int f(int z) {
    return z + (z*2) + z/3 + z*z + 23;
}


int main()
{
  int i = 7;
  f(i); ///// <<----- here I disregard the return value

  return 1;
}

#define WARN_UNUSED __attribute__((warn_unused_result))

int WARN_UNUSED f(int z) {
    return z + (z*2) + z/3 + z*z + 23;
}

int main()
{
  int i = 7;
  f(i); ///// <<----- here i disregard the return value
  return 1;
}

$ gcc test.c
test.c: In function `main':
test.c:16: warning: ignoring return value of `f', declared with
attribute warn_unused_result

unsigned long __must_check copy_to_user(void __user *to,
                                        const void *from, unsigned long n);

int fn() __attribute__((warn_unused_result));

class return_value
{
public:
  explicit return_value(T value)
    :value(value), checked(false)
  {
  }

  return_value(const return_value& other)
    :value(other.value), checked(other.checked)
  {
    other.checked = true;
  }

  return_value& operator=(const return_value& other)
  {
    if( this != &other )
    {
      assert(checked);
      value = other.value;
      checked = other.checked;
      other.checked = true;
    }
  }

  ~return_value(const return_value& other)
  {
    assert(checked);
  }

  T get_value()const {
    checked = true;
    return value;
  }

private:
  mutable bool checked;
  T value;
};

grep -rn "function_name" * | grep -v "="

if (signal(SIGHUP, SIG_IGN) != SIG_IGN)
    signal(SIGHUP, sighandler);

if ((old = signal(SIGHUP, SIG_IGN)) != SIG_IGN)
    old = signal(SIGHUP, sighandler);