Материал из C\C++ эксперт
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Append to a binary file
#include <iostream>
#include <fstream>
using namespace std;
int main()
{
ofstream outFile("FileWrite.out");
if (outFile.fail()) {
cerr << "Unable to open file for writing." << endl;
exit(1);
}
outFile << "Hello!" << endl;
outFile.close();
ofstream appendFile("FileWrite.out", ios_base::app);
if (appendFile.fail()) {
cerr << "Unable to open file for writing." << endl;
exit(1);
}
appendFile << "Append!" << endl;
appendFile.close();
}Creating a randomly accessed file
#include <iostream>
using std::cerr;
using std::endl;
using std::ios;
#include <fstream>
using std::ofstream;
#include <cstdlib>
using std::exit;
#include <string>
using std::string;
class Account
{
public:
Account( int accountNumberValue, string lastNameValue, string firstNameValue, double balanceValue )
{
setAccountNumber( accountNumberValue );
setLastName( lastNameValue );
setFirstName( firstNameValue );
setBalance( balanceValue );
}
int getAccountNumber() const
{
return accountNumber;
}
void setAccountNumber( int accountNumberValue )
{
accountNumber = accountNumberValue; // should validate
}
string getLastName() const
{
return lastName;
}
void setLastName( string lastNameString )
{
const char *lastNameValue = lastNameString.data();
strncpy( lastName, lastNameValue, 5 );
lastName[ 5 ] = "\0";
}
string getFirstName() const
{
return firstName;
}
void setFirstName( string firstNameString )
{
const char *firstNameValue = firstNameString.data();
strncpy( firstName, firstNameValue, 5 );
firstName[ 5 ] = "\0";
}
double getBalance() const
{
return balance;
}
void setBalance( double balanceValue )
{
balance = balanceValue;
}
private:
int accountNumber;
char lastName[ 15 ];
char firstName[ 10 ];
double balance;
};
int main()
{
ofstream outCredit( "credit.dat", ios::binary );
if ( !outCredit )
{
cerr << "File could not be opened." << endl;
exit( 1 );
}
Account blankClient(1,"AAAAA","BBBBB",1.2);
// output 100 blank records to file
for ( int i = 0; i < 100; i++ )
outCredit.write( reinterpret_cast< const char * >( &blankClient ),
sizeof( Account ) );
return 0;
}Open a binary file
#include <iostream>
#include <fstream>
using namespace std;
int main(int argc, char *argv[])
{
char ch;
ifstream in("test.txt", ios::in | ios::binary);
if(!in) {
cout << "Cannot open file.";
return 1;
}
while(in) { // in will be false when eof is reached
in.get(ch);
if(in) cout << ch;
}
return 0;
}R 9.9
T 9.9
M 4.8
Open a binary file and read
#include <iostream>
#include <fstream>
using namespace std;
int main(int argc, char *argv[]){
char ch;
ifstream in("test.txt", ios::in | ios::binary);
if(!in){
cout << "Cannot open file.";
return 1;
}
while(in){
in.get(ch);
cout << ch;
}
}Output a binary file in hexadecimal
#include <iostream>
#include <fstream>
#include <ctype.h>
#include <iomanip>
#include <stdio.h>
using namespace std;
int main(int argc, char *argv[]){
ifstream in("text.txt", ios::in | ios::binary);
if(!in){
cout << "Cannot open input file." << endl;
exit (1);
}
int i, j;
int count = 0;
char c[16];
cout.setf(ios::uppercase);
while(!in.eof()){
for(i=0; i<16 && !in.eof(); i++)
in.get(c[i]);
if(i<16)
i--;
for(j=0; j < i; j++)
cout << setw(3) << hex << (int) c[j];
for(; j < 16; j++)
cout << " ";
for(j=0; j < i; j++)
if(isprint(c[j]))
cout << c[j];
else
cout << ".";
cout << endl;
count ++;
if(count==16){
count = 0;
cout << "Press ENTER to continue: ";
cin.get();
cout << endl;
}
}
in.close();
}Reading binary file
#include <iostream.h>
#include <fstream.h>
int main () {
char * buffer;
long size;
ifstream file ("example.dat", ios::in|ios::binary|ios::ate);
size = file.tellg();
file.seekg (0, ios::beg);
buffer = new char [size];
file.read (buffer, size);
file.close();
cout << "the complete file is in a buffer";
delete[] buffer;
return 0;
}the complete file is in a buffer"
Unformatted and Binary I/O
#include <iostream>
#include <fstream>
using namespace std;
int main(int argc, char *argv[])
{
char ch;
if(argc!=2) {
cout << "Usage: PR <filename>\n";
return 1;
}
ifstream in(argv[1], ios::in | ios::binary);
if(!in) {
cout << "Cannot open file.";
return 1;
}
while(in) { // in will be false when eof is reached
in.get(ch);
if(in) cout << ch;
}
return 0;
}Use read() to input blocks of binary data.
#include <iostream>
#include <fstream>
using namespace std;
struct inventory {
char item[20];
int quantity;
double cost;
};
int main()
{
ifstream fin("InvDat.dat", ios::in | ios::binary);
if(!fin) {
cout << "Cannot open file.\n";
return 1;
}
inventory inv[3];
for(int i=0; i<3; i++)
fin.read((char *) &inv[i], sizeof(inventory));
fin.close();
if(!fin.good()) {
cout << "A file error occurred.\n";
return 1;
}
for(int i=0; i < 3; i++) {
cout << inv[i].item << "\n";
cout << " Quantity on hand: " << inv[i].quantity;
cout << "\n Cost: " << inv[i].cost << "\n\n";
}
return 0;
}Use write() to output a block of binary data.
#include <iostream>
#include <fstream>
#include <cstring>
using namespace std;
struct inventory {
char item[20];
int quantity;
double cost;
};
int main()
{
ofstream fout("InvDat.dat", ios::out | ios::binary);
if(!fout) {
cout << "Cannot open file.\n";
return 1;
}
inventory inv[3];
strcpy(inv[0].item,"A");
inv[0].quantity = 3;
inv[0].cost = 9.99;
strcpy(inv[1].item, "B");
inv[1].quantity = 12;
inv[1].cost = 7.85;
strcpy(inv[2].item, "C");
inv[2].quantity = 19;
inv[2].cost = 2.75;
for(int i=0; i<3; i++)
fout.write((const char *) &inv[i], sizeof(inventory));
fout.close();
if(!fout.good()) {
cout << "A file error occurred.";
return 1;
}
return 0;
}Write Unformatted Binary Data to a File
#include <iostream>
#include <fstream>
#include <cstdlib>
using namespace std;
struct inventory {
char item[20];
int quantity;
double cost;
};
int main(int argc, char *argv[])
{
inventory entry;
long record_num = 2;
ifstream fInvDB("InvDat.dat", ios::in | ios::binary);
if(!fInvDB) {
cout << "Cannot open file.\n";
return 1;
}
fInvDB.seekg(sizeof(inventory) * record_num, ios::beg);
fInvDB.read((char *) &entry, sizeof(inventory));
fInvDB.close();
if(!fInvDB.good()) {
cout << "A file error occurred.\n";
return 1;
}
}
