Compiler throws "Invalid initializer" when writing char const*

Question

I'm new to C programming so please help a fella out. When compiling I'm getting a "invalid initializer" problem.This is the relevant code.

void lcd_writePString(char const* string) {
  char c;
  while ((c = (char)pgm_read_byte(string++)))
  lcd_writeChar(c);
}

void os_errorPStr(char const* str) {
  SREG &= 0b10111111; //Interrupts global deaktivieren
  lcd_clear();
  lcd_writePString(PSTR(str)); //THIS IS WHERE THE COMPILER THROWS OUT THE ERROR
  while (os_getInput()!=0b10000001){
    os_waitForInput();
  }
  lcd_clear();
  SREG |= 0b01000000;
 }

So why does my compiler throw out the error "invalid initializer"? The PSTR thing writes the string onto the flash memory of my micro controller.

This is what PSTR does:

 /** \ingroup avr_pgmspace
     \def PSTR(s)

    Used to declare a static pointer to a string in program space. */
 # define PSTR(s) ((const PROGMEM char *)(s))
 #else  /* !DOXYGEN */
 /* The real thing. */
 # define PSTR(s) (__extension__({static const char __c[] PROGMEM = (s); &__c[0];}))
 #endif /* DOXYGEN */

Answer 1

lcd_writePString expects a char const* yet you cast the parameter to const PROGMEM char * through some obscure macro. Either don't cast it to this type or change the prototype of lcd_writePString.