How to write your own code libraries in C.
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- เผยแพร่เมื่อ 20 มิ.ย. 2024
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Website ➤ www.jacobsorber.com
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Welcome! I post videos that help you learn to program and become a more confident software developer. I cover beginner-to-advanced systems topics ranging from network programming, threads, processes, operating systems, embedded systems and others. My goal is to help you get under-the-hood and better understand how computers work and how you can use them to become stronger students and more capable professional developers.
About me: I'm a computer scientist, electrical engineer, researcher, and teacher. I specialize in embedded systems, mobile computing, sensor networks, and the Internet of Things. I teach systems and networking courses at Clemson University, where I also lead the PERSIST research lab.
More about me and what I do:
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![[Day 16] - Static and Dynamic Libraries (ar, objdump, ld, ldd) - Crash Course in C Programming](http://i.ytimg.com/vi/YtiPCPtmZrs/mqdefault.jpg)
this video saved an intern who's new to the cross compilation world.
Kids these days have it so easy. 20+ years ago if you lived in the middle of nowhere you'd be lucky to find a compiler on floppies, then never find compatible books. It took software piracy and haggling with an alcoholic college dropout living in a camper to score a copy of Borland Turbo C v2.04 AND a highly used copy of Waite Group's Turbo C Programming for the PC by Robert Lafore... That book never stopped smelling like a tool shed.
Your short C vids are fantastic! Especially ones on more complex topics.
LOL
🤣🤣
okay....boomer. Forget your pills?
This is brilliant, thank you. Would be a nice intro to a larger video on dynamic code loading at runtime.
It would indeed. Stay tuned. :)
check th-cam.com/video/_kIa4D7kQ8I/w-d-xo.html
4:13Thank you, this is something that I don't think is explained in many tutorials for setting up dynamic link libraries and was very confusing for me.
Dude 🙏 this has been so informative, can express enough how grateful I am. Not only have I learned a bunch about creating libraries, I also learned a bit more about using makefiles. I use gcc and was relieved that I didn’t have to change anything.
Again, much thanks.
Your videos are awsome. straight to the point.
Helpful video, thanks!
I literally had to pause the video to comment. Thank you Sir Jacob for educating the masses with such sheer brilliance!
Amazing content. Thank you so much!
thank,omg I was pretty sad for don understand the libraries in C , thanks
really good explanation, thanks.
Very nice! Thank you!
Heyyy, you should try to make a video on how to make your own data structures or the thought process behind it. That would be super cool
Excellent video! Thank you!
Welcome. Glad you liked it.
Thank you so much for this!
Very helpful. I knew how to do this stuff with Visual Studio on Windows, but there wasn't a whole lot of stuff about how to do this stuff in Linux.
Thank for your explanation!
Please, consider to talk about Autotools in some next video. Thank you again.
Me: Tons of information in 10 minutes?
Jocob: YES! Damn it..
your the best c teacher i ever seen
three months ago, this video would have saved me some hours!
can you do a video about dynamically linked libraries?
Do you mean DLLs on Windows? The .so files from this video are dynamically linked libraries. They just aren't called DLLs, but they are basically the same thing.
I meant the dlsym family of functions. I had to use them once in a class excersize, but I never really understood their use.
@@benjaminshinar9509 Ah, yes, that's on the docket for the coming months.
Gracias Jacob
A lot of that information went right over my head. That was very fast for an AP CSP student, who just started using C in August.
You can always watch them at half speed, and I do have some more beginner-focused videos. Let me know if you have specific questions.
I just stumbled on your channel a few months ago. The content is fantastic!
Regarding adding a shared library to a directory in the ld search path (or even a symbolic link to my library in, let's say, /usr/local/lib), don't I also need to do 'sudo ldconfig' to update the linker's library cache?
Thank you very much for these great tutorials! Very useful and good explained.
I have one annotation to your code: The identifier __MY_CODE_H__ of your "include guard" may clash with identifiers of the compiler implementation. (For this identifier it is unlikely.) The C standards specify that certain identifiers are reserverd for the implementation, particularly those with two underscores. So, you may better want to use just MY_CODE_H for this purpose.
Thanks, Micheal. Yes, a few people have pointed that out, as well, down below in the comments. It's always nice when you teach me, as well. :)
@@JacobSorber You are welcome! - This is one thing, I also learned long after my studies. And though I know C for several years, I am still astonished that there a language features and concepts I have not heard about before. Stay healthy, blessed holidays and best greetings from Germany.
The searchpath for the runtime liker can be mangled during compilation as well.
You basically have to link your executable like this (untested):
gcc -o bin *.o -Wl,--rpath="$ORIGIN"
This will make the runtime linker look in the same directory as the executable (this behavior is as far as I remember default on windows).
Great video...
Awesome video.
WoW .. genius ....perfectly wrapped in 10min video.
Note that in your header your include guard starts with two underscores, and I believe that violates the C standard as those are reserved
Ah, good catch. Yes, should have _MY_CODE_H_. Thanks.
@@JacobSorber that's still a reserved symbol by C, any identifier starting with an underscore followed by a capital letter is reserved
@@JacobSorber uh uh uhhhhh, you forgot the magic word! (jurassic park reference)
If I wanted to make a non-destructive version of reverse. Is is advisable to create an additional array in main() and then pass its address to reverse so that it can save the reversed string, or is it better to malloc on reverse and then return that pointer to main()?
I was calling my library header.a, and I wasted hours trying to make the linker find it, that was until you mentioned the lib- as (libheader) detail, thanks!
thanks !
I love you man
4:08 Why is "-l" needed during build time? Doesn't that beat the whole purpose of shared libraries? Why not just use static libraries if both need to be present at build time. I would expect to be able to build my main program without specifying ANYTHING about the shared library, otherwise it's not really dynamic.
The name dynamic linking is due to the fact that the .so file contents aren't embedded into the executable at the time of compilation. They are loaded at the time of execution(Dynamic Loading). So the size of executable is smaller than a statically linked library, which has library code embedded into it.
Now suppose u have a function with the same signature but different internal code in two different libraries. The -l flag will allow you to specify exactly which function to use.
Also you would not like it if you tried to link to a shared library if you did not need it, right? Like math.h need -lm flag to link it, without math.h we wouldn't need -lm flag.
Hey Jacob great channel!, maybe you can point me in the right direction, here it goes: I have this elf executable, a game server, which loads a .so file which is the game skills library, it contains every skill the game uses. I don't have the source code and I want to add new skills to the game, is viable to write a new elf .so library, include it together with the original, and write new skill functions there??? will it work? will the second library have access to the original library functions??
How do you claim the data location of the pixels of the screen or use the gpu?
Awesome video. I was curious why using -rpath wasn't suggested as an alternative way to load the correct .so at runtime?
Thanks, Ken. Limited time. Each video can only cover so much. I'll add the rpath option to the future video topic list and see what I can do about it.
Thanks, I learned what I needed to know! What will actually happen if I put the function code into the .h - file? I read this is not allowed.
You're welcome. You can put function code in the .h file, but it's discouraged because you often run into odd issues when multiple files include the same header. You can easily end up with multiple versions of the same compiled function with the same name in different object files, which causes problems when you try to link them together. So, keeping function code out of headers will help maintain sanity.
what is your opinion about rust ?
.. is it good a new inovation replace for C duties ?
can you talk more about dll files in windows?
how system knows which lib to load for specific symbol?
So what would be the difference with using the s flag on ar and running the ranlib command after making the library? I was taught to use ranlib and I hadn’t noticed the s flag before.
is there a way to treat a shared library as a static library at compile/linking? I assume there may be some issues with license rights, i don't know if lgpl treat static and linked libraries separately. assuming I have the rights to share a library how i feel fit. ( i wrote it) and i want to share a program i wrote (using this library) with someone. say i want to do this to have them test a user interface, but don't want them to have to install my library. I just want to send them an executable. if i have the code on my computer i can just include it at compile time, but lets say for some reason this is not possible. sorry for the drawn out question
Where did you run this whole thing like is it visual studio code or what ?
I gave you the 100th like.U r awesome.
Thanks!
s means subscript. Sometimes this word is interchanged with index. Maybe inherited from math language.
Thank you so much for this video! Not enough teachers really spend enough time on this topic
is there a need to make the reverse function exposed?
please keep upload videos about c in deep technichal level
Is there a curriculum for the course somewhere ?
Awesome. Why do we have to mention -lc in case when we are building .so and not in static library case or .o recipie
Hey, did you figure out why?
i don't understand at 8:51 when he says that "the bigger static version doesn't need a library anymore, all the code is inside of it so i can just throw the library away at this point and the static binary is still gonna work just fine"; what file/s can be thrown away? the .c ? and what does he mean by "satatic binary"? is it the same as the .a file? can anyone please clarify?
in windows cmd, type "set _env_name = "_path_" "for setting temperorarily setting environment variable.
for permanent setting use "setx" instead of "set"
Can I use .dll instead of .os is that enough , can I able to create dll
nice one, btw what does -g flag means?
"Just add al this, no need for explanation what all this means you're here to learn after all"
very nice. so much content in 10 mins
nice video jacob sorber,
Thanks. Glad you liked it.
:) Ok @@JacobSorber
what do you mean by position independent code ? What could make a code dependent of it's position (other than data alignment that i don't think is the case in this example)
Compiler's often generate code that uses fixed addresses for variables. This can result in slightly smaller and (maybe a little bit) faster code. That code can't be moved to a different place in the address space and still work. en.wikipedia.org/wiki/Position-independent_code
Is there a reason why you put the #ifndef __mycode_h_ and #define _mycode_h in the header file? The whole code works without it as well.
Are there any good general use libraries that others have made? General use as in libraries that most people would find useful.
Yes, there are. en.wikipedia.org/wiki/Category:C_libraries
Oooooooh I get it now.
what is the name of the program that you use?
and i had learnt C but didn't learn data structure so when i looked at the code i didn't understand some codes like
what is this page that you opened and typed clean and there were the name of the library. o
and what is this language that you use to write in this page?
this page name was
'makefile'
the same name of the project
how do you opened it
hey Jacob, I used a lot of excel, vba & C. What would be a good way to send data from excel to C program? I would like to use excel sheet for input as I dont have to work on creating an interface. Then I think my excel would generate a text input file for C to take as input. But is there anyway the process could be improved without creating an input file for C. Thanks
I don't do a lot of excel programming these days (ok, almost none). So, I'm just guessing here, but I would look at what sort of inter process communication options excel's VBA engine allows. I know they allow database connections (may not be more convenient than a file), but maybe they support other things like sockets, which might be simpler.
@@JacobSorber I went through some articles on the internet, they support dll library, So I am thinking I could make dll libraries and use C functionality from excel.
Hi. I haven't programmed in C since the 80's but looking at it again for some raspberry pi projects. Your videos are a great review. Is there any chance that you have some of the code samples available for download? Thanks for you great work.
Any suggestion for book|resource about "make, MakeFile, static|shared libraries"? (not including dev dox)
What are you wanting to learn about them?
@@JacobSorber something that would be suitable for web|mobile application layer developers, or newbies, with not being purely focus on coding
* process steps from source to executable(ex: with GCC from CLI)
** preprocessing step
** compilation to assembly source
** compile to object
** linking
* compiling multiple files
** how to write make|cmake
** use cases on when to compile to shared object or static library
** how to compile when changes are on single lib file, not whole project
** mechanism used while compiling, such as caching, etc.
** why not write everything in header file, proc|cons (ex: build time perf.)
** how to write makefile for example, one library can have multiple files
** src/
*** main.c
*** lib/
**** queue/
***** queue.h
***** queue.c
***** node.h
***** node.c
**** bitmap/
***** types.h
***** bitmap.h
***** bitmap.c
** how to include external C library (ex: libexpat)
* basics of debugging (gdb, lldb)
BR,
Ivan Zvonimir Horvat
Maybe try this one. www.amazon.com/Advanced-C-Compiling-Milan-Stevanovic/dp/1430266678/
@@JacobSorber Looks great, thank you!
8:03: "Why s is for index, I have no idea."
Perhaps it might be related to nm(1), where -s is for [s]how archive index.
s is for symbol index.
@@pippinpiggeldipi4144 Thank you!
Then how can we see what is inside library like math.h or studio.h .???
At 1:11 you could of also just used "#pragma once" to make your code much more neater and easier to understand.
Hi Jacob, I made a linked list library, having functions such as addToBegin, addToEnd, removeFromBegin, removeFromEnd, and want to realize STACK based on it, the STACK has APIs like push and pop which are just wrapper of addToEnd and removeFromEnd. My question is are there any ways that I can stop STACK from calling addToBegin and removeFromBegin.
I'm not sure I understand what exactly you're trying to do. Are you trying to prevent function calls, without changing the code that makes those calls?
@@JacobSorber Thanks for your reply. I want to implement a Stack data structure based on LinkedList. But when I include linkedlist.o, it can access all the APIs of it. here I only want to expose some of the APIs of linkedlist to Stack. Sorry, English is not my native language, and the question is not very clear without showing the code.
I see you are tackling very interesting subjects. Wish there were channels like this 10 years ago when I first learned pthreads and shared libraries. When I made my first and only lib. I'm working on another, so that's why I'm refreshing my memory.
Anyway, I'm very intrigued by your editor. Seemed to me at start to be gnome builder, which I recently became accustomed to, or that other one "Atom" which I heard you mention in another video. Looking at atom screenshots on google images, it is very very similar in looks with builder. But it's 300 megs. And has a dependency on electron which in turn has a dependency on openssl 1.0, which... cannot happen in a sane gentoo environment. would be a nightmare to use openssl 1.0 at this point. is one year old and broken. would break every other program that uses openssl. shame... the highlighting seems exceptional. i've been using vim, emacs, and they work fine for interpreted languages. not so much for c. I recently discovered gnome builder, which is my favorite by far, as it keeps track of a lot of things, (next release it will also do git for you), but it's still not exceptional. it has minor annoyances. key shortcuts that are missing maybe. having to use the mouse more than I'd like to. but mostly highlighting. especially for C. builder keeps track of symbols, for if you have a header where you define a function, and that becomes a symbol, builder will keep track of that, and highlight it. there a search function in the upper right part of the program, which allows to search in all the project or, symbols which are read in headers. very useful. i'm not sure it keeps track of what you might call "global" variables, and that is one of the annoyances. on the other hand doesn't depend on electron which has 700 megs itself, + 300 megs the editor. only normal gnome stuff. nothing special in the dependency department. kinda small and light. so... pick your battles. still, very nice looking editor that atom.
see, atom highlights even integers. like real hardcoded integers. like the frame at 1:30. it highlights 0 and 2 and 1 twice. which are numbers hardcoded into your program. which is nice. but on the other hand it uses the same color for i and len and string and temp and all the parenthesis and stuff. and operators are the same colors as some of the declarations. so, again, pick your battles.
I can't find an editor that completely satisfies me when it comes to C. But I think it's me, not the editors :)
Yeah, it's an endless struggle. I'm currently using VS Code, because it's not as sluggish as Atom, but seems to provide most of the atom features that I like. I guess this must mean that I'm starting to forgive Microsoft for the 90s. :)
Can u show or say how can we read or look into a library like math.h or studio.h or openGL etc what and how do they write those functions in it like sin() function from math.h library
@@JacobSorber Can you pls share the link to the playlist on "How to create code librairies"(that's if you do have),I'll really appreciate🙏
I wonder what would happen if you typed ./static_librarytest "otavol imed" instead of ./static_librarytest "OOps"
*TLDR: Why static libraries?*
I have seen many standalone projects using self written static libraries... what is the benefit of static libraries in this case?
prototyping libraries, or in other words designing what functions do what, what the library's purpose is, etc. is often done with compiling & linking the library statically, as using shared objects/dynamic libraries often takes a little bit of more work. It is just for convience
If the code object is internal to your project then link statically. That LD_PATH manipulation he uses is a maintenance and security problem.
1:57 can anyone explain why there is no trouble with ‘\0’ this guy? If I’m not mistaken his function returns a pointer to a non null-terminated string and then he just printf’s it with a simple %s specifier…
Does using a library make me less of a programmer if I rely on them too much?
No. Well, if you're using them to avoid learning new things and extending your own abilities, then I suppose you might be stunting your own growth. But, in general, I think using libraries to avoid extra redundant work is a great thing.
1:34, uh, I woulda just used 2 indices:
```
for ( i = 0, j = len - 1; i < j; ++i, --j )
{
char tmp = str[i];
str[i] = str[j];
str[j] = tmp;
}
```
much easier to read too
what is "-L ." doing if the compiler won't search the current directory even if it's used?
Shared libraries are linked twice once during building the code which is when the “-L .” takes effect. The second is at runtime by the dynamic loader. The second time needs the LD_PATH variable set.
@@Knirinahh got it
It's all fun and games until you try to add wininet library as a static library and then mingw's ld.exe complains with a series of undefined reference errors even when all the Ls have been provided in cmake. Any ideas?
libmycode = -lmycode, not supported in gcc
how can you compile if you don't have an int main() ??
It's really the same. *main* is just a function that we've agreed to use as the standard program starting point. But, you don't run a library. Programs load the library and call its functions. If it had a main function, that would be really confusing. I mean, which one should we run when the program starts?
@@JacobSorber Thank you bro
what ide?
1:10 why not "#pragma once"?
Very clear and focused video. It is amazing how efficient your video are. If I had to explain it I would digress infinitely.
Also it's a bit technical I found th-cam.com/video/JPQWQfDhICA/w-d-xo.html on the dll stuff, which is... kind a trickier than Linux, I'd say. I am not very fond on the way C is treated by Windows but never know, it is always interesting to see something different.
I still haven't seen all your video but I'd love to see how you would explain ABI.
Cool. Thanks. Is there a specific ABI you're interested in?
Your ls is not set to "ls -lrt", which is very confusing...
Sorry that confused you.
WHY DISLIKES!!!!
So i did not understand most of the stuff he did .... Specially with make file... I hope i need some prior knowledge... Can anybody tell what do i need to learn before being able to understand this content completely?
I'm not sure what exactly confused you, but you might want to check out my make videos.
5:27 spoiler. no, it still wont find a library
Hey Jacob you are really fast typer. But this makes me not to understand some code or steps. So I suggest you to explain it little slowly.
Too much fast for a beginner
牛逼
Nice rapping
anyone build a networking library for c yet ahah its really not funny we cant let c die its historical and plays a big role in our present. it was made so long ago (1978)
we need window libarys
i mean its worth the work of prob needing to make a driver
There are a lot of C networking libraries. I'm not sure what you are specifically looking for. And, I wouldn't expect C to "die" any time soon. It's the foundation language for so many other things. Rust has gained some steam lately, but it's got a long way to go to replace C(/C++).
@@JacobSorber I found that the cygwin package has networking sockets but I was hoping to find a library with websockets
Sorry, but still I don't know
Why don't you get it, at the end of the month, you'll be worth nothing.
That's his favorite saying to me, because his value is tied exclusively to his bank account. Fine, bankrupt him.
You are too fast though...
you talk very very fast