Reading a .dat File in C++ gives Symbols instead of Numbers

Question

I am trying to open a.dat binary file in C++ as an exercise, however when I try to print out the contents of the file, I receive symbols instead of numbers.

Here is the code on how I read the.dat file:

int main() {
    errno_t status;
    std::FILE *input_file;

    status = fopen_s(&input_file, filename, "rb");
    
    if (status == 0) {
        std::string content;

        std::fseek(input_file, 0, SEEK_END);
        content.resize(std::ftell(input_file));
        std::rewind(input_file);
        std::fread(&content[0], 1, content.size(), input_file);
        std::fclose(input_file);

        for (int i = 0; i < 10; i++) {
            std::cout << content[i];
        }
    }

    return 0;
}

I also tried it using C++ fstream .

int main() {
    std::ifstream input_file(filename, std::ios::in | std::ios::binary);
    if (input_file) {
        std::string content;

        input_file.seekg(0, std::ios::end);
        content.resize(input_file.tellg());
        input_file.seekg(0, std::ios::beg);
        input_file.read(&content[0], contents.size());
        input_file.close();

        for (int i = 0; i < 10; i++) {
            std::cout << content[i];
        }
    }

    return 0;
}

When I try to print the content of content , it returns ⁿ\|Cⁿ\|Cⁿ\ (for the first 10 elements), which corresponds to the first 10 bytes of the file: fc 5c 7c 43 fc 5c 7c 43 fc 5c (according to a Hex Editor).

I could easily open the file in Python by using

data = numpy.fromfile(filename, "=f")

and returns the following (which I expect),

array([252.36322, 252.36322, 252.36322, ..., 239.38304, 239.38304,
       239.38304], dtype=float32)

I also looked into the number of bytes each element should have using Python, and it returned 4, which matches with the output of std::ftell(input_file) (the file should have 36 million points), but I tried changing 1 to 4 in the line std::fread(&content[0], 1, content.size(), input_file);and it returns an empty content . Also, as far as I know, the file doesn't contain any headers, so I think the data should begin at the very first bit.

So, how could I open and read the.dat file in C++ so that it returns the same value as Python?

Thank you in advance.

Answer 1

The loop

for (int i = 0; i < 10; i++) {
    std::cout << content[i];
}

is printing the data by interpreting the data as representing the character codes of invidual characters. However, this is not what the data represents. The data actually represents single-precision floating-point numbers. Therefore, you should interpret it as such:

for (int i = 0; i < 10; i++) {
    float f;
    std::memcpy( &f, content.data() + i * sizeof f, sizeof f );
    std::cout << f << '\n';
}

Note that you must #include <cstring> in order to use std::memcpy .

Answer 2

You should use C++'s fstream instead of C functions as such:

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

int main() 
{
    std::ifstream in("batFile.bat");

    if (in) 
    {
        std::string content;

        std::string line;
        while (std::getline(in, line))
        {
            content += line + '\n';
        }
        std::cout << content;
    }

    return 0;
}

batFile.bat

12
12
13
13

output

12
12
13
13

As you can see this code works perfectly fine, you may modify it as per your requirements:)