How does a comma separation function when declaring variables

Question

I had made an error in my code at one point when I forgot to end a variable initialization with a semicolon and instead had put a comma. However, to my surprise it never returned an error and the code worked like normal.

Therefore I was wondering how this works ? I simplified my code by writing the below code;

uint32_t randomfunction_wret()
{
  printf("(%d:%s) - \n", __LINE__, __FILE__);
  return 6;
}

uint32_t randomfunction()
{
  printf("(%d:%s) - \n", __LINE__, __FILE__);
}

int main()
{
    uint32_t val32 = 3, randomfunction_wret(), valx = 6, randomfunction();

    printf("(%d:%s) - %u %u\n", __LINE__, __FILE__, val32, valx);

   return 0;
}

When executed is returns;

(43:test.c) - 3 6

I am very shocked that there is no error when I have functions separated in my initialization. However the functions were not even being called.

============== UPDATED

How about if the code was as follows, from what I see, now each function is called;

int main()
{
    uint32_t val32;

    val32 = 3, randomfunction_wret(), randomfunction();

    printf("(%d:%s) - %u \n", __LINE__, __FILE__, val32);

   return 0;
}

Output would be

(23:test.c) - 
(29:test.c) - 
(38:test.c) - 3 

Answer 1

The line

uint32_t val32 = 3, randomfunction_wret(), valx = 6, randomfunction();

is equivalent to;

uint32_t val32 = 3;                // Defines and initializes the variable.
uint32_t randomfunction_wret();    // Re-declares the function. Nothing else is done.
uint32_t valx = 6;                 // Defines and initializes the variable.
uint32_t randomfunction();         // Re-declares the function. Nothing else is done.

The variables used in the function are properly defined and initialized. Hence, the function works without any problem.

---

Just as an aside, the implementation of randomfunction() does not have a return statement. Using it will cause undefined behavior.

---

Update, in response to the edited post.

Due to operator precedence, the line

val32 = 3, randomfunction_wret(), randomfunction();

is equivalent to:

(val32 = 3), randomfunction_wret(), randomfunction();

All the sub-expressions of the comma separated expression are evaluated. Hence, the functions randomfunction_wret and randomfunction are called and their return values are discarded.