What are variadic functions (va_list) in C?

Source code can be found here:
code-vault.net/lesson/cc1b934...
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[@kookts8491]

The last one in the playlist🎉🥳 Thank you so much!!!

[@peyop5262]

I've used it to write a generic "err_exit" function, which basically takes a return error int as first parameter, then as much strings as needed. For example 'err_exit(1, "", SDL_GetError(), NULL);'
It makes my code cleaner (exit program in a single line and customized error message) and it's really helpful when a project gets big.
As you've mentioned, here the NULL last arg isn't a problem since variadic args are strings. Very handy C functionality if you treat it carefully.
Thank you for your amazing videos

[@anilthapa6290]

Hi very good explanation of the topic. Learned so much from your channel.

[@mustaphaboudrik5390]

Thanks a lot for the Explanation

[@AlluAdarsh]

Informative. Thank you!

[@riemann4151]

best channel on C.

[@yrds96]

Great video
I didn't knew about the NULL technique

[@user-mo6vz5mg3t]

lol the adds started exactly at the moment when he tried to compile with 10 iterations instead of 4 at 9:24
This was an undefined behaviour indeed

[@akpevwepraise4208]

the most perfect explanation sofar

[@189Blake]

The C23 new syntax seems very useful, could you do a blog post or a follow up explaining that? Just a video idea

[@CodeVault]

Thanks for the suggestion. I will look into it

[@julietagoldbaum332]

Excelent video!!. congrats from Argentina!!. What is it argument promotion in variadic functions?

[@CodeVault]

That is quite a complex topic which I will cover in a video. The basic idea is that parameters for variadic functions are treated as certain data types by default

[@dimitrioskalfakis]

tricky. good effort.

[@bjornnordquist1616]

Hi! Interesting video. You have been asking for content ideas in the past, so maybe there is something for you in here: there appears to be almost no content about testing in C. Or maybe it is just really hard to dig up for me. I barely know where to start, especially since all content send to focus on C++ and Visual Studio appears to have a dislike for C in general. Also, maybe how far can we emulate object oriented programming or functional programming in C? And in the same direction procedural programing with C. Either way I'll keep watching these C videos until I move on. Thanks a lot!

[@CodeVault]

Thanks for the suggestions. I have dabbled in automated testing but not in C specifically (I'll have to do some research). And regarding emulating OOP in C... it was always in my mind since it's a great way of learning the basics of OOP and how it's a paradigm that can be used in almost any language

[@nayyerabbas7174]

Very informative. Can you make a video on opaque pointer in c.

[@CodeVault]

I will look into it

[@Notthetylor]

I'd like to have a mentor like u!!

[@fifaham]

Having 0 in the list while using the NULL method could be troublesome for embedded design - the hardware may not behave well or the robot arm may grab the wrong object.

[@vilijanac]

Is it possible to pass an int array instead sum({1,2,3}), where you have int sum(int args[]){...int count = sizeof(args);...}
I forgot about this.

[@CodeVault]

In other languages it might be possible. In C you have to first declare and initialize an array before you pass it to the function

[@vilijanac]

@@CodeVault ok, thx, reason also for va_list implementation and passing count. It is better then testing for NULL.

[@XAENDER196]

Hi! Is it possible to pass char array to parameters? i mean, can they be as variadic arguments?

[@CodeVault]

You can pass any type of variables you want to va_list

[@ryanboudwin541]

Why not pass argc from your main into the function instead of a separate int count?

[@CodeVault]

The argc value is the number of parameters passed to the executable

[@shenghongzhong]

Did we know which video he referred to was about not using the null terminator and the number of elements?

[@CodeVault]

There's no video about that. I recommended this as a homework, but I can help with that if you need it

[@zyghom]

nice, so how come printf does not need count? ok, that is the homework ;-)

[@CodeVault]

Exactly. Hint: It might have to do with those pesky %d and %s you need to specify to printf

[@belayoub6055]

@@CodeVault well you need to count how many % that specify the format no ?

[@CodeVault]

@@belayoub6055 Exactly

[@rotemlv]

I wouldn't recommend using the last trick you showed, as the code will return bad results on some inputs (0s spell trouble when comparing to NULL).
Try this main on your code:
int main() {
printf("A list of stuff: %d
", sum(1,2,3,4,5,6,0,999, NULL));
return 0;
}
You will get the expected (by me) 21, and ignore the 999.
Yeah, one might say this is an edge case, but I wouldn't.

[@CodeVault]

I fully agree. That's what I warned people about in the video. It works well if you pass strings (or other pointer types) for example