Timing duration between two events - c++

Question

I want to compute the time between when I transmit and when I receive. My timer will start counting once I start transmitting then the timer will stop once I receive a response. I'm using C++ on my arduino uno. Base on my code I'm just measuring the delay, Which is not good. what I'm trying to measure is the elapsed time between i transmit and received. I hope you can help me.
output image
My code
#include <VirtualWire.h>
const int transmit_pin = 12;
const int receive_pin = 11;
char *controller;
unsigned long start, finished, elapsed;
void setup() {
//receiver settings
Serial.begin(9600); // Debugging only
vw_set_rx_pin(11);
vw_rx_start();
//transmitter settings
pinMode(13, OUTPUT);
vw_set_ptt_inverted(true);
vw_set_tx_pin(12);
vw_setup(1000); // speed of data transfer Kbps
}
void displayResult()
{
float h,m,s,ms;
unsigned long over;
elapsed=finished-start;
h=int(elapsed/3600000);
over=elapsed%3600000;
m=int(over/60000);
over=over%60000;
s=int(over/1000);
ms=over%1000;
Serial.print("Raw elapsed time: ");
Serial.println(elapsed);
Serial.print("Elapsed time: ");
Serial.print(h,0);
Serial.print("h ");
Serial.print(m,0);
Serial.print("m ");
Serial.print(s,0);
Serial.print("s ");
Serial.print(ms,0);
Serial.println("ms");
Serial.println();
}
void loop() {
//Transmitter
digitalWrite(13, 1);
controller = "1";
vw_send((uint8_t *)controller, strlen(controller));
vw_wait_tx(); //Wait until the whole message is go
start=millis();
delay(1000); // for debounce
Serial.println("Started...");
//Receiver
uint8_t buf[VW_MAX_MESSAGE_LEN];
uint8_t buflen = VW_MAX_MESSAGE_LEN;
if (vw_get_message(buf, &buflen)) { // Non-blocking
digitalWrite(13, 0); //Flash a light to show received good
for(int i = 0;i < buflen;i++) {
if (buf[i] == '2')
{
finished=millis();
delay(1000); // for debounce
displayResult();
elapsed=finished-start;
Serial.print(start);
Serial.println(" milliseconds start");
Serial.print(finished);
Serial.println(" milliseconds finished");
Serial.print(elapsed);
Serial.println(" milliseconds elapsed");
Serial.println();
}
}
}
}

Answer 1

You say "Base on my code I'm just measuring the delay, Which is not good."
Ok, well:
start=millis();
delay(1000); // for debounce
Well, if you don't want to include the delay in your elapsed time, then take the start time after the delay(), not before.
This seems to be too obvious, so I suspect that you're really asking about something else. You need to show the output you're getting, why you think it's wrong, and what output you expect to get, instead.

Answer 2

Every thing happens during your delay period (the 1000ms delay). The message is received and stored in the buffer waiting for you to read it while you're in the delay. You're now measuring the execution time of a couple of lines of code and that takes less than a millisecond that is why you are getting the 0ms time.