Thread: Variable-length arg lists?

I have just started with Functions with variable-length argument lists, and I thought i would try using it to "optimise" one of the functions I already have. I have tryed implementing it, the compiler produces not errors/warnings, so when run the program crashes. Here is what I have currently:

Code:

void InsertRow(HWND hwnd, char *col1, char *col, ...)
{
	LV_ITEM lvItem;
	va_list arguments;
	int i;

	lvItem.mask = 0;
	lvItem.iItem = 0;
	lvItem.iSubItem = 0;
	lvItem.iItem = ListView_InsertItem (hwnd, &lvItem);

	lvItem.mask = LVIF_TEXT;
	lvItem.pszText = col1;
	lvItem.cchTextMax = strlen (lvItem.pszText);
	ListView_SetItem(hwnd, &lvItem);

        va_start (arguments, col);
	for (i=0; col!=0; i++) {
		lvItem.iSubItem = (i+1);
		lvItem.pszText = va_arg ( arguments, char *);
		ListView_SetItem(hwnd, &lvItem);
	}
	va_end (arguments);
}

I know the for loop needs fixing (its probably col!=0 [i've tried !=NULL same thing happens]) but I don't know how to fix this. Any ideas? I think (hope) this is code stright forward, if not say and I will post the old code (longer, but works).

printf( "%d %d", num1, num2 );
This is an example of a vararg function which encodes the number of variable parameters in the control string. Count the number of % to determine the expected number of parameters.

execl("prog","prog","arg","arg",(char*)NULL);
This is an example of a vararg function which has a specific value (a NULL pointer) to mark the end of the list.

You need to include a mechanism by which the number of arguments can be determined. There is no automatic means to do this.

Or pass an argument that contains the number of variable arguments you passed.

Thanks, I think I will go with Elysia's suggestion to pass in the number of arguments. With the function I have now, col1 is inserted fine, but the second col has been replaced with the third col. To put this another way, the forth parameter gets replaced with the fith, and so on. Here is the code:

Code:

void InsertRow(HWND hwnd, int argcount, char *col1, char *col, ...)
{
	LV_ITEM lvItem;
	va_list arguments;
	int i=0;

	//Omitted region Same as above, works fine

        va_start (arguments, col);
	for (i=0; i<=argcount; i++) {
		lvItem.iSubItem = (i+1);
		lvItem.pszText = va_arg ( arguments, char *);
		ListView_SetItem(hwnd, &lvItem);
	}
	va_end (arguments);
}
//Called with the following:
InsertRow(GetDlgItem(hwndMain, ID_LISTVIEW), 7, szProcessName,
 PIDbuf,GetProcessMemoryWSS(hProcess, buf), GetProcessMemoryPWSS(hProcess, buf),
 GetProcessPriority(hProcess), GetUserInfo(dwProcesses[i], hProcess));

Code:

	for (i=0; i<=argcount; i++) {

I notice one subtle bug here. Count starts from 1 and index starts from 0. So it should be i < argcount, otherwise you're going to read 6 arguments instead of 5 when you pass 5.

Thanks for the quick reply, but this doesn't fix the problem. whatever I change lvItem.iSubItem to it doesn't work. Changing it to i+2, leaves the second column blank, for some reason. I think va_arg ( arguments, char *); is getting the second argument instead of the first.

---FIXED---
I have currently fixed the problem with an if statement, meh it works. Since what should have worked perfectly well, logically, didn't I tried the following (for loop only the ret is above):

Code:

for (i=0; i<argcount; i++) {
	lvItem.iSubItem = (i+1);
	if (i==0) lvItem.pszText = col;
	else lvItem.pszText = va_arg ( arguments, char *);
	ListView_SetItem(hwnd, &lvItem);