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What does … mean in an argument list in C ?

I was reading a book about win32 programming and i saw a function like this:

   int CDECL MessageBoxprintf(TCHAR *szCaption,TCHAR *szFrmat,...)  
   {
       TCHAR szBuffer[1024];
       va_list pArgList;
       va_start (pArgList,szFrmat);
      _vsnprintf(szBuffer,sizeof(szBuffer)/sizeof(TCHAR),szFrmat,pArgList);
       va_end (pArgList);
       return MessageBox(NULL,szBuffer,szCaption,0);
    }

what does ,... means in the parameters of a function?

I tried to find answers with searching but i got nothing useful.

Answer 1

It means you can have varible numbers of arguments to that function instead of a fixed number of arguments.
A perfect usecase would be

For example Lets say we have a function called average

double average ( int num, ... )
{
  va_list arguments;                     // A place to store the list of arguments
  double sum = 0;

  va_start ( arguments, num );           // Initializing arguments to store all values after num
  for ( int x = 0; x < num; x++ )        // Loop until all numbers are added
    sum += va_arg ( arguments, double ); // Adds the next value in argument list to sum.
  va_end ( arguments );                  // Cleans up the list

  return sum / num;                      // Returns the average
}

you can call this function like this with any number of arguments

cout<< average ( 3, 12.2, 22.3, 4.5 ) <<endl; 

Also the arguments passed don’t have to be of the same type.
For more information look at this link