Macros in C++
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- Опубліковано 16 гру 2017
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#define print(x) std::cout
Or with type safty, and proper compile time checking:
template
constexpr void print(Tostream ostrem = std::cout, Tlimit end='
' ,TStr ... to_print)
{
(std:: cout
#define begin {
#define end } ;
voilà ! pascal. And use just "end", voilà ! Ruby. :) cpp is really fun.
@@IamusTheFox you defined a template Tostream and never used it lmao
@@ShadowaOsu lmao, you're right, my bad.
@@IamusTheFox also it gives compile error for various of inputs when used in main, so I tried to give it a try as well
struct End {
const char* end;
constexpr End() : end("
") { }
constexpr End(const char* end) : end(end) { }
};
template
constexpr auto pyprint (const First& first, const Rest& ...rest) -> void {
if constexpr (sizeof... (rest) > 0) {
std::cout
#define true false
#define struct union
#define double float
#define break continue
#define ( )
#define ;
I think it would also be helpful to show common pitfalls of parameterized macros, such as the following 2 examples:
===================
#define MAX(x, y) x > y ? x : y
int main() { return MAX(7,5) * 10; }
Here main() will return 7 instead of 70:
7 > 5 ? 7 : 5 * 10 ==> 7
To fix this, do:
#define MAX(x, y) (x > y ? x : y)
===================
Another issue can be seen in this example:
#define MULT(x, y) (x * y)
int main() { return MULT(2+5, 10); }
Here main() will return 52 instead of 70:
2+5*10 ==> 52
To fix this, do:
#define MULT(x,y) ((x) * (y))
Of course, y can be a pointer so it is possible that *(y) is seen as a dereference. In addition, either x or y can be almost any text which can result in weird generated code.
===================
The takeaway is that parameterized macros are NOT functions: they simply replace symbols with parameterized text.
This can also result in the problem of massive code duplication, since a parameterized macro does not define a function in the program text segment, but is rather copied to every invocation.
The thought of seeing an “OPEN_CURLY” macro in real life cracked me up...at that point you know you’re dealing with a high-effort troll lmao
I once saw a
#define begin {
#define end }
And it was honestly a pretty wild experience. That simple change made C++ feel a hell of a lot like Ruby or Basic. Like:
void main() begin
if (1 > 0) begin
printf("whatever
");
end
end
Doesn't that look wild?
@@sebastiangudino9377 reminds me of Lua too
#define semicolan ;
My wife was like "what are you laughing so hard at?". I told her she wouldn't understand. She made me explain. She didn't understand.
Saw one image where he just defined some stuff and the code was like "frfr no cap" and he just replaces so many things with just random words and it looks like a sentence.
These have got to be the most concise and clear programming videos I've seen thus far.
Thanks for these videos man, I'm reading "Code Complete" and I thought I was getting to know C++ and C pretty well but everything he says about macros has gone over my head. This clears everything up, as so many of your videos do. The Static and Cost ones are my other favorites so far can't wait to see the rest this series is literally better than a college education.
You're an excellent educator. Great job! This was super helpful.
As some might have noticed the "blank" macro would actually not remove the entire LOG line in the code. It would leave the ";". This might cause people to want to include the ";" in the macro instead of writing it after the macro in the source code since that would not leave a line with just a ";". But a line with only ";" is totally acceptable and is just an empty statement which a decent compiler would most likley simply discard although there might exist some compilers that would actually insert NOOP instructions.
Point is, ";" by itself on a line is perfectly legal code.
Thanks for the clarification! Really appreciate it!
but you might want to be aware of this if it isn't by itself.
Its sometimes better to define the empty output as "{}" or "((void)0)" - These will make it a valid line of code without it doing anything. This is important if your macro can be called from within a single condition line, like if(x) MACRO();
called null statement
it is good to be aware of this but it doesn't matter if there is an extra colon ; after a statement
Bruh I love that I can expect a good ass cherno video on any cop topic I might want to learn. Really appreciate the work man 🙌🙌🙌
Really usefull compiler option : -E
It wills just process the precompiler routine and output your source code with all macro expanded.
For example : g++ -E main.cpp -o main.e
It's so comfy to watch it, I wish my lecturer was talking and makeing examples like you.
Thank for this series, helps a lot
Really loved the optimization of std::vector video. More videos on optimizing commonly libraries and functions would be super useful!
Or STL container comparisons and algorithms 🙂
good explained and helpful, thanks Cherno!
I use macros for Embedded microcontroller to configure my hardware easily.
your indications are very wise, thanks a lot !!
This video really helped me understand a lesson of learncpp, thanks a lot
Streams, Input and Output. As well as Files
Your example of logging bytes would be better served by creating a custom allocator that handled the metrics. Then you would override new to use your allocate/create functions. The bonus here is that you could add that allocator to a container and reap the same benefits.
Yes, but you still might want to track the file and line the allocation came from, which would require a macro.
The advice at 3:20 is golden bro!
Excellent C++ series. I am now a patreon.
Very good video and clear explanation
Other real life examples for macros would be to target different platforms. You write a conditional to decide between using Windows API or POSIX API. Or you want to do different stuff for an ARM build compared to x86. In open source projects macros are often used for optional features which might be enabled during configuration, like building ffmpeg with lots of optional third party libraries enabled. You can use macros to enable compiler specific stuff, like telling msvc right in the code to link against a library, but you want that part to be "excluded" for other compilers that don't understand or need this. Macros may also play a role when you build static libraries and DLLs for Windows, as the symbols in a header file need to be declared as either importing or exporting code or none of that.
Really like your C++ series.
Wondering if you could do some videos on MVS Windows GUI.
Not much out there on the Windows GUI, I know there are at least one error with MVS 17 in loading a Windows GUI setup. This is really tough for beginners.
Thanks,
Great series, these are presented really well. I don't understand why "#ifdef symbol" or "#ifndef symbol" is bad though. Header files have used this method to see if it has already been included for ages, windows header use it a lot and use it to set function names for Unicode or ascii. Would have been a good time to explain the underscore in symbol names. Still great simple video series worth watching.
This is te best explanation for this that I have seen on this flawed website known as UA-cam, thank you
Hi Cherno,
I know you will touch / have touched upon macros in more depth in your game engine / opengl series, but could you still make a separate video that's purely about macros (a part 2 of this one)? Because I don't follow your game engine / opengl series but I would still like to learn more about it from you.
Thanks ~
Nice explaination 👍🏻
You are an excellent teacher.
When we can expect the video in which you are going to show macros in more details and built in macro types , mentioned in this video?
Hey, great videos! Can you please make a video about the volatile keyword? :)
Another problem with the code is that LOG in release mode doesn't force a semicolon.
thank you
actually the
LOG(...);
in release mode would become
;
because the semicolon was not defined in the macro.
It no longer becomes simple copy paste when using any punctuation characters in the macro name. This code here for example, is not allowed:
#define print(x) std::cout
Awesome!
Let's make Python with #define 😂
I am learning SOOOO much more than what i did i uni!
Thank you for these incredible videos. I noticed in VS Code, some C++ I had installed offered a -- *lightbulb* | "inline macro?" | -- clickable tooltip that will let you graphically resolve whatever macro you are currently hovering over. Surely there are tools in actual Visual Studio to do that globally? Or stepwise for safety.
Macros are useful for writing parametrized test cases or "procedurally generated" code in general.
Clojure / Lisp take it to the next level with homoiconicity (code and data are the same thing)
In some cases, you may want to define your empty macro (the release version) as "{}" or "((void)0)", such as..
#define MACRO(x) ((void)0)
This will result in the macro generating a valid line of code that doesn't actually do anything. This would be important, if for example, you wanted to use it in places such as..
if( xyz )
MACRO(x);
I usually define a special "#define EMPTY_STATEMENT ((void)0)" somewhere near the top of my code to be used in these cases. It makes the macros themselves a little more readable ( #define MACRO(x) EMPTY_STATEMENT )
Thanks
You would have made an excellent Unreal Engine C++ trainer. Please do consider making a course on UE C++
Elegancko
if Anyone is watching this in 2020. If your Debug Code is not recognized after checking for PR_DEBUG you just need _DEBUG now. Hope this helps.
video idea for anyone just for fun: Making c++ looks like another programming language, using only MACROS!
yay!
Awesome.
With the knowledge we have now, does anyone have any recommendations for medium sized C++ projects? Maybe making use of OpenCV?
Would using the # define WAIT std::cin.get() still be bad for debugging purposes? If I am not using vim or some text editor that doesn't have break points, that looks like a pretty quick way to use my own sort of break point, especially if I am going to delete it after I am done writing the code anyway.
ILOVETHIS
Another reason why it might not be the best -- although IMO it's silly -- is that someone might tack a
very good. can you train qt. so we can make mobile application without lost of change of our code. Qt has opengl, opengl-es(angle) and vulkan implementations
Many a video about APIs I here about them all the time. I wood like to know: Wot they are and how they works?
what an intelligent human being.
Wouldn't it be usually better to use inline functions instead? They are safer and the performance difference is negligible. I know function calls use more cpu cycles but from my understanding inline functions are very optimized. I remember this from Effective C++ book
Wouldn't
#define LOG(x)
leave an extra semicolon in the code as it is not part of the definition?
yes it would in his example, but just a semicolon without any statements doesn't do anything
Java: *public static void main* is untouchable if you want your code to compile.
c++: hold my *MAIN_MARCO CHAR_EXCLAMATION*
Function pointers needed
why is this so funny to me. I need to grow up and get my big boy coder pants.
Good tutorial but if you use #define LOG(x), without anything, it compiles and works fine but the error code i get is weird? not 0 or 1.
is there a way to refer an array element by a name ? ex: #define a1 a[1]; a1=1; ?
Both Programming and English can be learned by watching your videos
@3:02
Damn,
That was useful
Because I don't like to type
"std::cout
Often I just use printf.
Hey Cherno, thanks for your wonderful lectures they're really awesome and they helped me a lot! But the only tiny problem is in your lessons when you going through the lessons you speak and explain so fast lol so I'm asking if you just could be a bit slower for sharing knowledge about c++ I'll be grateful
Thanks for everything ~ 😁
Reduce the playback speed to 0.75x.
For people having issues for ifdef DEBUG not showing correctly.
Use #Ifdef _DEBUG
I think the visual studio 2019 changed something for the debug :)
Define macros are easy, the difficult is to read, most of the time you don't know where they are and what they do. Some code depend of some macros to be defined and the docs sometimes don't put so much effort in explain it, and that's really confusing.
3:33 OOP programmers: nah im gonna make everything OOP
cool
Wow
#DontstopOPENGLseries , lot of things are still to be covered in there !!!
/* use this at your own risk */
#define true false
#define int
#define if while
#define else
we do a large amount of trolling
Where should I move on after finishing these series?
Does usage of macros effect performance or increase time in compilation since it needs to replace texts, like specially if the program has large number of macros?
If you have a large number of macros, you should probably reconsider your code.
@@angelcaru or your programming career
OMG thank you.This is exactly what i was looking for. OPEN_CURLY it is. No.. WAIT
Please don't pull another "Cherno" on us. Like you hype us with your quality content and then suddenly dissapear for half a year... :(
this is cool and all, but wouldn't this require wrapping a good portion of code with "LOG(x)" or are you just using Macros for short code to become shorter? Excuse me for being dumb here, but could you give me another example where you could use Macros to do "stuff" as it is currently shown to put shorter code instead of typing the larger amount. I do find it interesting where you showed in "Release Mode" some code can be used or not used.
The Cherno: C++
Subtitles/CC: *zip ocelots*
Slack in Unreal Engine uses macroses extensively and code becomes so cryptic...
@Cherno What Should I start first, 'Game Engine' playlist or 'OpenGL' ?
I haven't seen either, but I guess it would make more sense to start with OpenGL
Typedefs?
You are really great. I started learning cpp in 2013 but quit learning only because of curly brackets and over use of symbols like "
This joke has probably been cracked over 100000 times since Kernighan & Ritchie presented C in 1971.
*missed a lot of episodes* time to bing 😂
*Calculates minutes in all episodes combined* 10 HOURS?
Can I set debug mode in Linux using vscode?
I have a question. Can we redefine a preprocessor directive? For instance (#define ADD_LIB #include)
it doesn't work for normall defines
as for macros it doesn't work because # has a special meaning in macros
Why can't you put template functions in.cpp files
3:50 you're welcome
On that first code you wrote, there wasn't a "return 0;"
so when do I use the Return 0;
@Peterolen You can even go crazy and have `void main();` Not that you should, ever. Seriously, don't.
I don't like that he keeps omitting the return statement in main. I guess msvc silently optimizes it to return 0 or something like that. GCC will usually warn you and using "void main()" might not even be possible.
Do you do any consulting?
What IDE are you using or do you recommend for C/C++ development on linux?
@Artem Katerynych
Clion is available in linux
I don't use ide I use visual studio code with c++ extension and cmake extensions
How is that different from inlined functions?
Macros have nothing to do with functions, they're just text that is replaced. You could use them like a function, however you can do so much more with them. We'll explore this in later episodes.
Functions will get inlined if you use the appropriate keyword (eg. __force_inline for MSVC).
@TheChernoProject The code it will create tends to be the same though.
The fact that an "inline" function is inlined is decided by compiler, macros do not care about type safety or code syntax as they are parsed at preprocessing phase and are simple "find/replace" expressions. The most fun is to debug a macro because if for an inline function debugger will jump into function in case of a macro there is no code to jump to as the name of the macro was already replaced with specific text.
Well, yes, but macros are really useful where such text replacement is needed.
They should have used an assignment operator. People would understand instantly.
So you can create lua with macros, end is }, and so on
This video was quite helpful.
Could you please make a similar video but using VSCode? Thank you in advance!
2:24 Double negative : "nothing you can't not replace" = "nothing you can replace"
Now I realize Properties >> C/C++ >> Preprocess Def is macro.
I remember when I used static/dynamic library, I into Properties >> Linker blah blah ... hahahahahah Now I confident to use macro #pragma comment(lib, "nameLib.lib")
Nordic nRF SDK for their microcontrollers is completely written in macros (C not C++). It's a nightmare.
I've once seen a tiny single header file PNG decoder which was written almost entirely using macros. It was... interesting.
Why does he build for x86 and win32?
Google WOW64 or watch all TheCherno clips. Imagine a customer who still wants to run your application on 32 bit windows. Imagine the effort to maintain two versions of your application. You understand?
i like the video but hate the grandma couch
Never mind, apparently I broke my ten beer limit, so this one is on me.