Sizeof with char*

Projects Programming
1

I'm using sizeof and strlen. With the char* strings I get back the right number from strlen, but it always kicks back "2" from sizeof.
Doing the same with a string - that doesn't use char* - I get the right numbers back (from sizeof and strlen).

char *testStrings[5] = {"abcd", "abcde", "abcdef", "abcdefg", "abcdefgh"};
int numero;

const char fixedstr[] = "tenletters";

void setup() 
{
  Serial.begin(19200);
  Serial.print("ok\r\n\");
}

void loop() 
{
  Serial.print("strlen tS_[0] = ");
  numero = strlen(testStrings[0]);
  Serial.println(numero);
  Serial.print("sizeof tS[0] = ");
  numero = sizeof(testStrings[0]);
  Serial.println(numero);  

  Serial.print("strlen tS[4] = ");
  numero = strlen(testStrings[4]);
  Serial.println(numero);
  Serial.print("sizeof tS[4] = ");
  numero = sizeof(testStrings[4]);
  Serial.println(numero);

  Serial.print("strlen FC = ");
  numero = strlen(fixedstr);
  Serial.println(numero);
  Serial.print("sizeof FC = ");
  numero = sizeof(fixedstr);
  Serial.println(numero);
  
  delay(2000);

  Serial.print("\r\n\r\n");
}
2

The size of a pointer is 2 (bytes) and an 8-bit AVR processor.

3

You're saying that it's kicking back the size of the pointer (not the number of characters in the string)?

4

Correct. You asked for sizeof() a pointer variable and that's what it gave you.

5

If you want the number of characters in a C string, use 'strlen(char *pointer)'. It counts bytes until it reaches a zero byte.

If the pointer points to an array that is NOT a C string (does NOT have a null character terminator) then you have to pass the size separately. Pointers are just an address.

6

sizeof() is evaluated at compile time, not runtime.

7

This topic was automatically closed 120 days after the last reply. New replies are no longer allowed.