Thread: Setting a value with a generic pointer.

I have a generic pointer cause I need to work with different data types (uint8_t, int, float)

Code:

 void *iter_first;

now I initialize it

Code:

uint8_t flag[8];
iter_first = &flag[4];

till now it's OK. but now I want to set a value and I should decide the size of the value.

Code:

int size = sizeof(iter_first);

if (size == 1)
    (*((uint8_t *)iter_first)) = iter_first_val;
else
    (*((int *)iter_first)) = iter_first_val;

size always 4 so I override all the bunch flag[4] - flag[7].

and if I try to cast

Code:

(uint8_t *)iter_first = &flag[4];

I get - Error[Pe137]: expression must be a modifiable lvalue

What do I miss?

Something like

Code:

struct foo 
  enum { IS_CHAR, IS_INT, IS_DOUBLE } type;
  union {
    char *cp;
    int *ip;
    double *dp;
  } v;
};

int main  ( ) {
  struct foo bar;
  int val;
  bar.type = IS_INT;
  bar.v.ip = &val;

  /// 

  switch ( bar.type ) {
    case IS_INT:
  }

Originally Posted by Salem

Something like

yes but on 100 v I need 100 type - added RAM waste (in my case it's embedded, RAM limited system). I thought there is a way to avoid it.
why the compiler rejects the cast

Code:

(uint8_t *)iter_first = &flag[4];

what's criminal in it?

ОК. what about

Code:

if (val < 256)
    (*((uint8_t *)generic)) = val;
else
   (*((int *)generic)) = val;

any way it would be properly aligned in memory? wouldn't it?

> yes but on 100 v I need 100 type - added RAM waste
It's a union.
No matter how many pointer types you store in your union, it will only be as big as a pointer.