How can we make this code work for Arduino?
double sum (int num, ... )
{
va_list arguments;
double sum = 0;
va_start (arguments, num);
for (int x = 0; x < num; x++)
{
sum += va_arg (arguments, double);
}
va_end (arguments);
return sum;
}
String append (int num, ... )
{
va_list arguments;
String str = "";
va_start (arguments, num);
for (int x = 0; x < num; x++)
{
str += va_arg (arguments,String);
}
va_end (arguments);
return str;
}
function arrOfFunctions[] = { sum, append };
void setup () {
double testSum = arrOfFunctions[0](1,2,3);
String testSum = arrOfFunctions[1]("a","b","c","d");
}
void loop () { }
westfw
February 19, 2020, 10:18pm
2
Where are you getting the definition of "function" ?
In what way does it not work?
double testSum = arrOfFunctions[0](1,2,3);
Doesn't that need to be more complicated, something like:
double testSum = (*arrOfFunctions[0])(1,2,3);
(Hmm. Perhaps not...)
What makes you think it doesn't work? variadic function support has been a part of the c language since its inception in the '70s, and is absolutely supported on Arduino. I use it all the time....
Regards,
For the sum function you need to pass the number of values as an int and then that many double values. For example:
sum(3, 1.0, 2.0, 3.0);
For the append function, the same applies except the variadic arguments need to be String objects:
append(4, String("a"), String("b"), String("c"), String("d"));
(Untested.)
Also, it might be better to make it take plain c-strings (const char *) so you don't have to pass a copy of each String object to the function.
You cannot put append() and sum() into an array because they are not the same type.
To use C-style variadic function, you must:
#include <stdarg.h>
Your code with minor modification: #include <stdarg.h>double sum (int num, ... ) { } String append (int num, ... ) { } void setup () { } void loop () { }
Note: Code compiled but not tested.
gfvalvo
February 19, 2020, 11:56pm
7
jimLee:
Sounds complicated.
-jim lee
If you've ever used any of the printf() family of functions, then you've used a Variadic.
gcjr
February 19, 2020, 11:57pm
8
with modifications to append() to used char[] instead of String, the following works for me
printf ("%s: %f\n", __func__, sum (3, 2.2, 3.3, 100.1));
printf ("%s: %s\n", __func__, append (3, "how", " now", " brown"));
as arduino_new already said, beside a compiler error, the following doesn't make sense because the functions have different return types.
function arrOfFunctions[] = { sum, append };
the following compiled, but i was not able to use the function pointers instead of sum() or append() above
double (*pSum) (int, ...) = sum;
char* (*pAppend) (int, ...) = append;
westfw
February 20, 2020, 12:00am
9
You cannot put append() and sum() into an array because they are not the same type.
Would C++ overloading let you do it you specified the first differing argument? (Hmm. Can overloaded functions have different return types?)
String append (int num, String *,... );
double sum (int num, double ... );
westfw:
String append (int num, String *,... );
double sum (int num, double ... );
No function cannot be overload with only different in return type.
double sum(double value)
{
return value;
}
template<typename... Args> double sum(double value, Args... UserArgs)
{
return value + sum(UserArgs...);
}
String append(String value)
{
return value;
}
template<typename... Args> String append(String value, Args... UserArgs)
{
return value + append(UserArgs...);
}
void setup () {
Serial.begin(9600);
double total = sum(1.0d, 2.0d, 3.0d);
String result = append("a", "b", "c", "d");
Serial.println(total);
Serial.println(result);
}
void loop () { }