String structure bug

[plaurenc]

Hello Rob,
Thank you for this superb library but I encounter a bug when I try to save a string type structure, I try to save a telephone number in international format for example "[phone]" the first character is always replaced by a bad one, if i decrease the size like "[phone]" does it work??
Thanks for your help

Pascal

here is the code from an example of the package.

Example 1 return

size: 20
write: 13105
read: 2947
temp: [phone]
hum: 53.10
pres: 1000.90
done...

Example 2 return

size: 20
write: 13105
read: 2947
temp: #32495030405
hum: 53.10
pres: 1000.90
done...

Test_1_I2C_eeprom_struct.zip
Test_2_I2C_eeprom_struct.zip

[Rob Tillaart]

Thanks for the issue, might take a few days before I can investigate.

[plaurenc]

Thanks a lot Rob, glad you're leaning to this problem 😊 Have a nice day Pascal Le mar. 28 mars 2023 à 11:02, Rob Tillaart ***@***.***> a écrit :

…

Thanks for the issue, might take a few days before I can investigate. — Reply to this email directly, view it on GitHub <#52 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ALRWOSUIXR5HGFJGNVGLOGLW6KSL5ANCNFSM6AAAAAAWKFZJUM> . You are receiving this because you authored the thread.Message ID: ***@***.***>

[Rob Tillaart]

Had a quick look and the problem is using a String in the struct.
Strings use dynamic memory and can allocate runtime new memory.

Assigning a new value to the String does not expand the struct. See this minimal sketch.

#include "Arduino.h"

struct
{
  String temperature;
  float humidity;
  float pressure;
} measurement;

void setup()
{
  Serial.begin(115200);
  while (!Serial);
  Serial.println(__FILE__);

  Serial.println(sizeof(measurement));
  measurement.temperature = "123456798123465789123456879X";
  Serial.println(sizeof(measurement));
  Serial.println(measurement.temperature);
  Serial.println(sizeof(measurement.temperature));
}

void loop()
{
}

output
14
14
123456798123465789123456879X
6

Size of the struct does not change after assigning the large String.

The size of 14 = 2x4 for the two floats and 6 bytes for the (reference to the) String.

Solution is to use a char array, something like

struct
{
  char temperature[32];
  float humidity;
  float pressure;
} m2;

this will allocate 32+4+4 = 40 bytes for the struct and should work.
Give it a try

[Rob Tillaart]

From the String class source code

protected:
	char *buffer;	        // the actual char array
	unsigned int capacity;  // the array length minus one (for the '\0')
	unsigned int len;       // the String length (not counting the '\0')

that makes up the 6 bytes allocated for the String.

[plaurenc]

If I declare char temperature[32]; I get a wrong return with C:\Users\plaur\Documents\Arduino\Test_2_I2C_eeprom_struct\Test_2_I2C_eeprom_struct.ino:51:27: error: incompatible types in assignment of 'int' to 'char [32]' 51 | measurement.temperature = "[phone]"; Sorry I am beginner I have some problem to translate String to char I try like this measurement.temperature = '[phone]' But no succes An idea how I can do ? Le mar. 28 mars 2023 à 11:37, Rob Tillaart ***@***.***> a écrit :

…

Had a quick look and the problem is using a String in the struct. Strings use dynamic memory and can allocate runtime new memory. Assigning a new value to the String does not expand the struct. See this minimal sketch. #include "Arduino.h" struct { String temperature; float humidity; float pressure; } measurement; void setup() { Serial.begin(115200); while (!Serial); Serial.println(__FILE__); Serial.println(sizeof(measurement)); measurement.temperature = "123456798123465789123456879X"; Serial.println(sizeof(measurement)); Serial.println(measurement.temperature); Serial.println(sizeof(measurement.temperature)); } void loop() { } output 14 14 123456798123465789123456879X 6 Size of the struct does not change after assigning the large String. The size of 14 = 2x4 for the two floats and 6 bytes for the (reference to the) String. Solution is to use a char array, something like struct { char temperature[32]; float humidity; float pressure; } m2; this will allocate 32+4+4 = 40 bytes for the struct and should work. Give it a try — Reply to this email directly, view it on GitHub <#52 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ALRWOSRAM7QTGRIAAJDRRB3W6KWOZANCNFSM6AAAAAAWKFZJUM> . You are receiving this because you authored the thread.Message ID: ***@***.***>

[Rob Tillaart]

Use strcpy(measurement.temperature, "12345")

[Rob Tillaart]

There is also a function String.toCharArray() something like that.

[plaurenc]

Cool, thanks! I will try with that 😉 Le mar. 28 mars 2023 à 12:40, Rob Tillaart ***@***.***> a écrit :

…

There is also a function String.toCharArray() something like that. — Reply to this email directly, view it on GitHub <#52 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ALRWOSRT57XZRYNLWH26YDDW6K5YHANCNFSM6AAAAAAWKFZJUM> . You are receiving this because you authored the thread.Message ID: ***@***.***>

[Rob Tillaart]

If it works you may close the issue

[plaurenc]

Ok Rob, I think I'll be able to manage, thank you for your prompt response, your help and also your precious library Le mar. 28 mars 2023 à 13:13, Rob Tillaart ***@***.***> a écrit :

…

If it works you may close the issue — Reply to this email directly, view it on GitHub <#52 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ALRWOSTDZS4EUGEDQMIUXFDW6LBUPANCNFSM6AAAAAAWKFZJUM> . You are receiving this because you authored the thread.Message ID: ***@***.***>

[Rob Tillaart]

Ok, otherwise please reopen the issue