Reading strings from structures in PROGMEM using a loop

Found a solution, see my comment below!

I am trying to read data which is placed in structures and stored in the flash memory of an Arduino Mega (ATmega 2560) using PROGMEM. The structure objects manufacturer_1 and manufacturer_2 are accessed with pointers.

Due to size of the sketch; I decided to create a (relative) small example which illustrates the problem. The following code shows how I define the structures and data.

typedef struct
{
   char info[20];
} manufacturer_def;

typedef struct
{
   unsigned int totalManufacturers;
   const manufacturer_def* manufacturer[2];
} data_def;

const manufacturer_def manufacturer_1 PROGMEM =
{
   "Manufacturer 1"
};

const manufacturer_def manufacturer_2 PROGMEM =
{
   "Manufacturer 2"
};

const data_def data PROGMEM =
{
  2,
  {
    &manufacturer_1,
    &manufacturer_2
  }
};

void setup() 
{
  // Serial monitor setup
  Serial.begin(115200);   // Begin serial monitor
}

void loop() 
{
   mainMenu();
}

The problem!

I would like to fill an array with strings using a loop. The following code is not working properly:

void mainMenu()
{
   unsigned int i = 0;

   unsigned int totalMenuItems = pgm_read_word(&data.totalManufacturers);
   String menuItems[totalMenuItems];

   char str_buf[20];

   // Create array with items for menu
   for (i = 0; i < totalMenuItems; i++)
   {
     strcpy_P(str_buf, data.manufacturer[i]->info);
     menuItems[i] = str_buf;
     Serial.println(menuItems[i]);
   }
 }

Output (section):

p�









p�

Strangely, when I place the strcpy_P command outside the loop and specify the iteration variable by hand it works:

void mainMenu()
{
  unsigned int i = 0;

  unsigned int totalMenuItems = pgm_read_word(&data.totalManufacturers);
  String menuItems[totalMenuItems];

  char str_buf[20];

  strcpy_P(str_buf, data.manufacturer[0]->info);
  menuItems[0] = str_buf;
  strcpy_P(str_buf, data.manufacturer[1]->info);
  menuItems[1] = str_buf;

  // Create array with items for menu
  for (i = 0; i < totalMenuItems; i++)
  {
    Serial.println(menuItems[i]);
  }
}

Output:

Manufacturer 1
Manufacturer 2

Why is this happening?