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，我只会把整个对象正常地写入二进制文件，但如果我现在这样做，字符串也可以很容易地读取。
因此，我决定分别编写结构的每个属性。我使用字符串的方式与Stackoverflow答案中提到的相同。
这是将结构保存到name.bin文件中的主要函数。
void saveFileBin(std::string nameOfFile) {
Person people[SIZE_OF_ARRAY] =
{Person("Name1", "lastName2", Address("Street1", "City1", "111"), Date(1, 1, 1111)),
Person("Name2", "lastName2", 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");
}
};
并且这是用于将每个属性写入文件的函数。
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());
}
生成的文件中的所有内容都是可读的纯文本。尽管如果我在主方法中调用myFile.write((char*)people, sizeof(people));，那么它会正确显示不可读的字符，但字符串变量仍然是正常读取的。这就是为什么我将所有变量转换为字符串，然后将其全部写入bin文件。
为什么我的方法仍然显示所有字符串，就像它甚至不是二进制文件一样？即使我有std:：ios：：binary作为参数？
输出文件包含以下内容：
Name1lastName1Street11111City11111111Name2lastName2Street22222City22222222Name3lastName3Street33333City3333333
然而，如果我将整个结构写入二进制文件，它看起来像这样：
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 的标题
#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
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:的六进制转储
00000000 08 00 41 6e 74 72 6f 70 68 79 |..Antrophy|
0000000a
coliru上的实时演示
注意：
考虑如何写入长度(限制为16位(。这可以类似于序列化整数值来完成。
C++FAQ:提供了一个(IMHO(好的介绍
序列化和非序列化
组合型Person:二进制I/O的扩展样本
#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] = ' ';
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, const std::string &str)
{
// write length of string (two bytes, 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(), size);
}
void readString(std::istream &in, 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
coliru上的实时演示
注意：
与其他地方发现的简单out.write((char*)value, sizeof value);相比，积分值(readInt()和writeInt()(的二进制I/O类型可能看起来过于复杂。我以一种更便携的方式完成了这项工作，当在具有不同endianes和/或不同大小积分的不同平台上使用时，这种方式甚至可以工作。