Arduino - unable to connect to wifi - string

Question

I have this (partial) code, that is used to read the ssid and password from a text file on a SD card.
This data should then be used to connect to the local wifi. But it is unable to connect, and keeps saying "Establishing connection to WiFi..."
I also dont seem to be able to print what I have read from the SD card. Previously my readline function returned a string. That I was able to print properly and verified that the file is read as expected. Then, since wifi requires a Char* I changed the code to Char* and since then it didnt work anymore:
#include <SD.h>
#include <AccelStepper.h>
#include <MultiStepper.h>
#include <WiFi.h>
File myFile;
char* ssid;
char* password;
void setup() {
// put your setup code here, to run once:
pinMode(thetaPos, INPUT);
pinMode(rhoPos, INPUT);
Serial.begin(115200);
Serial.print("Initializing SD card...");
if (!SD.begin()) {
Serial.println("initialization failed!");
while (1);
}
Serial.println("initialization done.");
myFile = SD.open("/config.txt");
if (myFile) {
// read from the file until there's nothing else in it:
ssid = readLine();
password = readLine();
Serial.println(ssid);
Serial.println(password);
connectToNetwork();
// close the file:
myFile.close();
} else {
// file didn't open
}
}
void loop() {
}
char* readLine() {
char* received = "";
char ch;
while (myFile.available()) {
ch = myFile.read();
if (ch == '\n') {
return received;
} else {
received += ch;
}
}
return received;
}
void connectToNetwork() {
WiFi.begin(ssid, password);
while (WiFi.status() != WL_CONNECTED) {
delay(1000);
Serial.println("Establishing connection to WiFi..");
}
Serial.println("Connected to network");
}
what am I doing wrong?
this is the serial output:
Initializing SD card...initialization done.
ore calibration nvs commit failed(0x%x)
wdt_config->intr_handle)
Establishing connection to WiFi..
Establishing connection to WiFi..
Establishing connection to WiFi..
Establishing connection to WiFi..

Answer 1

Well, where is the error? This won't work as you hope:
char* readLine() {
char* received = ""; // poiner to \0 somewhere...
char ch;
while (myFile.available()) {
ch = myFile.read();
if (ch == '\n') {
return received;
} else {
received += ch; // move pointer to location ch bytes after...
}
}
return received;
}
You are utilizing pointer arithmetic - you are moving pointer around the memory and you are not storing anything anywhere. It's not String class that overloads += char and allows you to concatenate character to the end of it.
Basically you can use:
String readLine() {
String received;
while (myFile.available()) {
ch = myFile.read();
if (ch == '\n') {
return received;
} else {
received += ch;
}
}
return received;
}
and it'll work (althrough it's not a good idea to append character by character to the String - heap memory gets fragmented really fast by this approach)
To avoid other mistakes, usage is something like:
String ssid = readLine();
String pass = readLine();
Wifi.begin(ssid.c_str(), pass.c_str());
//// definitely do not do something like:
// Wifi.begin(readLine().c_str(), readLine().c_str()); // !!! WRONG !!!
//// as the order of executing parameters isn't specified (and in the GCC it's from the last to the first)