在 cpp 中读取二进制文件有问题吗？

Question

I have a binary file called "input.bin" where every character is of 4 bits. The file contains this kind of data:

0f00 0004 0018 0000 a040 420f 0016 030b
0000 8000 0000 0000 0000 0004 0018 0000

where 0f is the first byte.

I want to read this data and to do that, I am using the following code:

#include <string>
#include <iostream>
#include <fstream>

int main()
{
      char buffer[100];
      std::ifstream myFile ("input.bin", std::ios::in | std::ios::binary);
      myFile.read (buffer, 100);

      if (!myFile.read (buffer, 100)) {
        std::cout << "Could not open the required file\n";
      }
      else
      {
        for (int i = 0; i < 4; i++)
        {
          std::cout << "buffer[" << i << "] = " << static_cast<unsigned>(buffer[i]) << std::endl;
        }
        myFile.close();
      }
    return 0;
}

Currently I am printing just four bytes of data, and when I run it, I get this output:

buffer[0] = 0
buffer[1] = 24
buffer[2] = 0
buffer[3] = 0

Why is it not printing the value of 0f and just printing the value of 18 in index 1 whereas it is actually at index 6?

Answer 1

The problem is here

myFile.read (buffer, 100);

if (!myFile.read (buffer, 100)) {

where you read twice, and thus ignore the first 100 bytes (if there are more than 100 of them).

Remove the first read , or change the condition to if (!myFile)

Answer 2

You print the contents of the data as characters . And none of the first four bytes are really printable characters.

You need to print them as (unsigned) integers:

// Unsigned bytes to avoid possible sign extensions in conversions
unsigned char buffer[100];

...

// Convert the bytes to unsigned int for printing their numerical values
std::cout << "buffer[" << i << "] = " << static_cast<unsigned>(buffer[i]) << '\n';