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将结构写入二进制文件后，该文件仍然具有普通字符，而不是不可读的字符

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我正在尝试将结构写入二进制文件。该结构由字符串和整数组成。如果没有字符串，我只是将整个对象带入正常情况下将其写入二进制文件，但是如果现在执行该操作，则也可以轻松读取字符串。

因此，我决定分别编写该结构的每个属性。我正在使用字符串the same way like it's mentioned in this Stackoverflow answer。

这是应该将结构保存到 name.bin 文件中的主要功能。

void saveFileBin(std::string nameOfFile) {
    Person people[SIZE_OF_ARRAY] =
    {Person("Name1","lastName2",Address("Street1","City1","111"),Date(1,1,1111)),Person("Name2",Address("Street2","City2","222"),Date(2,2,2222)),Person("Name3","lastName3",Address("Street3","City3","333"),Date(3,3,3333))};

    std::ofstream myFile(nameOfFile + ".bin",std::ios::binary);
    if (myFile.is_open())
    {
        for (int i = 0; i < SIZE_OF_ARRAY; i++)
        {
            people[i].write(&myFile);
        }
        myFile.close();

        std::cout << "The entire thing is in memory";
    }
    else 
    {
        throw std::exception("Unable to open file");
    }
};

这是用于将每个属性写入文件的功能。

void Person::write(std::ofstream* out)
{
    out->write(_name.c_str(),_name.size());
    out->write(_lastName.c_str(),_lastName.size());
    out->write(_residence.getStreet().c_str(),_residence.getStreet().size());
    out->write(_residence.getZip().c_str(),_residence.getZip().size());
    out->write(_residence.getcity().c_str(),_residence.getcity().size());
    std::string day = std::to_string(_birthDate.getDay());
    std::string month = std::to_string(_birthDate.getMonth());
    std::string year = std::to_string(_birthDate.getYear());
    out->write(day.c_str(),day.size());
    out->write(month.c_str(),month.size());
    out->write(year.c_str(),year.size());
}

生成的文件具有纯文本可读的所有内容。 尽管如果我改为在主方法调用myFile.write((char*)people,sizeof(people));中使用它，则它可以正确显示不可读的字符，但仍可以正常读取字符串变量。这就是为什么我将所有变量都转换为字符串，然后将其完全写入bin文件的原因。

为什么我的方法仍然显示所有字符串，甚至不是二进制文件？即使我将std :: ios :: binary作为参数？

输出文件包含以下内容：

Name1lastName1Street11111City11111111Name2lastName2Street22222City22222222Name3lastName3Street33333City3333333

如果我将整个结构写入二进制文件，则如下所示：

     lÊ87  Name1 ÌÌÌÌÌÌÌÌÌÌ              à^Ê87  lastName1 ÌÌÌÌÌÌ                  Ð_Ê87  Street1 ÌÌÌÌÌÌÌÌ              ÐdÊ87  City1 ÌÌÌÌÌÌÌÌÌÌ               bÊ87  111 ÌÌÌÌÌÌÌÌÌÌÌÌ                    W  ÌÌÌÌ`kÊ87  Name2 ÌÌÌÌÌÌÌÌÌÌ              fÊ87  lastName2 ÌÌÌÌÌÌ                 €iÊ87  Street2 ÌÌÌÌÌÌÌÌ              PbÊ87  City2 ÌÌÌÌÌÌÌÌÌÌ              ÐiÊ87  222 ÌÌÌÌÌÌÌÌÌÌÌÌ                    ®  ÌÌÌÌ€dÊ87  Name3 ÌÌÌÌÌÌÌÌÌÌ               `Ê87  lastName3 ÌÌÌÌÌÌ                p`Ê87  Street3 ÌÌÌÌÌÌÌÌ               gÊ87  City3 ÌÌÌÌÌÌÌÌÌÌ              ðbÊ87  333 ÌÌÌÌÌÌÌÌÌÌÌÌ                    
  ÌÌÌÌ lÊ87  Name1 ÌÌÌÌÌÌÌÌÌÌ              à^Ê87  lastName1 ÌÌÌÌÌÌ                Ð_Ê87  Street1 ÌÌÌÌÌÌÌÌ              ÐdÊ87  City1 ÌÌÌÌÌÌÌÌÌÌ               bÊ87  111 ÌÌÌÌÌÌÌÌÌÌÌÌ                    W  ÌÌÌÌ`kÊ87  Name2 ÌÌÌÌÌÌÌÌÌÌ              fÊ87  lastName2 ÌÌÌÌÌÌ                 €iÊ87  Street2 ÌÌÌÌÌÌÌÌ              PbÊ87  City2 ÌÌÌÌÌÌÌÌÌÌ              ÐiÊ87  222 ÌÌÌÌÌÌÌÌÌÌÌÌ                    ®  ÌÌÌÌ€dÊ87  Name3 ÌÌÌÌÌÌÌÌÌÌ               `Ê87  lastName3 ÌÌÌÌÌÌ                p`Ê87  Street3 ÌÌÌÌÌÌÌÌ               gÊ87  City3 ÌÌÌÌÌÌÌÌÌÌ              ðbÊ87  333 ÌÌÌÌÌÌÌÌÌÌÌÌ                    
  ÌÌÌÌ lÊ87  Name1 ÌÌÌÌÌÌÌÌÌÌ              à^Ê87  lastName1 ÌÌÌÌÌÌ                Ð_Ê87  Street1 ÌÌÌÌÌÌÌÌ              ÐdÊ87  City1 ÌÌÌÌÌÌÌÌÌÌ               bÊ87  111 ÌÌÌÌÌÌÌÌÌÌÌÌ                    W  ÌÌÌÌ`kÊ87  Name2 ÌÌÌÌÌÌÌÌÌÌ              fÊ87  lastName2 ÌÌÌÌÌÌ                 €iÊ87  Street2 ÌÌÌÌÌÌÌÌ              PbÊ87  City2 ÌÌÌÌÌÌÌÌÌÌ              ÐiÊ87  222 ÌÌÌÌÌÌÌÌÌÌÌÌ                    ®  ÌÌÌÌ€dÊ87  Name3 ÌÌÌÌÌÌÌÌÌÌ               `Ê87  lastName3 ÌÌÌÌÌÌ                p`Ê87  Street3 ÌÌÌÌÌÌÌÌ               gÊ87  City3 ÌÌÌÌÌÌÌÌÌÌ              ðbÊ87  333 ÌÌÌÌÌÌÌÌÌÌÌÌ                    
  ÌÌÌÌ

编辑： 根据要求，这里是Person.h的标头

#pragma once
#ifndef PERSON_H
#define PERSON_H
#include <string.h>
#include "Address.h"
#include "Date.h"
#include <fstream>

struct Person {
public:
    Person(std::string name,std::string last_name,Address _residence,Date birthDate);
    Person();
    friend std::ostream& operator<<(std::ostream& os,const Person& p);
    friend std::istream& operator>>(std::istream& is,Person& p);
    std::string getName() const { return _name; }
    std::string getLastName() const { return _lastName; };
    Address getResidence() const { return _residence; };
    Date getDate() const { return _birthDate; };
    void read(std::ifstream *in);
    void write(std::ofstream *out);
private:
    std::string _name;
    std::string _lastName;
    Address _residence;
    Date _birthDate;
};
#endif // !PERSON_H
luxiaofeng_374 回答：将结构写入二进制文件后，该文件仍然具有普通字符，而不是不可读的字符

用于序列化std::string（长度限制为≤65536个字符）的示例：

#include <cassert>
#include <iostream>
#include <fstream>

void writeString(std::ostream &out,const std::string &str)
{
  // write length of string (two bytes,little endian)
  assert(str.size() <= 1 << 16);
  const size_t size = str.size();
  char buffer[2] = { (char)(size & 0xff),(char)(size >> 8 & 0xff) };
  out.write(buffer,sizeof buffer)
  // write string contents
  && out.write(str.c_str(),size);
}

void readString(std::istream &in,std::string &str)
{
  // read length
  char buffer[2];
  if (!in.read(buffer,2)) return; // failed
  const size_t size = (unsigned char)buffer[0] | (unsigned char)buffer[1] << 8;
  // allocate size
  str.resize(size);
  // read contents
  in.read(&str[0],size);
}

int main()
{
  // sample
  std::string name = "Antrophy";
  // write binary file
  { std::ofstream out("test.dat",std::ios::binary);
    writeString(out,name);
  } // closes file
  // reset sample
  name = "";
  // read binary file
  { std::ifstream in("test.dat",std::ios::binary);
    readString(in,name);
  } // closes file
  // report result
  std::cout << "name: '" << name << "'\n";
}

输出：

name: 'Antrophy'

test.dat的十六进制转储：

00000000  08 00 41 6e 74 72 6f 70  68 79                    |..Antrophy|
0000000a

Live Demo on coliru

注意：

考虑如何写长度（限制为16位）。可以像序列化整数值一样完成此操作。

C ++ FAQ提供了一个（IMHO）很好的介绍：

Serialization and Unserialization

组合类型为Person的二进制I / O的扩展示例：

#include <cassert>
#include <iostream>
#include <fstream>

template <size_t nBytes,typename VALUE>
std::ostream& writeInt(std::ostream &out,VALUE value)
{
  const size_t size = sizeof value;
  char buffer[nBytes];
  const size_t n = std::min(nBytes,size);
  for (size_t i = 0; i < n; ++i) {
    buffer[i] = (char)(value >> 8 * i & 0xff);
  }
  for (size_t i = size; i < nBytes; ++i) buffer[i] = '\0';
  return out.write(buffer,nBytes);
}

template <size_t nBytes,typename VALUE>
std::istream& readInt(std::istream &in,VALUE &value)
{
  const size_t size = sizeof value;
  char buffer[nBytes];
  if (in.read(buffer,nBytes)) {
    value = (VALUE)0;
    const size_t n = std::min(nBytes,size);
    for (size_t i = 0; i < n; ++i) {
      value |= (VALUE)(unsigned char)buffer[i] << 8 * i;
    }
  }
  return in;
}

void writeString(std::ostream &out,little endian)
  assert(str.size() <= 1 << 16);
  const size_t size = str.size();
  writeInt<2>(out,size)
  // write string contents
  && out.write(str.c_str(),std::string &str)
{
  // read length
  std::uint16_t size = 0;
  if (!readInt<2>(in,size)) return; // failed
  // allocate size
  str.resize(size);
  // read contents
  in.read(&str[0],size);
}

struct Person {
  std::string lastName,firstName;
  int age;

  void write(std::ostream&) const;
  void read(std::istream&);
};

void Person::write(std::ostream &out) const
{
  writeString(out,lastName);
  writeString(out,firstName);
  writeInt<2>(out,age);
}

void Person::read(std::istream &in)
{
  readString(in,lastName);
  readString(in,firstName);
  std::int16_t age; assert(sizeof age == 2); // ensure proper sign extension
  if (readInt<2>(in,age)) this->age = age;
}

int main()
{
  // sample
  Person people[2] = {
    { "Mustermann","Klaus",23 },{ "Doe","John",-111 }
  };
  // write binary file
  { std::ofstream out("test.dat",std::ios::binary);
    for (const Person &person : people) person.write(out);
  } // closes file
  // read sample
  Person peopleIn[2] = {
    { "","",-1 },{ "",-1 }
  };
  // read binary file
  { std::ifstream in("test.dat",std::ios::binary);
    for (Person &person : peopleIn) person.read(in);
  } // closes file
  // report result
  int i = 1;
  for (const Person &person : peopleIn) {
    std::cout << "person " << i++ << ": '"
      << person.firstName << ' ' << person.lastName
      << ",age: " << person.age << '\n';
  }
}

输出：

person 1: 'Klaus Mustermann,age: 23
person 2: 'John Doe,age: -111

test.dat的十六进制转储：

00000000  0a 00 4d 75 73 74 65 72  6d 61 6e 6e 05 00 4b 6c  |..Mustermann..Kl|
00000010  61 75 73 17 00 03 00 44  6f 65 04 00 4a 6f 68 6e  |aus....Doe..John|
00000020  91 ff                                             |..|
00000022

Live Demo on coliru

注意：

与其他位置的简单readInt()相比，整数值（writeInt()和out.write((char*)value,sizeof value);）的二进制I / O看起来过于复杂。我以一种更便携的方式做到了这一点，甚至可以在具有不同字节序和/或不同积分大小的不同平台上使用。

binary-databinaryfilesc++file-writing
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