Using qsort() To Sort An Array | C Programming Example

[@AfifaSadiq]

The compare function is so well explained.

[@pratham8275]

Thanks for explaining qsort

[@idkzsh]

you explained this so much better than my prof. prof puts me to sleep.

[@PortfolioCourses]

Hahaha I'm sorry your prof puts you to sleep! I'm glad this video was able to help you out! :-)

[@madmademoiselle097]

thank you, a clear, easy to understand tutorial!

[@PortfolioCourses]

You're very welcome, I'm glad you found it easy to understand! :-)

[@gammyhorse]

So basically, if I understood correctly, the 4th argument of qsort is a function pointer returning an int, which is very interesting if this is the case. Function pointers are powerful and I would like to know more about their use in practice. Thank you.

[@PortfolioCourses]

Yes, exactly, it's a pointer to a function which returns an int. :-) You may have already seen this video on function pointers but I thought I'd share it just in case: kzbin.info/www/bejne/nJDYiIKNi86MmZI

[@gammyhorse]

@@PortfolioCourses Thank you very much!

[@PortfolioCourses]

You’re welcome! :-)

[@PortfolioCourses]

@@johngormley1394 That's very cool John, thanks for sharing, definitely a good application of function pointers. 🙂

[@decumon]

thanks from russia, first video about comparator that i found

[@PortfolioCourses]

You're welcome! :-)

[@ongayijohnian8787]

I still dont get how qsort works with the x and y, does it iterate in the loop assigning a digit x and its successor y?

[@akshatkhatri1167]

great video so if we want to use it with array of structures instead of integer array; how exaclty will the casting be done i m a bit confused

[@PortfolioCourses]

It’s done pretty much the same way, maybe the example in this link can help you out? :-) iq.opengenus.org/qsort-in-c/amp/

[@ismbks]

does the compare function has to take const void pointer as parameters? or could it also take another type like const int pointer, so we don't need to use pointer magic and keep the code a bit more simple?

[@philipphortnagl2486]

I don't get how the compare function works without giving any arguments. I mean you say, we assume the numbers "2" and "5" from the array, but how is this actually working in the function without explicitly giving any arguments for the function?

[@PortfolioCourses]

Great question Philipp! :-) So when we pass compare to qsort() like this: qsort(a, length, sizeof(int), compare); We aren't actually *calling* compare() in that moment. We're actually passing the function itself as an argument to qsort(). And then at a later point the qsort() function will be what actually calls compare()! It will call it and provide it with the arguments to compare, and it will use the return value of the compare() function to help sort the array. We call this a "callback function": en.wikipedia.org/wiki/Callback_(computer_programming). It is a bit unusual because normally we pass values to functions, like 2.5, etc. Technically what is being passed is the memory address of the compare function, and qsort() is able to use that to call the function. In C we call that a function pointer, there is a video on the concept here: kzbin.info/www/bejne/nJDYiIKNi86MmZI.

[@pousemad]

amazing video, thank you so much!!

[@PortfolioCourses]

You're welcome, I'm very glad you enjoyed it! :-)

[@kianoushmehrandish7818]

have you created a same video for sorting structs?

[@PortfolioCourses]

No, but that's a great idea Kianoush, maybe I can do a video on that one day though. :-) It would be very, very similar to what we've done in this video though. The difference would be here: int x = *(int *)x_void; ...instead of a type cast using int, it would be a typecast using the struc type. So instead of 'int' it should be something like 'struct name_of_struct'.

[@ishanrana8402]

Thank you this was very helpful

[@PortfolioCourses]

You’re welcome Ishan! :-)

[@rishabhpandey12aroll7.5]

Thanks, this really helped

[@demiancoorey2394]

First class tutorial

[@PortfolioCourses]

I’m glad you enjoyed it Demian! :-)

[@nguyentuan-ef5hr]

Hmm why when you read the array and call qsort you can know is 2-7 but not 7-2 ur because you read the array from a[0] not form the last p/s : sorry if my english is bad

[@Qwerty_945]

why not x = 7 and y = 2 ?

[@varaddeshmukh1137]

i am trying to sort ' ' ' float array[5]= {11.1f, 11.34f ,11.22f, 11.99f, 11.00f}; ' ' ' it won't work in qsort why? any solution if i want to sort float using qsort?

[@PortfolioCourses]

Good question Varad! :-) qsort() should work with floats, so it makes me think something else is happening in your code, or maybe how qsort() is being used.

[@varaddeshmukh1137]

@@PortfolioCourses is there any way to sort float using qsort()

[@PortfolioCourses]

Yes, the 2nd post here has an example: cboard.cprogramming.com/c-programming/1293-qsort-doesnt-work-floats.html. :-)

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THANKS

[@PortfolioCourses]

You're welcome! 😀

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beautiful

[@PortfolioCourses]

Thank you Tristan! :-)

[@tristanhurley9071]

@@PortfolioCourses No worries! Quick question: I am trying to order an array of structs by their Age. In your example when calling the qsort function you use "compare" as the last argument, but why do you not need to provide two inputs (x and y) into your compare function? Yours runs with just 'compare'. Apart from this, I think comparing the ages within the structs should be straight forward?

[@PortfolioCourses]

Great question. :-) So it's actually the *function* compare that is being supplied as an argument, we're not actually *calling* the compare function there so we don't supply arguments to it. The qsort() function will "have" the compare function as a parameter now, and *it* will actually call the compare function with different arguments to sort the list. And comparing ages within structs should be pretty similar. You'll need to some kind of different casting here though I suspect: int x = *(int *)x_void; int y = *(int *)y_void;

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[@ahmet8266]

Thanks man i copied all of it

[@PortfolioCourses]

You're welcome Ahmet! :-D

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Hahaha… :-) images.app.goo.gl/kAaYgj9HLikh6HrN6

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