strtok() function | C Programming Tutorial

[@felixobianozie3745]

Concise, yet a complete guide to using strtok. I never knew the function had a polluting effect on the original string buffer; I have never actually had need to look at the original string buffer again after a strtok() parse. Thank you!

[@PortfolioCourses]

You're welcome Felix! :-)

[@fifaham]

I like to watch your videos and immediatly find practical use for them. Great video Kevin.

[@PortfolioCourses]

Thank you! :-)

[@wheatdaddy_9629]

Thanks for this video. I'm working on rebuilding some of the standard libraries in C, and this one was more difficult to find a good explanation on. Much appreciated!

[@PortfolioCourses]

You're welcome! 😀 I'm glad to hear it was helpful.

[@PortfolioCourses]

​@@Trash7Trash7Trash7 hopefully this one helped! 🙂

[@PortfolioCourses]

@@Trash7Trash7Trash7 You're welcome! 😀

[@theworld-zr5jp]

Became a big fan of your concept explanation sir, really appreciated, loved it..

[@mllllll1211]

this is some really good step-by-step explanation

[@PortfolioCourses]

I’m glad you enjoyed it! :-)

[@cchriz4292]

a short yet very detailed and helpful video!

[@PortfolioCourses]

I'm glad it was helpful for you! :-)

[@HeavyMachinery512]

I was reading a book where I saw this strtok() function. But in the book it was not explained really well. so I turned up here and really have got basic understanding of it now. Brilliantly explained . keep up the good work!

[@PortfolioCourses]

Thank you Muhammad! :-) I’m glad to hear the explanation was helpful!

[@juliuskamara1348]

@@PortfolioCourses This video is really amazing!

[@Rain663]

Very well explained! I was wondering what that "NULL" was doing in the example code I'd found.

[@PortfolioCourses]

I'm glad you enjoyed the explanation! :-)

[@amanimavu810]

Thank you. Helped me know the problem in my code. That part of adding null bytes at the end of every section, is really important.

[@PortfolioCourses]

You're welcome Amani! :-)

[@kishorbabu9129]

Thank you for providing information in KZbin now a days KZbin became as knowledge hub ... thanks sir

[@PortfolioCourses]

You're welcome Kishor! :-)

[@DataAnalyst-r6g]

This is the best explanation of a function

[@mastermax7777]

i really like the dive deep portion and thinking beyond just the basic functionality. starting at 9:00

[@spring-tp6dr]

Very good explanation. Heaven send gift to C students!

[@PortfolioCourses]

Thank you! :-D

[@user-kv4gj9jp4h]

You explain everything so well thanks

[@PortfolioCourses]

You're welcome, I'm glad you enjoy the explanations! :-)

[@Ajamtroye]

Ok i made a strdup to a an other strings but i don't find how can i then free the string

[@lordmortymer]

Awesome explanation. Will be avoiding this function as much as possible now lol

[@PortfolioCourses]

I'm glad you enjoyed the explanation! 🙂

[@aryamansrivastava1816]

amazing videoo..cleared the entire concept to me

[@LapCreativeStudio]

sir thank u so much for your explanation thank u love your efforts

[@PortfolioCourses]

Thanks so much for sharing this, that’s awesome to hear you enjoy the video! :-)

[@normanweiz2646]

Thanks for your great explanation. That was very clear and easy to follow. Well done. I have always had difficulty understanding strtok. I had a thought while watching your explanation. What if you had some numbers in the string and you wanted to retrieve each number and assign to separate variables? Could that be done using the while loop or is it better to do that manually as you did using the *portion?

[@PortfolioCourses]

Thank you Norman! And it sounds like that could be done using a while loop, which would be useful if you don’t know how many numbers there are in the string. But I think either approach could work ok too!

[@Henry-sv3wv]

if you want to assign into an int then you still need to convert the string: char str[]="12"; int val = atoi(str);

[@zhaoaverie2256]

Thank you so much for the awesome tutorial!

[@PortfolioCourses]

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

[@PasanKarunanayake]

Superb explanation.👍

[@PortfolioCourses]

I'm glad you enjoyed it Pasan! :-)

[@amanwehib8367]

Great explanation! Thank you very much.

[@PortfolioCourses]

You're welcome Aman! :-)

[@SlideRSB]

Why did you end up with two null terminators at the end after the tokenization?

[@davidverheyen6635]

Thank you, chars confuse me less and less. What would be the best way to use a delimiter that is 'unprintable', like STX (ascii value 2).

[@decibi2684]

Hi Sir, Could you please make video on how to implement our own strtok function ? Thanks in Advance.

[@azarelgrahanditoadi7507]

thankss for the explanation! this is the way.

[@PortfolioCourses]

You're very welcome Azarel! :-)

[@neilanpadilla]

just wanna ask, do you guys use this ' * ' for memory allocation?

[@jess-inspired]

Hello sir. Read that strings in c cannot be modified yet strtok modifies the original string. Was thinking it would return a pointer to a new string on the heap. So please can you explain how this truly works under the hood?

[@PortfolioCourses]

Strings in C *can* be modified, so that's essentially how it's working, strtok() *is* modifying the string. 🙂

[@jess-inspired]

@@PortfolioCourses Thanks a lot sir.. Let me show you a code I've been having issues with lately.. Code 1: works well..' a' is modified to 'k' int main(void) { char str[] = "abcd"; str[0] = 'k'; printf("%c ", str[0]); return 0 } Code 2: segmentation fault int main(void) { char *str = "abcd"; str[0] = 'k'; printf("%c ", str[0]); return 0 }

[@jess-inspired]

@@PortfolioCourses Not really sure, why the second isn't working..

[@PortfolioCourses]

@@jess-inspired Oh that's a tricky one, basically in the 1st example a char array is created to store the string. In the second example, s becomes a pointer to a 'string literal' stored in a read-only part of memory where modifying them is not allowed by most compilers (the C language definition leaves the exact behaviour as 'undefined'). So if you want to create and initialize a string that you want to be able to modify, you need to do it the first way. The second way does create a string that is a sequence of chars ending with a null terminator '\0', BUT it will be 'read-only' in that case. And you know what? This is a FANTASTIC idea for a video haha... I think I might make this video soon explaining this difference because it's definitely confusing! 😀

[@jess-inspired]

@@PortfolioCourses Wow! That would be great. Encountered this issue while trying to write my own strtok function.. Thanks a lot sir, it's an honour..

[@dimitriossomarakis3946]

what if the message is numbers, for example:"22-33-22-44-63-66" and I want to take a couple of them every time. how can I proccess the numbers after that. for example to push 22 into a variable that is type integer??

[@PortfolioCourses]

Great question Dimitrious! You could use atoi() to convert the string into an integer: cplusplus.com/reference/cstdlib/atoi/. I have a video on that one: kzbin.info/www/bejne/i4KynYeadtd2iNE. :-)

[@dimitriossomarakis3946]

@@PortfolioCourses I think I also can do that with strtok function in order to keep the 2 digits and after that I can use sscanf to convert it into an intiger. What do you think? Thanks for responding!

[@PortfolioCourses]

@@dimitriossomarakis3946 Yes, I suspect sscanf may work as well. You may even be able to just use sscanf from the start and not even use strtok() at all. Maybe try a format string like "%d-%d-%d-%d-%d-%d" to read in 6 ints separated by - chars? 🙂

[@dimitriossomarakis3946]

@@PortfolioCourses yeah I will try , thanks man

[@silentcal275]

What is in your string.h and studio.h files?

[@mastermax7777]

a question, how is it keeping track of how far its in the string? what if i call another strok. what if i call it again using s instead of NULL?

[@lukeherbst7931]

If you call it again using S, it will start over from the beginning

[@1kvolt1978]

Probably, it just saves the last used pointer in static variable.

[@notebook2866]

best tutorial ever

[@PortfolioCourses]

Thank you very much for the positive feedback! :-)

[@sasindudilshan6679]

thank you very much sir !

[@PortfolioCourses]

You're very welcome Sasindu! :-)

[@dimkayilrit2606]

Great content

[@PortfolioCourses]

I’m glad you enjoyed the video Dimka! :-)

[@happytime3042]

Thank you Sir 😊

[@PortfolioCourses]

You’re welcome! :-)

[@fifaham]

This code works to extract the password, and others, inputed from streaming data of mobile phone: char s1[30] = "@P123456@D254@X232"; char d1[4] = "@P"; // Password 123456 char d2[4] = "@D"; // Deactivate 254 char d3[4] = "@X"; // Activate 323 char *portion1 = strtok(s1, d1); printf("The password is: %s ", portion1); // works nice I will try to implement in my project. Thank you Kevin.

[@PortfolioCourses]

Thank you for sharing this! :-)

[@codingprogramming9510]

Thank you sir for this amazing channel I really benefit from it a lot! keep the good work going! Sir i have a question a bout this command line: (inside the while loop) portion = strtok(NULL, d); Q1: what exactly happen when the loop reach this line? I didn't understand very well how this line work... if it first argument is NULL why the loop keep going? shouldn't it stop after the first delimiter it face, because this delimiter will be NULL, I don't know if you understand what I meant, but it will be helpful if you can explain to me what happen in that command line, I will really appreciate it. [i am still learning :) C language ] Thank you.

[@PortfolioCourses]

I'm glad to hear you enjoy the channel! :-D So the strtok() function is a bit special, because we call it multiple times for each "portion" of the string, and we call it differently the first time compared to the subsequent calls (for the same string). So the FIRST time we call strtok() above the loop we *do* give it the string s as an argument (and delimiters are the 2nd argument d): char *portion = strtok(s, d); And then inside the loop, in the subsequent calls, instead of s we call it with NULL as the first argument: portion = strtok(NULL, d); This is a signal that tells strtok() to "keep using the same string that we previously passed in". So even though we are passing in NULL, strtok() will continue to use the string s from the previous call. And it will try to find the *next* delimiter in the string from it's previous position (where d is the string of delimiters). "On a first call, the function expects a C string as argument for str, whose first character is used as the starting location to scan for tokens. In subsequent calls, the function expects a null pointer and uses the position right after the end of the last token as the new starting location for scanning." ^ that is from this documentation of the function here: www.cplusplus.com/reference/cstring/strtok/

[@codingprogramming9510]

@@PortfolioCourses Thanks a lot Sir, now I understand it well. Really appreciate it.

[@PortfolioCourses]

You’re welcome! :-)

[@ShubhashChandraYadav-e2w]

Thank you sir

[@nerd6134]

Nice 👍

[@PortfolioCourses]

Thank you! :-D

[@cryptotechcoder]

Very awsome

[@PortfolioCourses]

I'm glad you enjoyed it! :-)

[@cryptotechcoder]

@@PortfolioCourses I'm glad you made it

[@krish-ut9de]

Thank you very much sir

[@Ak-zm3ce]

great

[@dwadwadw8730]

thanks

[@PortfolioCourses]

You're welcome! :-D

[@dwadwadw8730]

@@PortfolioCourses can you print all the delimited strings in a new matrix and then sort them aphabetically

[@PortfolioCourses]

@@dwadwadw8730 With some dynamic memory allocation, string copying, and a sorting algorithm, that's definitely possible. :-)

[@abdurraheem2444]

best

[@PortfolioCourses]

Thank you Abdur! :-)

[@ryanalnaser914]

whatever anything

[@PortfolioCourses]

I don't know if this is a question or not. :-)

[@stathislourantos1194]

Very good educative video. One question though: How would I split a text using multiple delimiters? Let's say, taking your example, how would I get rid of the final dot after the word "way"? Or, if the text was: "This_is: the way! folks...", how would I split the text ending up with only the words? This is the way folks

[@1kvolt1978]

Write your own function obviously. Because this is exactly how it works in programming.

[@vishwaravi45]

thanks ❤

[@mimicmian]

THANKS

[@PortfolioCourses]

You’re welcome! :-)

[@Local_Nerd]

Thanks

[@PortfolioCourses]

You're welcome! :-)