DHT11 sensor and internet communication

[adremasu]

Hi, I'm trying to create a log of registered temperatures using arduino nano, temperature/moisture sensor DHT11 and Ethernet shield HR911105A.
I put together 2 examples of sketches from the EtherCard and the DHT Libraries.
So combining them I got this piece of code:

// Demo using DHCP and DNS to perform a web client request.
// 2011-06-08 <jc@wippler.nl>
//
// License: GPLv2
#include "DHT.h"
#include <EtherCard.h>

#define DHTPIN 9    
#define DHTTYPE DHT11   // DHT 11

// ethernet interface mac address, must be unique on the LAN
static byte mymac[] = { 0x74,0x69,0x69,0x2D,0x30,0x31 };
DHT dht(DHTPIN, DHTTYPE);

byte Ethernet::buffer[700];
static uint32_t timer;
const char website[] PROGMEM = "www.example.com";
const  char* webpage = "temp_log.php?temp=";
// called when the client request is complete
static void my_callback (byte status, word off, word len) {
  Serial.println(">>>");
  Ethernet::buffer[off+300] = 40;
  Serial.print((const char*) Ethernet::buffer + off);
  Serial.println("...");
}

void setup () {
  dht.begin();
  Serial.begin(57600);
  Serial.println(F("\n[webClient]"));
  ether.printIp("DHCP server: ", ether.dhcpip);
  // Change 'SS' to your Slave Select pin, if you arn't using the default pin
  if (ether.begin(sizeof Ethernet::buffer, mymac, SS) == 0)
    Serial.println(F("Failed to access Ethernet controller"));
  if (!ether.dhcpSetup())
    Serial.println(F("DHCP failed"));
  ether.printIp("IP:  ", ether.myip);
  ether.printIp("GW:  ", ether.gwip);
  ether.printIp("DNS: ", ether.dnsip);

#if 1
  // use DNS to resolve the website's IP address
  if (!ether.dnsLookup(website))
    Serial.println("DNS failed");
#elif 2
  // if website is a string containing an IP address instead of a domain name,
  // then use it directly. Note: the string can not be in PROGMEM.
  char websiteIP[] = "142.250.184.68";
  ether.parseIp(ether.hisip, websiteIP);
#else
  // or provide a numeric IP address instead of a string
  byte hisip[] = { 142,250,184,68 };
  ether.copyIp(ether.hisip, hisip);
#endif

  ether.printIp("SRV: ", ether.hisip);
}

void loop () {

  char* finstr;
  finstr = malloc(strlen(webpage)+1+5);
  float h = dht.readHumidity();
  float t = dht.readTemperature();
  ether.packetLoop(ether.packetReceive());
  if (millis() > timer) {

    // Check if any reads failed and exit early (to try again).
    if (isnan(h) || isnan(t)) {
      Serial.println(F("Failed to read from DHT sensor!"));
      return;
    }
    timer = millis() + 5*60UL*1000;
    Serial.print("<<< REQ ");
    Serial.println(t);
    char result[8]; // Buffer big enough for 7-character float
    dtostrf(t, 3, 2, result); // Leave room for too large numbers!
    
    strcpy(finstr, webpage); /* copy name into the new var */
    strcat(finstr, result); /* add the extension */
    //Serial.println(finstr);
    ether.browseUrl(PSTR("/"), finstr, website, my_callback);
    
  }
}

Everything works fine when I upload the sketch, but after a couple of loop, it just stop woring; do you have any idea why?

[pylon]

@adremasu

  finstr = malloc(strlen(webpage)+1+5);

In every loop you allocate memory but you never return it.
As the size is constant, allocate it on the stack (local variable) and don't use malloc() at all.