问一种将对象保存为二进制文件的有效方法

EN

#include <fstream>
#include <algorithm>

using std::ofstream;
using std::fill;

class binary_stream_interface
{
    virtual void    load_from_buffer(const unsigned char *& buf_ptr) = 0;
    virtual size_t  size_on_stream(void) const = 0;
    virtual void    store_to_buffer(unsigned char *& buf_ptr) const = 0;
};

struct Pet
    : public binary_stream_interface,
    max_name_length(32)
{
    std::string     name;
    unsigned int    age;
    const unsigned int  max_name_length;

    void    load_from_buffer(const unsigned char *& buf_ptr)
        {
            age = *((unsigned int *) buf_ptr);
            buf_ptr += sizeof(unsigned int);
            name = std::string((char *) buf_ptr);
            buf_ptr += max_name_length;
            return;
        }
    size_t  size_on_stream(void) const
    {
        return sizeof(unsigned int) + max_name_length;
    }
    void    store_to_buffer(unsigned char *& buf_ptr) const
    {
        *((unsigned int *) buf_ptr) = age;
        buf_ptr += sizeof(unsigned int);
        std::fill(buf_ptr, 0, max_name_length);
        strncpy((char *) buf_ptr, name.c_str(), max_name_length);
        buf_ptr += max_name_length;
        return;
    }
};


int main(void)
{
    Pet dog;
    dog.name = "Fido";
    dog.age = 5;
    ofstream    data_file("pet_data.bin", std::ios::binary);

    // Determine size of buffer
    size_t  buffer_size = dog.size_on_stream();

    // Allocate the buffer
    unsigned char * buffer = new unsigned char [buffer_size];
    unsigned char * buf_ptr = buffer;

    // Write / store the object into the buffer.
    dog.store_to_buffer(buf_ptr);

    // Write the buffer to the file / stream.
    data_file.write((char *) buffer, buffer_size);

    data_file.close();
    delete [] buffer;
    return 0;
}

class Many_Strings
    : public binary_stream_interface
{
    enum {MAX_STRING_SIZE = 32};

    size_t    size_on_stream(void) const
    {
        return m_string_container.size() * MAX_STRING_SIZE  // Total size of strings.
               + sizeof(size_t); // with room for the quantity variable.
    }

    void      store_to_buffer(unsigned char *& buf_ptr) const
    {
        // Treat the vector<string> as a variable length field.
        // Store the quantity of strings into the buffer,
        //     followed by the content.
        size_t string_quantity = m_string_container.size();
        *((size_t *) buf_ptr) = string_quantity;
        buf_ptr += sizeof(size_t);

        for (size_t i = 0; i < string_quantity; ++i)
        {
            // Each string is a fixed length field.
            // Pad with '\0' first, then copy the data.
            std::fill((char *)buf_ptr, 0, MAX_STRING_SIZE);
            strncpy(buf_ptr, m_string_container[i].c_str(), MAX_STRING_SIZE);
            buf_ptr += MAX_STRING_SIZE;
        }
    }
    void load_from_buffer(const unsigned char *& buf_ptr)
    {
        // The actual coding is left as an exercise for the reader.
        // Psuedo code:
        //     Clear / empty the string container.
        //     load the quantity variable.
        //     increment the buffer variable by the size of the quantity variable.
        //     for each new string (up to the quantity just read)
        //        load a temporary string from the buffer via buffer pointer.
        //        push the temporary string into the vector
        //        increment the buffer pointer by the MAX_STRING_SIZE.
        //      end-for
     }
     std::vector<std::string> m_string_container;
};

fstream fr("test.txt", ios_base::out | ios_base::binary );
for( int i =0;i <_countof(arr);i++)
    fr << arr[i] << ' ';

fr.close();

fstream fw("test.txt", ios_base::in| ios_base::binary);

int j = 0;
while( fw.eof() || j < _countof(arrout))
{
    fw >> arrout[j++];
}