The use of "if (strcmp(URL, "/") == 0)" in Arduino network sketches

StackOverflow https://stackoverflow.com/questions/23200430

  •  07-07-2023
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سؤال

I'm trying to understand the "if (strcmp(URL, "/") == 0)" line in the Arduino sketch below (see the sendMyPage function about halfway down): 

#include <WiServer.h>

#define WIRELESS_MODE_INFRA 1
#define WIRELESS_MODE_ADHOC 2
#define AREF_VOLTAGE 5
const int tmpPin = A0;
int tmpReading = 0;
// Wireless configuration parameters ----------------------------------------
unsigned char local_ip[] = {192,168,31,199}; // IP address of WiShield
unsigned char gateway_ip[] = {192,168,1,1}; // router or gateway IP address
unsigned char subnet_mask[] = {255,255,255,0}; // subnet mask for the local network
const prog_char ssid[] PROGMEM = {"MERCURY_7F3F70"}; // max 32 bytes

unsigned char security_type = 3; // 0 - open; 1 - WEP; 2 - WPA; 3 - WPA2

// WPA/WPA2 passphrase
const prog_char security_passphrase[] PROGMEM = {"11163127"}; // max 64 characters

// WEP 128-bit keys
// sample HEX keys
prog_uchar wep_keys[] PROGMEM = { 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, // Key 0
 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // Key 1
 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // Key 2
 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 // Key 3
};

// setup the wireless mode
// infrastructure - connect to AP
// adhoc - connect to another WiFi device
unsigned char wireless_mode = WIRELESS_MODE_INFRA;

unsigned char ssid_len;
unsigned char security_passphrase_len;
// End of wireless configuration parameters ----------------------------------------
float testTmp (void){
  tmpReading = analogRead (tmpPin);
  float voltage = tmpReading * AREF_VOLTAGE;
  voltage /= 1023;
  float tmpC = (voltage - 0.5) * 100;
  return tmpC;
}

// This is our page serving function that generates web pages
**boolean sendMyPage(char* URL)** {

    // Check if the requested URL matches "/"
    **if (strcmp(URL, "/") == 0) {**
        // Use WiServer's print and println functions to write out the page content
        float tmpC = testTmp ();
        WiServer.print("<html>");
//        WiServer.print("Hello World!");
        WiServer.print(tmpC);
        WiServer.print("</html>");

        // URL was recognized
        return true;
    }
    // URL not found
    return false;
}


void setup() {
  // Initialize WiServer and have it use the sendMyPage function to serve pages
  WiServer.init(sendMyPage);

  // Enable Serial output and ask WiServer to generate log messages (optional)
  Serial.begin(57600);
  WiServer.enableVerboseMode(true);
}

void loop(){

  // Run WiServer
  WiServer.server_task();

  delay(10);
}

It seems that the function accepts a URL as an argument, and sends data to the page using WiSever.print if the URL is valid. But how does 'if (strcmp(URL, "/") == 0)' determine if the URL is good?

I've seen this kind of check before, but don't understand how it works.

Thanks!

هل كانت مفيدة؟

المحلول

The line: 

if (strcmp(URL, "/") == 0) {

Is testing to see if the string URL exactly matches the string literal "/". If so, it returns 0.

Note, if you wanted to test to see if the string URL contained "/", then use: 

 if (strstr(URL, "/") != NULL) {

Regarding But how does 'if (strcmp(URL, "/") == 0)' determine if the URL is good?
It does not. More would be needed than a single character to determine if URL was good, it appears that the comment, as written, is not really expressing what that code block actually does.

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