Unlimited Arguments (...)
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Ok, I''ve never gotten around to learning it, simply because I''ve had no need to. But now, I''ve found a very good place in which I could use the unlimited arguments thingy, or whatever it''s called. I know the function would be declared as so:
int Unlimited(int hi, ...)
and now the programmer can enter in lots of ints. However, how do I find out how many params were sent through and how do I use each of them. Any help would be appreciated, as usual
usually, its used for string formatting
this is how you do it to have a formatted string like the printf()
its pretty simple actually
if you want it for something other than printing a formatted string into a buffer, then i cant help you, this is all i know about variable arguments
anyway, hope this helps
this is how you do it to have a formatted string like the printf()
#include <stdio.h> //needed for variable arguments//void *Something(const char *String, ...){ char Buffer[256]; //this holds the final string va_list ArgList; //this is the argument list va_start(ArgList, String); //begins processing the arguments vsprintf(Buffer, String, ArgList); //print the string into Buffer va_end(ArgList); //finished processing the arguments} its pretty simple actually
if you want it for something other than printing a formatted string into a buffer, then i cant help you, this is all i know about variable arguments
anyway, hope this helps
Here is the code for a simple routine I use to output debug information. You can use it like so:
FileDebug("Line %d, Error\n",iLine);
Here is the code:
void FileDebug( char *msg, ... )
{
FILE *fp;
va_list arglist;
char msgbuf[32768];
va_start( arglist, msg );
vsprintf( &msgbuf[0], msg, arglist );
va_end( arglist );
fp = fopen("debug.txt","a+");
fprintf( fp, msgbuf );
fclose( fp );
}
Look into the va_start family of functions. They are called variable-argument lists.
Hope that helps!
FileDebug("Line %d, Error\n",iLine);
Here is the code:
void FileDebug( char *msg, ... )
{
FILE *fp;
va_list arglist;
char msgbuf[32768];
va_start( arglist, msg );
vsprintf( &msgbuf[0], msg, arglist );
va_end( arglist );
fp = fopen("debug.txt","a+");
fprintf( fp, msgbuf );
fclose( fp );
}
Look into the va_start family of functions. They are called variable-argument lists.
Hope that helps!
Here is an example from the VC docs that I found to be helpful when researching this:
Note that in this example they are assuming that the function will be terminated with a -1. So you would call it like:
average(1,2,3,-1)
All stdarg systems have to have some kind of terminator, because the va_arg function is just getting an address and incrementing it; it can''t infer how long your list is unless you tell it. Functions like printf() figure out the length of the list by parsing the initial string argument (ie- counting the number of
%d, etc markers).
HTH
/* Returns the average of a variable list of integers. */int average( int first, ... ){ int count = 0, sum = 0, i = first; va_list marker; va_start( marker, first ); /* Initialize variable arguments. [ie- tell the program the starting address] */ while( i != -1 ) { sum += i; count++; i = va_arg( marker, int); } va_end( marker ); /* Reset variable arguments. */ return( sum ? (sum / count) : 0 );} Note that in this example they are assuming that the function will be terminated with a -1. So you would call it like:
average(1,2,3,-1)
All stdarg systems have to have some kind of terminator, because the va_arg function is just getting an address and incrementing it; it can''t infer how long your list is unless you tell it. Functions like printf() figure out the length of the list by parsing the initial string argument (ie- counting the number of
%d, etc markers).
HTH
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