Progress bar during operation in console application - c++

Question

I started working on an encryption application but I seemed to greatly over think how I would get it to show a progress bar as it worked.
the task is simple lSize is the total size od the files being encrypted.
With the following loop in C++
//********** Open file **********
FILE * inFile = fopen (argv[1], "rb");
fseek(inFile , 0 , SEEK_END);
unsigned long lSize = ftell(inFile);
rewind(inFile);
unsigned char *text = (unsigned char*) malloc (sizeof(unsigned char)*lSize);
fread(text, 1, lSize, inFile);
fclose(inFile);
//*********** Encypt ************
unsigned char aesKey[32] = {
/* Hiding this for now */
};
unsigned char *buf;
aes256_context ctx;
aes256_init(&ctx, aesKey);
for (unsigned long i = 0; i < lSize/16; i++) {
buf = text + (i * 16);
aes256_decrypt_ecb(&ctx, buf);
}
aes256_done(&ctx);
//******************************************************
I was wondering how I could display the progress for the for loop while it works.
I know I need to calculate how much is done so far but I do not know how to do so.

Answer 1

What you need is multi-threading. Here is some sample source for a progress bar (from: http://www.cplusplus.com/reference/future/future/)
#include <iostream> // std::cout
#include <future> // std::async, std::future
#include <chrono> // std::chrono::milliseconds
// a non-optimized way of checking for prime numbers:
bool is_prime (int x) {
for (int i=2; i<x; ++i) if (x%i==0) return false;
return true;
}
int main ()
{
// call function asynchronously:
std::future<bool> fut = std::async (is_prime,444444443);
// do something while waiting for function to set future:
std::cout << "checking, please wait";
std::chrono::milliseconds span (100);
while (fut.wait_for(span)==std::future_status::timeout)
std::cout << '.';
bool x = fut.get(); // retrieve return value
std::cout << "\n444444443 " << (x?"is":"is not") << " prime.\n";
return 0;
}