Change a constant variable without rebuilding C++

Question

I've developed a c++ project with visual studio 2015. The output of my project is a single executable that must have a unique ID for every client and this ID must be accessible inside the code. A simple approach is to just define a constant variable inside the code and change its value for every client and build it many times but I have a Linux server and I'm not sure I can build it simply because I've used many Winapi libraries. I was thinking that maybe there is another way to change or add some constant value to the output like manipulating the executable. For example:

#include <string>
#include <iostream>
#include <Windows.h>


const std::string ID = "some unique ID";

int main() {
    std::cout << "Your ID: " << ID << std::endl;
    getchar();
    return(0);
}

Answer 1

It seems that there are only two approaches. One is just building the project inside a Linux environment which is a better method but must be used some tools like Mono XBuild link here. Another option which may be simpler is just open the binary file and manipulate the specific string. As @aloMalbarez comment Here is a simple script based on this. Suppose this example: (I used 50 ms as a fixed length for my ID)

#include <string>
#include <iostream>
#include <Windows.h>

#define ID "mmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm"


using namespace std;

int main() {
    cout << "Your ID: " << ID << "\nlen:" << strlen(ID) <<  endl;
    getchar();
    return(0);
}

After generating the executable use the following script to create output. I'm not a Linux guy so you can help me improve this. ./build.sh input.exe output.exe "myfixedID"

#!/bin/bash
# build.sh input_file output_file <ID>


input_file=$1
output_file=$2
ID=$3


if [ -z "$1" ] || [ -z "$2" ] || [ -z "$3" ]; then
  echo "wrong parameters"
  echo "build.sh input_file output_file <ID>"
  exit 1
fi

# use fixed string (ID) in the source file
# this creates 50 of "m"s
search_value=$(printf 'm%.0s' {1..50})

extension=".back"
temp_file="$input_file$extension"
tmpstring_file="./tmp"
null_termin='\0'


echo "copying the original file..."
yes | cp -rf $input_file $temp_file

address=$(strings -t d $temp_file | grep $search_value | grep -o '[0-9]*')

echo "Address:"
echo $address
if ! [[ $address =~ ^[0-9]+$ ]]; then
  echo "cannot find valid ID in executable"
  echo "removing temps"
  rm $temp_file
  exit 1
fi


# make the tempstring file
printf "$ID$null_termin" > $tmpstring_file

dd if=$tmpstring_file of=$temp_file obs=1 seek=$address conv=notrunc

echo "make new file"
yes | cp -rf $temp_file $output_file

echo "removing temps"

rm $temp_file $tmpstring_file

echo "Done!"

Answer 2

In init function of your program. Generate a unique id based of SHA-1 hash of current time, IP address, username (same more). you can do whatever you want to do in that program afterward (i.e save in database). Will that work ?

Answer 3

A Constant is not a Variable, they are opposite types. A Constant is an element that is assigned a particular value that does not change, thus the word constant, unchanging.
A Variable on the other hand is an element that is stored in memory as a changeable value, as your program runs, the VARIABLE can change it's current value.

In Visual Studio, you can create a configuration file that passes set values to your program, these values are variable, and can be changed programmatically and manually. But, as you stated you do not want a separate file to look up information from.

If you want to track users by their Unique ID, then you must have a database somewhere that can record new users and issue a unique ID, or, you can create a unique ID based on the date and time that the account is created, if you are creating a unique executable for each one, the date/time information is included in the file creation information, so you would simply use that, since every file is created at a unique date/time, that would always indicate the ID. You could keep the same name for each file, or incorporate the date/time into the filename, like myPro20180522183231.exe which would be year 2018 month 05 day 22 hour 18 minutes 32 seconds 31 and this could be confirmed through the date/time information of the file creation data.