C++ 写入二进制文件
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writing into binary files
提问by Wizard
#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;
}
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.
我不知道如何将 1 个以上的变量写入文件，请帮忙，我包含了一个示例；) 也许有更好的写入文件的方法，请帮我解决这个问题，这对我来说很难解决。
回答by Johnsyweb
For a textfile, you could easily output one variable per line using a similar <<to the one you use with std::cout.
对于文本文件，您可以<<使用与std::cout.
For a binaryfile, you need to use std::ostream::write(), which writes a sequence of bytes. For your ageattribute, you'll need to reinterpret_castthis to const char*and write as many bytes as is necessary to hold an intfor your machine architecture. Note that if you intend to read this binary date on a different machine, you'll have to take word sizeand endiannessinto consideration. I also recommend that you zero the nameand surnamebuffers before you use them lest you end up with artefacts of uninitialised memory in your binary file.
对于二进制文件，您需要使用std::ostream::write()，它会写入一个字节序列。对于您的age属性，您需要将reinterpret_cast其const char*写入并写入尽可能多的字节以容纳int您的机器架构。请注意，如果您打算在另一台机器上读取此二进制日期，则必须考虑字长和字节序。我还建议您在使用name和surname缓冲区之前将它们归零，以免最终在二进制文件中出现未初始化内存的人工制品。
Also, there's no need to pass attributes of the class into the to_file()method.
此外，无需将类的属性传递到to_file()方法中。
#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();
}
A sample data file may look like this:
示例数据文件可能如下所示：
% 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 ..
回答by Dani
File.write(name, 15);
File.write(surname, 15);
File.write((char *) &age, sizeof(age));
