how to read binary file content as strings? - c++

Question

I need to read 16 bits from the binary file as std::string or char *. For example, a binary file contains 89 ab cd ef, and I want to be able to extract them as std::strings or char *. I have tried the following code:
ifstream *p = new ifstream();
char *buffer;
p->seekg(address, ios::beg);
buffer = new char[16];
memset(buffer, 0, 16);
p->read(buffer, 16);
When I try to std::cout the buffer, nothing appeared. How can I read these characters in the binary file?
EDIT: I was looking for the buffer to be a int type such as "0x89abcdef". Is it possible to achieve?

Answer 1

Something like:
#include <string>
#include <iostream>
#include <fstream>
#include <iomanip>
int main()
{
if (ifstream input("filename"))
{
std::string s(2 /*bytes*/, '\0' /*initial content - irrelevant*/);
if (input.read(&s[0], 2 /*bytes*/))
std::cout << "SUCCESS: [0] " << std::hex << (int)s[0] << " [1] " << (int)s[1] << '\n';
else
std::cerr << "Couldn't read from file\n";
}
else
std::cerr << "Couldn't open file\n";
}

Answer 2

You can't read a binary stream as though it were text.
You can, of course, read as binary (by using "file.read()" and "file.write()" methods on your stream object). Just like what you're doing now :)
You can also convert binary to text: "convert to hex text string" and "uuencode base 64" are two common ways to do this.

Answer 3

You'll want to read the bytes as numbers (of type long long probably).
Then you can print those using formatting specifiers like this:
#include <iostream>
#include <iomanip>
int main()
{
using namespace std;
int x = 2;
int y = 255;
cout << showbase // show the 0x prefix
<< internal // fill between the prefix and the number
<< setfill('0'); // fill with 0s
cout << hex << setw(4) << x << dec << " = " << setw(3) << x << endl;
cout << hex << setw(4) << y << dec << " = " << setw(3) << y << endl;
return 0;
}