写入二进制文件 [英] writing into binary files

问题描述

#include <iostream>
#include <fstream>

using namespace std;

class info {

private:
    char name[15];
    char surname[15];
    int age;
public:
    void input(){
        cout<<"Your name:"<<endl;
            cin.getline(name,15);
        cout<<"Your surname:"<<endl;
        cin.getline(surname,15);
        cout<<"Your age:"<<endl;
        cin>>age;
        to_file(name,surname,age);
    }

    void to_file(char name[15], char surname[15], int age){
        fstream File ("example.bin", ios::out  | ios::binary | ios::app);
    // I doesn't know how to fill all variables(name,surname,age) in 1 variable (memblock) 
        //example File.write ( memory_block, size ); 

File.close();
    }

};

int main(){

info ob;
ob.input();

 return 0;
}

我不知道该怎么写1个多变量到一个文件中，请大家帮忙，我包括一个例子），也许有更好的方法来写一个文件，请帮助我，这给我很难解决的。

I don't know how to write more than 1 variable into a file, please help, I included an example ;) Maybe there are better ways to write to a file, please help me with this, it's to hard for me to solve.

推荐答案

对于文本的文件，你可以使用类似＆LT每行轻松输出一个变量;＆LT; 给您的std :: COUT 使用的一个。

For a text file, you could easily output one variable per line using a similar << to the one you use with std::cout.

对于二进制的文件，你需要使用<一个href=\"http://en.cp$p$pference.com/w/cpp/io/basic_ostream/write\"><$c$c>std::ostream::write(),其中写一个字节序列。为了您的年龄属性，你需要 reinter pret_cast 这常量字符* 并要持有 INT 为您的机器架构写入的字节数。请注意，如果你打算读不同的机器上这个二进制日期，就必须采取字大小和字节顺序的考虑。我还建议您零的名称和姓缓冲区之前你使用它们，免得你最终未初始化内存的文物在您的二进制文件。

For a binary file, you need to use std::ostream::write(), which writes a sequence of bytes. For your age attribute, you'll need to reinterpret_cast this to const char* and write as many bytes as is necessary to hold an int for your machine architecture. Note that if you intend to read this binary date on a different machine, you'll have to take word size and endianness into consideration. I also recommend that you zero the name and surname buffers before you use them lest you end up with artefacts of uninitialised memory in your binary file.

此外，没有必要给类的属性传递到 to_file（）方法。

Also, there's no need to pass attributes of the class into the to_file() method.

#include <cstring>
#include <fstream>
#include <iostream>

class info
{
private:
    char name[15];
    char surname[15];
    int age;

public:
    info()
        :name()
        ,surname()
        ,age(0)
    {
        memset(name, 0, sizeof name);
        memset(surname, 0, sizeof surname);
    }

    void input()
    {
        std::cout << "Your name:" << std::endl;
        std::cin.getline(name, 15);

        std::cout << "Your surname:" << std::endl;
        std::cin.getline(surname, 15);

        std::cout << "Your age:" << std::endl;
        std::cin >> age;

        to_file();
    }

    void to_file()
    {
        std::ofstream fs("example.bin", std::ios::out | std::ios::binary | std::ios::app);
        fs.write(name, sizeof name);
        fs.write(surname, sizeof surname);
        fs.write(reinterpret_cast<const char*>(&age), sizeof age);
        fs.close();
    }
};

int main()
{
    info ob;
    ob.input();
}

一个采样数据文件可能是这样的：

A sample data file may look like this:

% xxd example.bin
0000000: 7573 6572 0000 0000 0000 0000 0000 0031  user...........1
0000010: 3036 3938 3734 0000 0000 0000 0000 2f00  069874......../.
0000020: 0000                                     ..

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