how to pass on some output from a c++ program to the shell so that it can be used in the shell - c++

Question

Is there any good way i can make some data created by my c++ program available to the shell after exiting the program?
I have a c++ program, inside which i have a string containing a path:
std::string path = "/home/some/path"
I want this path to be available after the c++ program exits main and i am returned to the shell, so that i can use that path (e.g. cd to that path).
I have considered/tried the following approaches:
I tried making an environment variable in c++ program using setenv(). However the environment variable only exists while in the c++ program, and it is apparently not possible to make those changes visible in the shell after exiting the program.
(considered) writing the path to a temporary file, so that a bash script could later access the details of the path from it. However i have read many suggestions to not do that due to security vulnerabilities.
I tried calling the bash script from within the c++ program, using system(). This does not work if i try to cd to that directory (exiting the program will keep me in the same directory as before).
I figure that if i am desperate, i could have my program cout the path, and use the solutions as described here:
$ ./program | tee output.txt
Then the path is stored inside the file. This works technically, but has the undesirable effect of creating a file and printing the path to the screen, and is basically creating a temporary file.
another option to, again, cout in my program, and use command substitution. running in the shell
$ var=$(./program)
storing the path in var. This didnt work because my program does many things including requiring user input before calling
std::cout<< path << std::endl;.
Particularly, i have observed this approach to not display a curses window, which is required for the program.
the only solution that has worked is piping the output to tee.

Answer 1

Environment variables are only an input, they cannot be used to return any information from a program.
You are already using std::cin and std::cout for user input, and std::cerr should be reserved for error messages. However, you can have the shell open more filedescriptors, and have your program write to those. However, doing this with pure C++ is not possible. But if you don't mind using POSIX C functions:
#include <cstdio>
int main() {
FILE *f = fdopen(3, "w");
fprintf(f, "some path\n");
}
And then use it like so:
./program 3> output.txt
This of course creates an undesirable file. I don't think there is any way to store the output from an extra filedescriptor directly to a variable in bash. However, you could create a temporary file inside /dev/shm, so it will never be written to disk, or create a FIFO object and redirect the output from the program to the FIFO, and then read it back. For some examples of how to do this, see this question.

Answer 2

You could write the output that you want the user to see to stderr instead of stdout. Only output what you need your shell script to see to stdout:
#include <iostream>
int main() {
std::clog << "Enter data: "; // clog prints to stderr like cerr
std::string line;
std::getline(std::cin, line);
std::cout << line << '\n';
}
Then this will work:
var=$(./program)