二进制流文件的读，写（二）

基于模板类，模板函数的二进制文件读写，可深化适应于任何类的读写操作

/* bstream.h */
#include <iostream>
#include <fstream>

using namespace std;

// Binary output file stream

class bofstream:public ofstream {
public:
    bofstream(const char *fn)
        :ofstream(fn, ios::out|ios::binary) { }
    void writeBytes(const void *, int);
    template < class T>
    bofstream & operator<< (const T & data);
};

template <class T>
bofstream & bofstream::operator<< (const T & data)  //调用时会带this指针，因为返回了bofstream对象，与下面的重载区别
{
    writeBytes(&data, sizeof(data));
    return * this;
}

//Binary input file stream
class bifstream:public ifstream {
public:
    bifstream(const char *fn)
        :ifstream(fn, ios::in|ios::binary) { }
    void readBytes(void *, int);
    template <class T>
    bifstream & operator>> (T & data);
};

template <class T>
bifstream & bifstream::operator>> (T & data)
{
    readBytes(&data, sizeof(data));
    return * this;
}

/* bstream.cpp */
#include "bstream.h"
void bofstream::writeBytes(const void * p, int len)
{
    if (!p) return;
    if (len <= 0) return;
    write((char *)p, len);
}

void bifstream::readBytes(void *p,int len)
{
    if(!p) return;
    if (len <= 0) return;
    read((char *)p, len);
}

使用了模板函数，其它均和前例保持一样。。

/* tbdouble.cpp */
/* 基于模板类的测试实例*/
#include
#include
#include "bstream.h"

using namespace std;

#define FILENAME "tbdouble.dat"

int main()
{
    //construct binary output file
    bofstream bofs(FILENAME);
    if (!bofs) {
        cerr << "Error:unable to write to " << FILENAME <        exit(1);
        }

    //write values and close file
    double d = 3.14159;
    bofs << d << d * d << d * d * d;
    bofs.close();

    //construct binary input file
    bifstream bifs(FILENAME);
    if (!bifs) {
        cerr << "Error: uanble to open " << FILENAME << endl;
        exit(2);
        }

    //Read and display values from file
    int count = 0;
    cout.precision(8);
    bifs >> d;    // reading data by sizeof(d) byte
    while (!bifs.eof()) {
        cout << ++count << ": " << d << endl;
        bifs >> d;
        }

    return 0;
}

对类对象的读取，写入。。。。

/* tanyclass.h
* 使用类读取和写入二进制形式的类
* 对象
*/
#include <iostream>

using namespace std;

class TAnyClass {
private:
    int x;
    int y;
public:
    friend ostream & operator<< (ostream &, const TAnyClass &); //调用时不带this指针，与上面的区别。声明为友元函数，可以使ostream类函数访问类的私有变量.调用的是标准的cin,cout istream/ostream
    friend istream & operator>> (istream &, TAnyClass &);
public:
    TAnyClass():x(0), y(0) { }
    TAnyClass(int x, int y):x(x), y(y) { }
};

/* tanyclass.cpp */
#include
#include "tanyclass.h"

using namespace std;

//Implements over loaded ostream output operator
ostream & operator<< (ostream &os, const TAnyClass &c)
{
    os << " - - TAnyClass object - -" << endl;
    os << "x == " << c.x << "; ";
    os << "y == " << c.y << endl;
    return os;
}

//Implements overloaded istream input operator
istream & operator>> (istream &is, TAnyClass &c)
{
    cout << "Enter value for X: ";
    is >> c.x;
    cout << "Enter value for Y: ";
    is >> c.y;
    return is;
}

#include
#include     //Need exit()
#include "tanyclass.h"
#include "bstream.h"

using namespace std;

#define FILENAME "tbobj.dat"

int main()
{
    bofstream bofs(FILENAME);
    if (!bofs) {
        cerr << "Error: unable to write to " << FILENAME << endl;
        exit(1);
        }

    TAnyClass obj; //Default object
    //Prompt user to enter object values
    cin >> obj;
    //Write object to disk and close file
    cout << "Writing object to disk" << endl;
    bofs << obj;   //如何确定调用哪个重载函数 "<<" ?
    bofs.close();

    //construct binary input file
    cout << "Operating file" << endl;
    bifstream bifs(FILENAME);
    if (!bifs) {
        cerr << "Error:unable to open " << FILENAME << endl;
        exit(2);
        }

    //Read object from file. Use a new TAnyClass
    //object to be sure values are new.
    cout << "Reading object from disk" << endl;
    TAnyClass newObject;
    bifs >> newObject;

    cout << "Object from disk" << endl;
    cout << newObject;

    bifs.close();

    return 0;
}

g++ -g tbobj.cpp bstream.o tanyclass.o -o tbobj