Is there a C compiler flag to check function modified input parameter?

Question

I was wondering, is there a flag for the C compiler ( i.e. GCC or GHS) to check whether an input parameters is modified or not?

I mean, if I have the following function, x and y may be modified within the function ( as it happening now) if I don't add the const to them. So I was wondering whether the compiler can detect that situation or not and whether there exists a flag to do so.

int16_t myFunc(int16_t* x ,int16_t* y, bool* e) 
{   
     int16_t z = 0;

     z = *x + *y;
     *x = 16; // this is wrong on purpose and I would like to detect it
      
     if ( z < 0)
     {
         *e = true;
     }

    return z;
}

Answer 1

The only thing you want to do here is use const like this:

int16_t myFunc(const int16_t* x ,int16_t* y, bool* e)
{
   ...
   *x = 42;  // compiler error here
   ...
}

Here the compiler will issue a diagnostic such as assignment of read-only location '*x'.

That's what the const keyword is used for, that's the "flag" you're looking for.

You should put const on pointer parameters whenever possible. If you know that the object pointed by a parameter won't be modified, use const.