c++ - 读写二进制文件

Question

我对二进制文件有疑问。我想创建一个二进制文件，其中包含程序的版本号和颠覆号。然后，我想从该文件中先读取 sizeof(uint16_t) 字节，然后再读取 sizeof(uint16_t) 字节，从而读取里面的内容。但我不知道该怎么做。 (我什至不接近)

#include <iostream>
#include <fstream>
#include <stdint.h>

using namespace std;

void   saving_uint16_t(uint16_t number);
uint16_t reading_uint16_t();

int where = 0;

int main() {

    const uint16_t number_version = 2;
    cout << "Version: " << number_version << endl;
    cout << "Saving number..." << endl;
    saving_uint16_t(number_version);

    const uint16_t number_subversion = 1;
    cout << "Subversion: " << number_subversion << endl;
    cout << "Saving number..." << endl;
    saving_uint16_t(number_subversion);

    cout << "Read numbers:\nVersion: " << reading_uint16_t() << "\nSubversion: " << reading_uint16_t() << endl << endl;

    return 0;
}

void saving_uint16_t(uint16_t number) {

    ofstream data("numbers.bin",  ios::app | ios::binary);
    data.write(reinterpret_cast<char*>(&number), sizeof(uint16_t));
}

uint16_t reading_uint16_t(){

    ifstream data("numbers.bin", ios::binary);
    data.seekg(where);
    where = where + 16;
    uint16_t result;
    data.read(reinterpret_cast<char*>(&result), sizeof(uint16_t));
    return result;
}

我真的很陌生，我不知道该用什么。

输出:

Version: 3
Saving number...
Subversion: 7
Saving number...
Read numbers:
Version: 3
Subversion: 3

然后我更改了数字，但我仍然得到:

Version: 2
Saving number...
Subversion: 1
Saving number...
Read numbers:
Version: 3
Subversion: 3

应该是:

Version: 2
Saving number...
Subversion: 1
Saving number...
Read numbers:
Version: 2
Subversion: 1

我想补充一点，我的目标是创建一个二进制文件，其中有两个 uint16_t 变量，然后分别从文件中读取它们。所以我可以写 Version: (first uint16_t), Subversion: (second uint16_t)

Answer 1

因此，通过查看提取 numbers.bin 中所有 uint16_t 的函数，您的理解可能会得到改善。假设 numbers.bin 包含的所有内容都是 uint16_ts，那么您可以这样做:

ifstream data("numbers.bin", ios_base::binary | ios_base::ate); // Starting at the end of the stream for sizing
const auto count = data.tellg() / sizeof(uint16_t); // tellg will report the number of characters in the file, sizeof(uint16_t) the numberof characters required to store a uint16_t, thus the division will give us the number of uint16_ts in numbers.bin
vector<uint16_t> numbers(count); // Allocate storage for all the uint16_ts in numbers.bin

data.seekg(0U, ios_base::beg); // Move the input position indicator to the beginning of the file for reading
data.read(reinterpret_cast<char*>(numbers.data()), count * sizeof(uint16_t)); // Slurp the file into numbers

---

与访问 numbers.bin 的特定元素类似，我们需要相应地设置位置:

ifstream data("numbers.bin", ios_base::binary); // Starting at the beginning of the file
const auto where = 2U; // This offset will be 0 based
uint16_t number; // Allocate storage for the element at where

data.seekg(where * sizeof(uint16_t)); // Move the input position indicator to the specified uint16_t
data.read(reinterpret_cast<char*>(&number), sizeof(number)); // Read the element into number

Live Example