Function call with arguments

Projects Programming
1

Can't pass arguments to function.

    void renderFF(void (*draw_fn)((*t1), (*t2), (*t3)) )
    {
      uint32_t time;
      time = millis() + 10;

      do {
        u8g2.clearBuffer();
        draw_fn(t1, t2, t3);
        u8g2.sendBuffer();
      } while ( millis() < time );
    }

gfx.renderFF(message.info("Hello!", "I am console,", "how are you?"));
2

What are the types of t1,t2 and T3?

3

type String

4

How would the compiler know that?

5 
    void renderFF( void (*draw_fn)(String *a, String *b, String *c) )
    {
      uint32_t time;
      time = millis() + 10;

      do {
        u8g2.clearBuffer();
        draw_fn(a, b, c);
        u8g2.sendBuffer();
      } while ( millis() < time );
    }
1 Like
6

To pass both a function pointer and its arguments, you can use something like this:

void renderFF(
    void (*draw_fn)(String, String, String),
    String a, String b, String c) {
  // ...
  draw_fn(a, b, c);
  // ...
}

Then you need a function that is of the right type, e.g.,

void f(String a, String b, String c) {
  // Do something with a, b and c.
}

And you can call this as follows.

renderFF(f, "brave", "new", "world");

Note that this will not work for class methods (like message.info), that requires a more complicated setup.

1 Like
7

that's the syntax to call a function.
Parameters should stand separated as proposed by @jfjlaros
with a bit of work you could use the ellipsis ... to use variable number of parameters.

something like this:

void printText(const char * text) {
  Serial.println(text);
}

void renderFF(void (*draw_fn)(const char *), int count, ...)
{
  va_list list;	                      // va_list from <cstdarg>. list is its type, used to iterate on ellipsis
  va_start(list, count);              // Initialize position of va_list
  for (int i = 0; i < count; i++) { 	// Iterate through every argument
    draw_fn(va_arg(list, const char *));
  }
  va_end(list);	// Ends the use of va_list
}

void setup() {
  Serial.begin(115200);
  renderFF(printText, 3, "Hello!", "I am console,", "how are you?");
}

void loop() {}
1 Like
8

Thank you so much! I completely forgot that you can do this. I thought and puzzled over the pointers. The solution is simple. Thanks again!

9

Thank you so much! An interesting decision.

10

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