Extracting a specific sequence of characters from an array

Question

I have a character array called storebuffer that contains data from a POST submission and its in the format ssid=abcdef&pswd=ghijk. I wanted to extract everything after ssid= into one array called acqSSID and the portion after &pswd= into another array called acqPaswd. I tried using this but it does not seem to be working. MAX_STORE_BUFFER_LEN is 255. Can anyone help?

int ctr = 0;
for (ctr = 5; ctr < MAX_STORE_BUFFER_LEN; ctr++)
{
 if ( (storebuffer[ctr] == '&') && (storebuffer[ctr+1] == 'p') && (storebuffer[ctr+2] == 's') && (storebuffer[ctr+3] == 'w') && (storebuffer[ctr+4] == 'd') && (storebuffer[ctr+5] == '=') )
 {
 break;
 }
 acqSSID[ctr] = storebuffer[ctr];
}
Serial.print("acqSSID: ");
Serial.println(acqSSID);
Serial.print("ctr: ");
Serial.println(ctr);

Answer 1

You can simply chop it up in place without requiring more than a few extra bytes of RAM using strtok():

char storebuffer[] = "ssid=abcdef&pswd=ghijk";
// Slice it into two parts around the &:
char *lefthalf = strtok(storebuffer, "&");
if (lefthalf != NULL) { // We found a & and split the string OK
 char *righthalf = strtok(NULL, "&");
 // Now you can slice each half around the =
 char *ssidtag = strtok(lefthalf, "=");
 char *ssid = strtok(NULL, "=");
 char *pswdtag = strtok(righthalf, "=");
 char *pswdtag = strtok(NULL, "=");
 Serial.print("SSID: ");
 Serial.println(ssid);
 Serial.print("Password: ");
 Serial.println(pswd);
}

The existing string gets chopped up and the pointers point to different places:

ssid0円abcdef0円pswd0円ghijk
^ ^ ^ ^
1 2 3 4
1: ssidtag
2: ssid
3: pswdtag
4: pswd

Answer 2

Rather than acqSSID[ctr] = storebuffer[ctr];, say (eg) acqSSID[ctr-5] = storebuffer[ctr];. Also, after the break but before printing acqSSID, say acqSSID[ctr-5] = 0; to terminate the string.

Note, rather than coding a literal 5, you might say enum { acqOffset=5 }; up front, and subsequently use acqOffset in place of the literal.