Ellipsis Operator

[Nick101]

Hello,
Can someone explain how to use Ellipsis ( ... ) operator? I found a very short explanation in the help file which is I can not understand how to use it to create a variable number argument function. Here is what I found in the help file :

Ellipsis ('...') Operator
An ellipsis ('...') consists of three successive periods with no whitespace intervening. You can use an ellipsis in the formal argument lists of function prototypes to indicate a variable number of arguments, or arguments with varying types. For example:



void func (int n, char ch, ...);
This declaration indicates that func will be defined in such a way that calls must have at least two arguments, an int and a char, but can also have any number of additional arguments.

Example:

#include <stdarg.h>


int addvararg(char a1,...){
va_list ap;
char temp;
va_start(ap,a1);

while( temp = va_arg(ap,char))
a1 += temp;
return a1;
}


int res;
void main() {


res = addvararg(1,2,3,4,5,0);

res = addvararg(1,2,3,4,5,6,7,8,9,10,0);

}//~!

[design4]

Hello,
Can someone explain how to use Ellipsis ( ... ) operator? I found a very short explanation in the help file which is I can not understand how to use it to create a variable number argument function. Here is what I found in the help file :

Ellipsis ('...') Operator
An ellipsis ('...') consists of three successive periods with no whitespace intervening. You can use an ellipsis in the formal argument lists of function prototypes to indicate a variable number of arguments, or arguments with varying types. For example:



void func (int n, char ch, ...);
This declaration indicates that func will be defined in such a way that calls must have at least two arguments, an int and a char, but can also have any number of additional arguments.

Example:

#include <stdarg.h>


int addvararg(char a1,...){
va_list ap;
char temp;
va_start(ap,a1);

while( temp = va_arg(ap,char))
a1 += temp;
return a1;
}


int res;
void main() {


res = addvararg(1,2,3,4,5,0);

res = addvararg(1,2,3,4,5,6,7,8,9,10,0);

}//~!

Hello

Im also looking for the example because there is no vsnprintf in the stdarg. I want to build a string with some other int variable inside it

Regret

[filip]

Hi,

Maybe the following example will help :

Code: Select all

// using ellipsis to get the average value of the variable number of parameters

#include <stdarg.h>

// average result value is placed here
double result;

// The ellipsis must be the last parameter
// count is how many additional arguments we're passing
double findAverage(int count, ...) {
    // sum value is placed here
    double sum = 0;
    
    // counter variable
    int i = 0;

    // We access the ellipsis through a va_list, so let's declare one
    va_list list;

    // We initialize the va_list using va_start.  
    // The first parameter is the list to initialize.  
    // The second parameter is the last non-ellipsis parameter.
    va_start(list, count);

    // Loop through all the ellipsis arguments
    for (i=0; i < count; ++i)
         // We use va_arg to get parameters out of our ellipsis
         // The first parameter is the va_list we're using
         // The second parameter is the type of the parameter
         sum += va_arg(list, int);

    return sum / count;
}

void main() {
  result = findAverage(5, 1, 2, 3, 4, 5);
  result = findAverage(6, 1, 2, 3, 4, 5, 6);
}

Basically, we are doing the following here :

• Define a function with its last parameter as ellipses (i.e. ...) and the one just before will represent the number of arguments.
• Create a va_list type variable in the function definition (this type is defined in stdarg.h header file).
• Use the first parameter and va_start macro to initialize the va_list variable to an argument list (the macro va_start is defined in stdarg.h header file).
• Use va_arg macro and va_list variable to access each item in argument list.

Regards,
Filip.

[design4]

Hi,

Maybe the following example will help :

Code: Select all

// using ellipsis to get the average value of the variable number of parameters

#include <stdarg.h>

// average result value is placed here
double result;

// The ellipsis must be the last parameter
// count is how many additional arguments we're passing
double findAverage(int count, ...) {
    // sum value is placed here
    double sum = 0;
    
    // counter variable
    int i = 0;

    // We access the ellipsis through a va_list, so let's declare one
    va_list list;

    // We initialize the va_list using va_start.  
    // The first parameter is the list to initialize.  
    // The second parameter is the last non-ellipsis parameter.
    va_start(list, count);

    // Loop through all the ellipsis arguments
    for (i=0; i < count; ++i)
         // We use va_arg to get parameters out of our ellipsis
         // The first parameter is the va_list we're using
         // The second parameter is the type of the parameter
         sum += va_arg(list, int);

    return sum / count;
}

void main() {
  result = findAverage(5, 1, 2, 3, 4, 5);
  result = findAverage(6, 1, 2, 3, 4, 5, 6);
}

Basically, we are doing the following here :

• Define a function with its last parameter as ellipses (i.e. ...) and the one just before will represent the number of arguments.
• Create a va_list type variable in the function definition (this type is defined in stdarg.h header file).
• Use the first parameter and va_start macro to initialize the va_list variable to an argument list (the macro va_start is defined in stdarg.h header file).
• Use va_arg macro and va_list variable to access each item in argument list.

Regards,
Filip.

Thank you. But can u tell me how to solve below problem?

Code: Select all

main()
{
  char IDE[7] = "MikroC";
  int version = 6;
  
  MyUART1Print("Hello, Im using %s version %d", IDE, version);
}

//Then here is the function code with 1 buffer to be transmit using "UART1_Write_Text(buffer)";

Can u help me use (...) ? Because I want to combine other variable in one buffer. I cannot simply write "UART1_Write_Text("Hello, Im using %s version %d", IDE, version)".

Thanks in advanced