How to use esp8266WiFi Library GET request to obtain info from a website

Question

I'm working on the ESP8266 ESP-01 WiFi module programmed with Arduino IDE to send GET request to a URL and read the contents.
Trying to modify the below code which uses the ESP8266WiFi library, I'm not clear what to replace for host. Should i put my URL in host or something else? Also how to edit the line.

client.print(String("GET ") + url + " HTTP/1.1\r\n" +
           "Host: " + host + "\r\n" + 
           "Connection: close\r\n\r\n");

#include <ESP8266WiFi.h>

const char* ssid     = "your-ssid";
const char* password = "your-password";

const char* host = "data.sparkfun.com";
const char* streamId   = "....................";
const char* privateKey = "....................";

void setup() {
  Serial.begin(115200);
  delay(10);

  // We start by connecting to a WiFi network

  Serial.println();
  Serial.println();
  Serial.print("Connecting to ");
  Serial.println(ssid);

  WiFi.begin(ssid, password);

  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }

  Serial.println("");
  Serial.println("WiFi connected");  
  Serial.println("IP address: ");
  Serial.println(WiFi.localIP());
}

int value = 0;

void loop() {
  delay(5000);
  ++value;

  Serial.print("connecting to ");
  Serial.println(host);

  // Use WiFiClient class to create TCP connections
  WiFiClient client;
  const int httpPort = 80;
  if (!client.connect(host, httpPort)) {
    Serial.println("connection failed");
    return;
  }

  // We now create a URI for the request
  String url = "/input/";
  url += streamId;
  url += "?private_key=";
  url += privateKey;
  url += "&value=";
  url += value;

  Serial.print("Requesting URL: ");
  Serial.println(url);

  // This will send the request to the server
  client.print(String("GET ") + url + " HTTP/1.1\r\n" +
               "Host: " + host + "\r\n" + 
               "Connection: close\r\n\r\n");
  unsigned long timeout = millis();
  while (client.available() == 0) {
    if (millis() - timeout > 5000) {
      Serial.println(">>> Client Timeout !");
      client.stop();
      return;
    }
  }

  // Read all the lines of the reply from server and print them to Serial
  while(client.available()){
    String line = client.readStringUntil('\r');
    Serial.print(line);
  }

  Serial.println();
  Serial.println("closing connection");
}

Answer 1

Your line client.print(String("GET ") + url + " HTTP/1.1\r\n" + "Host: " + host + "\r\n" + "Connection: close\r\n\r\n"); is OK. You don't need to change it.

For host you have to provide domain name or IP address. Eg. const char* host = "example.com";.

Example

If you want to get http://stackoverflow.com/questions/39707504/how-to-use-esp8266wifi-library-get-request-to-obtain-info-from-a-website you should have:

const char* host = "stackoverflow.com";
String url = "/questions/39707504/how-to-use-esp8266wifi-library-get-request-to-obtain-info-from-a-website";