I am trying to read a file which contains bytes into a hex string.
std::ifstream infile("data.txt", std::ios_base::binary);
int length = 10;
char char_arr[length];
for (int i=0; i<length; i++)
{
infile.get(char_arr[i]);
}
std::string hex_data(char_arr);
However the hex_data does not look like a hex string. Is there a way to convert the bytes to a hex string during reading?
You are reading in raw bytes and storing them as-is into your std::string. If you want the std::string to be hex formatted, you need to handle that formatting yourself, eg:
#include <fstream>
#include <sstream>
#include <iomanip>
#include <string>
std::ifstream infile("data.txt", std::ios_base::binary);
const int length = 10;
unsigned char bytes[length];
if (infile.read(reinterpret_cast<char*>(bytes), length)) {
size_t numRead = infile.gcount();
std::ostringstream oss;
for(size_t i = 0; i < numRead; ++i) {
oss << std::hex << std::setw(2) << std::setfill('0') << static_cast<unsigned short>(bytes[i]);
}
std::string hex_data = oss.str();
...
}
use std::stringstream object
std::stringstream stream;
stream << std::hex << static_cast<int>( your_char);
std::string result( stream.str() );
std::ostringstream instead for output-only operations like this. But more important, if the char is signed, and its high bit is 1, this will cause the int to sign-extend, producing unwanted results. For example, 0x80 will be printed as ff80. Use unsigned chars instead to avoid that.static_cast<unsigned short>(char(0x80)) but the result also ff80 I had to go through a double conversion to break the effect of the strong point bit: static_cast<int>(static_cast<unsigned char>(char(0x80)))char to an unsigned short performs sign-extension, because the char is promoted to int first, then the result is casted. See Standard C++ Behavior of Signed Char to Unsigned Int Conversion. But note that in my code example, the data starts out as unsigned char to begin with, so the bytes don't need an extra cast to unsigned before then casted to unsigned short.
std::stringconstructor that you are using requires a null terminatedchararray.int length = 10; char char_arr[length];is not standard C++, see Why aren't variable-length arrays part of the C++ standard?. Either makelengthconst, or else usenew[]or betterstd::vector.char*by itself. There is another constructor that accepts a lengthstd::string. But that is pretty moot in this case.