Header Issues: Guards, Name Mangling, and extern "C"
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- เผยแพร่เมื่อ 7 เม.ย. 2019
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Header files often have things in them that confuse beginning programmers. This video explains two of them - ifdef guards and extern "C" blocks.
Objdump video: • How to Inspect Compile...
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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:
www.jacobsorber.com
people.cs.clemson.edu/~jsorber/
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6:44
_Z prefixes all Itanium mangled symbols to make it abundantly clear that the symbol name is mangled, else certain names (global variables) can be impossible to tell if mangled or not.
7 is the string length of "getmean"
Capital P is short for pointer, i is short for int, d is short for double.
that makes so much sense!
In your videos every aspect of C programming looks so clear and straight forward - in my C code things just segfault and dump... :D
Wow! It really makes me stand in awe to see how well you can explain stuff and cram this much of excellent content into one succinct and beautiful video.
Congratulations!! 👏🏻👏🏻
Thanks, Leandro. Glad you enjoyed it.
@@JacobSorber gcc-compiler is aliased to clang-compiler in the mac
the manual page of gcc (it doesen't exist)
see this: % gcc --version
Thanks for this video Jacob, I understand now the used of header guards. 😊
Your videos are so great! Thank you for your work!
Thanks, Renata. Glad you're enjoying them.
Unbelievably useful and EASY TO UNDERSTAND.Bit respect,sir
Millions and millions of thanks for such a beautiful explanation in such a short video. Never heard "Name Mangling" before.
Please keep up the good work👍👍
You're most welcome.
Excellent delivery and a great topic for C, C++ and Objective-C compilation
These are amazing videos! keep up the good work!
Very much informative, loved it!!. Keep making more like this.
Awesome explanation. Crisp and precise! Thanks.
Thank you very much, this is the best explanation i have seen, if you understand a concept you will never forget. Well explained. Thank you
I know it's not common, but I always indent #ifndef, #define, #endif etc. Makes the code a lot easier to read right away. I can't see why one should not indent these guards. Jacob, thank you for such great videos. :)
Sometimes when you are dealing with a huge block of code, not indenting them makes the code a little tidier.
if the ifs are on the start and end of file then no, but if it's inside a function then I do indent
Because older C preprocessors didn't recognize the "#" at the start unless it was the first character on the line.
I actually do not indent them because they are not part of the code flow, and often, as said encompass large section of code, if not the whole file
besides a college course on C++ i don't think i have used function overloading. I had assumed that both C and C++ both supported it. this is the problem with taking a C++ course with out a C course or a C++ course making the assumption that the student will only use c++ and never C. thank you i learned something new today
The most perfect video on the subject
Wow thanks alot! Stumbled about an issue on a large mixed c/c++ project at work today where the name mangling causes some errors I couldn't explain in the first place. Then a colleague told me about the name mangling and this video came in really handy!
Great explanation! Thanks
Well I think you are realy onto the best ways to teach programming teaching the real fundamentals you actually need to move on explaining purposes and showing why some parts necessary in a subtructive manner good job help spread this so needed teaching model!
awesome explanation with in less time. thanks a lot Jacob 😊😊😊❤❤
My pleasure! Glad it was helpful.
This is a great place, u got a new subscriber
Yet again an excellent explanation
Thanks for the information. Keep uploading new videos.
Awesome explanation! Thank you so much!
Hey, I've been loving your videos, do you have any explaining "extern inline" and percompiled headers?
Beautifully explained.
Wow! I read it a lot but never understand it until I found this video. Awesome. Thank you.
You're very welcome!
Two days ago I was trying to test my C code with Boost testing library, but I gave up without understanding the reason. Now everything makes sense :D Thanks
Nice. Glad it helped.
thank you for this great video
Hey Jac, simple is awesome. Nice video.
Thank you sir, please don't stop creating good contents like this
I'll keep doing what I can. Thanks for watching. Please spread the word.
@@JacobSorber I really will (~_~), Thanks
6:51 This is just a guess, but I believe the __Z17 in print_person_info and the __Z7 in getmean represent the length of the original function names 😁
Thank you, Jacob☺️
great video. won my subscription fair and square
Awesome. Thank you
5:57
a) The return value is NOT part of the function signature
b) "arguments" are not part of the function signature - parameters are (arguments are "instances" of parameters)
Being painfully careful about clear communication is key in CS, especially when teaching beginners
a big wow!!!! amazing!!! i paused the video hit like and subscribe and the resumed the video!!! Thanku so much for your contribution, through youtube
Hi Jacob! you're so great teaching C code. I love your videos!!
I've been working with java (more recently kotlin) and android for 4 years now. The thing is that I'm tired of it and I definitely want to try smth different. I'm looking for C and Rust as languages of my interest, so can you please give me some advice about what should I do to start getting my hands dirty and learn real world C code??
Thank you so match and keep the great work :)
As always top content
Useful information
plz next video on Linker how it work... and able to figure out and connect code in libs to our code ??Thank you for these amazing video i learn every time new from these videos.
Thanks for the request. I'll add it to the list and see what I can do.
One thing you could touch on is why some header includes have a forward slash in them -->
That's cool. Thank you !
You're very welcome.
Great video and subject.
I found out about extern C when creating a DLL to be used by LabVIEW, an interpreter. The same issue would exist with any extensible interpreter, imagine VBA and Python calling DLLs written in C++.
Actually it IS possible to call C++ code from within Python, in fact there are multiple ways of doing it.
Thank you. 👏
You're welcome.
I love your channel :)
Thanks.
hey hey:
gcc is aliased to clang in macOS
try the manual page of gcc (it doesen't exist)
brilliant
so basically it makes the getmean() function not "depends" from the rest of the code and can therefore be used as a dynamic library?
I've created some code that does that but to explain it, well it's hard to find any explaination.
Sir can you make a video on parser and it's types .how to make a simple parser but not the compiler parser
Yeah, probably. What do you want to parse?
You can't overload by return type alone on C++. The parameter lists (perhaps after a bit of meta/SFINAE stuff) must be distinct.
1:53, yeah I don't normally use extern C directly, instead I just set a few macros like so:
#ifdef __cplusplus
#define LINK_C extern "C"
#define OPEN_C LINK_C {
#define SHUT_C }
#else
#define LINK_C
#define OPEN_C
#define SHUT_C
#endif
Then just use 'em instead, less code overall
I've download an open source project I want to work on called Treesheets. All the code is in the header files. I've modified some of it and added new features. BUT I still cannot work out why the heck he put the code in the h files. Will be looking into it so I fully understand it. There has to be a reason. He works for google and knows what he is doing. I may email him if cannot find out myself as he is open to emails, but want to research myself first!
You ever find out?
please i am looking at learning a language that is multidimensional as in can let me cut accross robotics,arduino,software,embedded systems etc without being limited but will love to know te best language to learn
Some of my thoughts on languages can be found here.
th-cam.com/video/wcpH2PkC-94/w-d-xo.html
Instead of standard header guards, you can just use #pragma once. You don't need to worry about duplicate guard names, and it is a bit cleaner looking. It is possible if you use symlinks, it can fail, but compilers also check for filesize, hash, etc so it is unlikely.
Also... C doesn't support overloading? Didn't know that.
#pragma once isn't part of the C standard, so it may not compile on some compilers. Compiler-dependant behavior isn't a good thing.
I have a question let’s say we have a project . When do we use c and when its c++?
can you please explain to me the relationship between pointers and processor architecture
and what datatypes in FILE structure
Pointers are data types that store memory addresses. The size of those addresses is certainly defined by the processor architecture (some machines have 16-bit addresses, some 32, and some 64). As for the FILE structure...I'm really not understanding the question. Are you referring to the FILE * type that's returned from fopen()?
still some little bit confusion does those bits means the size of a pointer?
when i dereference the pointer with an int data type it give me 4 access block in decrementing mode like this:*(p-1),*(p-3) why?
sizeof(FILE*)=48;how those it read that such big data not on RAM but on hard disk..again thx a lot..i appreciate.
@@didoxgatete6338 I'm sorry. I don't understand your question.
@@didoxgatete6338 file struct does not contain the contents of the file. It probably just contains a pointer to a memory to which the file's content was loaded. Size of struct must be known, but when you read a file you don't know how big is that so the only way to "store" the content of a file in a struct is to give a pointer pointing to memory that has been read from the file. This is why FILE* is always some fixed size, not depending on file size.
@@geiger21 The FILE struct implementation is compiler dependent. More likely dependent on the implementation of the standard library which is dependent on the OS. There is a reason why there is gcc and MinGW (windows gcc port). The compiling process is almost the same, but the standard library isnt. One uses linuey system calls the other uses windows api. The standard library gives you standardized interface. But how it is working under the hood is more like blackbox and shouldnt be your concern. You can read the open source implementation of the std library if you really want to know. But its dependent on your OS.
hello sir,i presently i'm an electronic and electrical engineer and i am so passionate about programming however plc's ,logic controllers are queit a llittle not that.however i will love to know if learning c in 2019 could still be a relevant programming language for me and what is the possibility that it is multi fonctional in todays tech demand interms of software dev,mobile app dev etc thanks for your response
Short answer is, Yes, I think C is still a very relevant language. Long answer is partially contained here. th-cam.com/video/wcpH2PkC-94/w-d-xo.html
Pls make a video on how to embed python in c/c++ code
Just to clarify. You want to call python code from C/C++ or the other way around?
@@JacobSorber yeah I want to call python from c/c++ code
U r awesome
I thought it was impossible to overload a function based on return value only. . I suppose I was wrong
double getmean(const double *, int length);
void print_person_info(const person *);
Couldn’t it even be:
const double * const values
and
const person * const p
Because they’re pointers to values and neither the pointers or the values will be modified by the function?
But are you saying for pointers you don’t need a name? Or don’t need a name for the declaration but do for the definition?
I don’t think this was meant to be the focus of the video though
How about #pragma once? much simpler than defined :-)
Assumed that pragma once is not supported by all of the compilers and is not a part of C standard.
It's definitely a good option. #pragma once isn't part of the standard, but it's well-supported by a lot of compilers.
@@JacobSorber even then if you try to use more twice it'll produce the same error
I love how he chooses to zoom In rather than expand his terminal 😂
👍
Is that gnome builder?
No. It's either atom or vs code. Can't remember off the top of my head.
And it deserves to be mentioned: Putting code in a header file SHALL BE PUNISHED!!!
7:15 ah I C what you did there haha
😂
Programming music is quite similar to porno music, not that I know first hand. Thanks for sharing your expertise
#pragma once does the same?
Do you do Skype lessons? I could use some pointers lol.
Nice. :)
I don't. Too much to do, not enough time. But, if you have a specific request, I can look into making a future video on it.
@@JacobSorber have you done one on smart pointers?
Or threads? I am not sure if you stick to c or will do a c++11 video.
Also. It would be pretty cool if you have a mini assasignment at the end. Then post the code you wrote after a day or two. I always need some practice on the basics to make sure I am using them effectively
@@XenoTravis I have some threads videos. I'll add smart pointers to the list. I tend to focus on C because my operating systems class uses C, and I do a lot of C programming in my research. But, I'm definitely open to other languages.
@@JacobSorber sweet. C++ would make the most sense if you do another type of language. Before you do, it would be nice to have a video on the pros and cons of each.
Ever heard of pragma once?
name mangling. cool
Goldmine
#pragma once
Yes, that usually works, too. It's not required in the standards, but most compilers support it. Thanks.
I've come back just to say #PRAGMA ONCE
Don't use $(CPP) but $(CXX)
ayoo is that a KHMER DICTIONARY in the background
Just checked the source code for stdlib.h and it is indeed contained within "#ifndef _STDLIB_H" - and - " #endif /* stdlib.h */"
Thanks a lot!