C++ Tutorial/File Stream/class save load
Содержание
Read class data from file
<source lang="cpp">#include <iostream> using std::cerr; using std::cout; using std::endl; using std::fixed; using std::ios; using std::left; using std::right; using std::showpoint;
- include <string>
using std::string;
- include <iomanip>
using std::setprecision; using std::setw;
- include <fstream>
using std::ifstream; using std::ostream;
- include <cstdlib>
using std::exit; // exit function prototype class Account { public:
Account( )
{
}
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;
};
void outputLine( ostream&, const Account & ); // prototype int main() {
ifstream inCredit( "credit.dat", ios::in );
if ( !inCredit )
{
cerr << "File could not be opened." << endl;
exit( 1 );
} // end if
Account client; // create record
inCredit.read( reinterpret_cast< char * >( &client ), sizeof( Account ) );
while ( inCredit && !inCredit.eof() )
{
if ( client.getAccountNumber() != 0 )
outputLine( cout, client );
inCredit.read( reinterpret_cast< char * >( &client ),sizeof( Account ) );
}
return 0;
} void outputLine( ostream &output, const Account &record ) {
output << left << setw( 10 ) << record.getAccountNumber()
<< setw( 16 ) << record.getLastName()
<< setw( 11 ) << record.getFirstName()
<< setw( 10 ) << setprecision( 2 ) << right << fixed
<< showpoint << record.getBalance() << endl;
}</source>
1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20 1 AAAAA BBBBB 1.20
Read person object from disk
<source lang="cpp">#include <fstream>
- include <iostream>
using namespace std; class person{
protected:
char name[80];
short age;
public:
void showData(){
cout << "Name: " << name << endl;
cout << "Age: " << age << endl;
}
}; int main(){
person pers;
ifstream infile("PERSON.DAT", ios::binary);
infile.read( reinterpret_cast<char*>(&pers), sizeof(pers) );
pers.showData();
return 0;
}</source>
reads and writes several objects to disk
<source lang="cpp">#include <fstream>
- include <iostream>
using namespace std; class person{
protected:
char name[80];
int age;
public:
void getData(){
cout << "\n Enter name: "; cin >> name;
cout << " Enter age: "; cin >> age;
}
void showData(){
cout << "\n Name: " << name;
cout << "\n Age: " << age;
}
}; int main(){
char ch;
person pers;
fstream file;
file.open("GROUP.DAT", ios::app | ios::out | ios::in | ios::binary );
do {
cout << "\nEnter person"s data:";
pers.getData();
file.write( reinterpret_cast<char*>(&pers), sizeof(pers) );
cout << "Enter another person (y/n)? ";
cin >> ch;
}while(ch=="y");
file.seekg(0);
file.read( reinterpret_cast<char*>(&pers), sizeof(pers) );
while( !file.eof() ){
cout << "\nPerson:";
pers.showData();
file.read( reinterpret_cast<char*>(&pers), sizeof(pers) );
}
cout << endl;
return 0;
}</source>
Save class to a file
<source lang="cpp">#include <iostream> using std::cerr; using std::cin; using std::cout; using std::endl; using std::ios;
- include <iomanip>
using std::setw;
- include <fstream>
using std::fstream;
- include <cstdlib>
using std::exit; // exit function prototype
- 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() {
fstream outCredit( "credit.dat", ios::in | ios::out | ios::binary );
// exit program if fstream cannot open file
if ( !outCredit )
{
cerr << "File could not be opened." << endl;
exit( 1 );
} // end if
Account client(1,"AAAAA","BBBBB",1.2);
// seek position in file of user-specified record
outCredit.seekp( ( client.getAccountNumber() - 1 ) * sizeof( Account ) );
// write user-specified information in file
outCredit.write( reinterpret_cast< const char * >( &client ),sizeof( Account ) );
return 0;
}</source>
saves person object to disk
<source lang="cpp">#include <fstream>
- include <iostream>
using namespace std; class person
{
protected:
char name[80];
short age;
public:
void getData(){
cout << "Enter name: "; cin >> name;
cout << "Enter age: "; cin >> age;
}
}; int main(){
person pers;
pers.getData();
ofstream outfile("PERSON.DAT", ios::binary);
outfile.write(reinterpret_cast<char*>(&pers), sizeof(pers));
return 0;
}</source>
Writing a Class to a File
<source lang="cpp">#include <fstream>
- include <iostream>
using namespace std; class Animal { public:
Animal(int weight, long days):itsWeight(weight),itsNumberDaysAlive(days){}
~Animal(){}
int GetWeight()const { return itsWeight; }
void SetWeight(int weight) { itsWeight = weight; }
long GetDaysAlive()const { return itsNumberDaysAlive; }
void SetDaysAlive(long days) { itsNumberDaysAlive = days; }
private:
int itsWeight; long itsNumberDaysAlive;
}; int main(){
ofstream fout("text.txt",ios::binary);
if (!fout)
{
cout << "Unable to open for writing.\n";
return(1);
}
Animal Bear(50,100);
fout.write((char*) &Bear,sizeof Bear);
fout.close();
ifstream fin("text.txt",ios::binary);
if (!fin)
{
cout << "Unable to open for reading.\n";
return(1);
}
Animal BearTwo(1,1);
cout << "BearTwo weight: " << BearTwo.GetWeight() << endl;
cout << "BearTwo days: " << BearTwo.GetDaysAlive() << endl;
fin.read((char*) &BearTwo, sizeof BearTwo);
cout << "BearTwo weight: " << BearTwo.GetWeight() << endl;
cout << "BearTwo days: " << BearTwo.GetDaysAlive() << endl;
fin.close();
return 0;
}</source>
