Is it possible to create a function with a variable number of passed arguments using this compiler?
I have seen discussions where some C++ compilers handle a variable number of arguments e.g. http://www.codersource.net/c++_variable_argument_functions.html
Thanks.
I am experimenting with this code, but the results are not what they should be:
Arg a: 2
Arg b: 4
Arg c: 3840
Arg d: 3841
7687
#include <stdio.h>
//#include <stdargs.h>
int Add(int a,int b,...)
{
//This one handles 4 arguments in total.
int l_ParamVal=0;
int total=0;
int i;
//Declare a va_list macro and initialize it with va_start
va_list l_Arg;
va_start(l_Arg,a);
//The required parameters can also be accessed directly
l_ParamVal = a;
Serial.print("Arg a: ");
Serial.println(l_ParamVal);
if(l_ParamVal != -1)
total = total +l_ParamVal;
l_ParamVal = va_arg(l_Arg,int);
Serial.print("Arg b: ");
Serial.println(l_ParamVal);
if(l_ParamVal != -1)
total = total +l_ParamVal;
l_ParamVal = va_arg(l_Arg,int);
Serial.print("Arg c: ");
Serial.println(l_ParamVal);
if(l_ParamVal != -1)
total = total +l_ParamVal;
l_ParamVal = va_arg(l_Arg,int);
Serial.print("Arg d: ");
Serial.println(l_ParamVal);
if(l_ParamVal != -1)
total = total +l_ParamVal;
va_end(l_Arg);
return total;
}
void setup ()
{
Serial.begin(9600);
Serial.println(Add(2,3,4));
}
void loop() {
delay(1000);
}
"b" is not part of your variable arguments list, so doesn't need
_ParamVal = va_arg(l_Arg,int);
Serial.print("Arg b: ");
Serial.println(l_ParamVal);
if(l_ParamVal != -1)
total = total +l_ParamVal;
If you declare "int Add (int a,...)"
your sketch will work as is (except for arg d).
I guess that really wasn’t a very good example since it didn’t really handle a variable number of arguments.
This code is better but the check for the last argument (where the value is -1) doesn’t work.
I’ve been trying to adapt code from:
http://msdn.microsoft.com/en-us/library/kb57fad8(VS.80).aspx and from the Sprite.cpp library.
It works for a while, returns 0 instead -1 from the va_arg macro, returns other garbage values and keeps looping …
Results:
a: 2
total: 2
a: 3
total: 5
a: 4
total: 9
a: 0
total: 9
a: 0
total: 9
a: 0
total: 9
a: 97
total: 106
a: 32
total: 138
a: 116
total: 254
…etc
#include <stdio.h>
//#include <stdargs.h>
int Add(uint8_t a, ...)
{
//This one handles 4 arguments in total.
int total=0;
//Declare a va_list macro and initialize it with va_start
va_list l_Arg;
va_start(l_Arg, a);
while( a != -1 ) {
Serial.print("a: ");
Serial.println(a, DEC);
total += a;
Serial.print("total: ");
Serial.println(total);
a = va_arg(l_Arg, int); // using '...' promotes uint8_t to int
}
va_end(l_Arg);
return total;
}
void setup ()
{
Serial.begin(9600);
Serial.println(Add(2,3,4));
}
void loop() {
delay(1000);
}
Returning "-1" when using a signed data type doesn't seem to me to be a sensible strategy. ;)
I found another example of code that seems more logical - the first argument indicates the number of subsequent arguments. It produces the desired result.
valu: 2 total: 2
valu: 3 total: 5
valu: 4 total: 9
9
#include <stdio.h>
int Add(int num, ...) {
int valu;
int total=0;
//Declare a va_list macro and initialize it with va_start
va_list argList;
va_start(argList, num);
for(; num; num--) {
valu = va_arg(argList, int);
Serial.print("valu: ");
Serial.print(valu, DEC);
total += valu;
Serial.print(" total: ");
Serial.println(total);
}
va_end(argList);
return total;
}
void setup ()
{
Serial.begin(9600);
Serial.println(Add(3,2,3,4)); //first arg is number of subsequent variables
}
void loop() {
delay(1000);
}