[solved] sizeof array is shrinking in function

Projects Programming
1

4 hours spent cant figure out why its shrinking its size.

#include <avr/pgmspace.h>
#include <stdio.h>
#include <stdlib.h>
void check_internet(const char destination[]);
void ping_module(const byte module);
#define ip_address_size 16

const char M_IP[] PROGMEM="192.168.4.";

void setup() {
  // put your setup code here, to run once:
Serial.begin(9600);

}

void loop() {
 ping_module(5);
 delay(2000);
  // put your main code here, to run repeatedly:

}

void ping_module(const byte module) {
  
  const byte base = 10;
  
  if (!module) return;
  
  char _buffer[3];
  
  memset(_buffer, '\0', sizeof(_buffer));
  
  char module_ip_temp[ip_address_size];
  
  memset(module_ip_temp, '\0', sizeof(module_ip_temp));

  itoa(module, _buffer, base);
  
  for (byte i = 0; i < strlen_P(M_IP); i++) module_ip_temp[i] = pgm_read_byte_near(M_IP + i);
    
  strcat(module_ip_temp, _buffer);

  char module_ip[strlen(module_ip_temp) + 1];

  memset(module_ip, '\0', sizeof(module_ip));

  strcpy(module_ip, module_ip_temp);

  Serial.print(F("strlen of module_ip="));
  Serial.println(strlen(module_ip));
  
  for(byte i=0;i<strlen(module_ip);i++){
    Serial.print(module_ip[i]);
    Serial.print('\t');
    Serial.println(i);
  }
  Serial.print(F("size of destination before calling function"));
  Serial.println((unsigned int)(sizeof(module_ip)/sizeof(module_ip[0])));
  check_internet(module_ip);
return;
}

void check_internet(const char destination[]) {

Serial.print(F("size of destination in function="));
Serial.println((unsigned int)(sizeof(destination)/(sizeof(destination[0]))));
return ;

}

output:

strlen of module_ip=11
1	0
9	1
2	2
.	3
1	4
6	5
8	6
.	7
4	8
.	9
5	10
size of destination before calling function12
size of destination in function=2

thanks

3

Thanks a lot Delta_G ! +1

4

sizeof() is compile-time only, its not a function, its a compiler macro to return the number of bytes of storage a variable of that type uses.