double d = 6.02;
string str1 = "test";
string str2 = "this is a test";

ofstream outfile("fdata.txt");

outfile << ch
<< j
<< " "
<< d
<< str1
<< " "
<< str2;
cout << "File written\n";
return 0;
}

</source>

==Writes information inputted to a file==

<source lang="cpp">
#include <fstream>
#include <iostream>
using namespace std;
int main ()
{
char data[80];
ofstream outfile;
outfile.open("file.txt");
cout << "Writing to the file" << endl;
cout << "Enter your name: ";
cin.getline(data, 80);
outfile << data << endl;
cout << "Enter your id number: ";
cin >> data;
cin.ignore();
outfile << data << endl;
outfile.close();
return 0;
}

</source>

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