Hi all,
I am having a very weird problem trying to get Preferences.getBytes to work. My key names are labelled as "001", "002", "003" ... up to "200" and I am using a character array(char myKey[3] - declared as a global variable) to dynamically assign the key names. And I have written a simple function that takes in an integer and converts it to the correct character array format. For example:
when I call the function convertCharArray(2), it sets myKey[0] ='0', myKey[1]='0' and myKey[2]='2'
Writing into the preference file looks something like this:
convertCharArray(2);
preferences.putBytes(myKey, myData, 6);
And this works perfectly fine.
However, when I try to read back the data using the following, it doesn't work:
convertCharArray(2);
preferences.getBytes(myKey, myData, 6);
The preferences.getByes function should return back 6 but it returns back 0. If I were to provide a constant string into the preferences.getBytes function, then everything works fine:
preferences.getBytes("002", myData, 6);
The preferences.getBytes function has the following function prototype:
size_t getBytes(const char* key, void * buf, size_t len);
The key name is a const char* I wonder if I did anything wrong. But writing works! Just not reading back.
Hope someone can advise. Thanks in advance!
Dynamically assigning Preferences name gives problems when reading back
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- Posts: 826
- Joined: Mon Jul 22, 2019 3:20 pm
Re: Dynamically assigning Preferences name gives problems when reading back
Nobody is going to be able to debug code that you don't include. If you are just fishing for someone to do your homework, here you go.
Code: Select all
#include <Preferences.h>
Preferences prefs;
void setup() {
Serial.begin(115200);
prefs.begin("sequence");
for (int x=0; x<50; x++) {
char num1[6];
snprintf(num1, 6, "%05d", x);
prefs.putBytes(String(x).c_str(), num1, 6);
}
}
void loop() {
char randtxt[6];
int randseq = random(50);
prefs.getBytes(String(randseq).c_str(), randtxt, 6);
Serial.printf("seq: %d\ttxt: %s\n", randseq, randtxt);
delay(5000);
}
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