Hello. I am trying to find new and exciting ways to optimize (read: shrink down) my current code and want to include an eeprom autorefresh option to cut down on variables. Basically, when I have the AutoRefreshCompile option set, I want it to create the variable "randomvariable". My code is pretty simple:
#define AutoRefreshCompile 1 #if(AutoRefreshCompile==1) { // line x extern signed short randomvariable; } // line y #endif
I am getting errors that read as follows:
VARS.H(x) error C141: syntax error near '{' VARS.H(y) error C141: syntax error near '}'
I'm guessing it is not possible to do this (if I remember correctly, variables have to be declared at the beginning and can't be in the middle of functions/code segments but maybe it's some really simple fix.
I realize this might not work but I figure it's worth a shot. Any suggestions? Thanks!
Please stop mixing C-preprocessor directives and normal C statements. This is not the first question of yours doing so. Get some books about using C and don't try to be 'more clever' than other C developers by writing obscure things.
And what, exactly, do you mean by that?
Remember that optimisation happens at compile time - you can't retrospectively optimise at run time!
"I'm guessing..."
Don't guess!!
If you want to out-smart the compiler, then you're going to need a really thorough understanding of not just the 'C' language, but also compiler technology.
Here are some 'C' references for you to study: blog.antronics.co.uk/.../12
I want it to create the variable "randomvariable"
And you are using extern for that? Either you are not telling the whole story, or you are very confused.
Or both.
Well, I guess you could use some sort of compression; but it seems rather unlikely that the overhead of the compression & decompression software would leave any net benefit - especially on an 8051.
Plus there'd be the speed penalty.
eg, http://www.keil.com/forum/21544/
going by the number and frequency of posts it look like work is light for a certain regular poster at the moment.
stop mixing C-preprocessor directives and normal C statements
if you can't figure out the difference, stop using it
So, did you stop to think whether a '{' or '}' are syntactically allowed at those respecpective places? What exactly did you think those would do?
optimize (read: shrink down) my current code and want to include an eeprom autorefresh option to cut down on variables
So how did you figure adding stuff whould shrink down your current code?
Every single previous post of mine has helped me immensely when it came down to leaving coding options in the code and enabling/disabling them using #define and #if statements. Maybe you guys see my previous posts as useless or poor uses but it has been a huge help for my project.
The reason I'm placing it in my VARS.H file is I don't need those variables declared at all if certain "preprocessor" conditions are met (in my case, AutoRefreshCompile==1). I've already used the #define statement to remove segments of code, I just have never used it to remove variables. The reason I ask is because of this post here, which just required removing a single bracket:
http://www.keil.com/forum/21544/
Now, I've read the preprocessor section at the link Andrew sent me and it does demonstrate what I was already doing. However, it does not say anything about my particular issue. I assume the problem I'm having is Keil specific and it's because I'm trying to insert code before all variables are declared (which I haven't had an issue with when using Atmel. Maybe Atmel's the exception but I do know Keil handles the order of variables/functions differently).
I used the extern declaration because that demonstrated the issue I was having. I also have it in my vars.c file:
#if(AutoRefreshCompile==1) { signed short randomvariable = 0; }
I usually don't show ALL my code because it's not necessary and would like to focus on the section I'm having an issue with. I guess I should note that I have variables declared above and below this (I guess I could move this to the end and maybe that would fix the issue). If you need more, let me know and I can give you more but I assumed this should be enough (maybe that's a bad assumption).
This is my issue (once again). You assume I haven't done the necessary homework and that I know nothing about C code and need a class. I've taken classes and maybe they haven't been as in depth as you would like but this particular case could have more to do with implementation of one particular section (in this case, preprocessors) or it could be Keil specific (though most issues I and others have are not Keil specific, so probably not). But I have done the reading, I did read the info you guys post here and, in this case, it didn't answer my question. Believe me when I say that coming to you guys is almost always a last resort, if only for the reason that some of you make asking even the most simple question a pain in the ass (and maybe that's the point).
And Hans, to answer your question, yes, I'm doing exactly that. By changing single bits, I can change how the code compiles based on the options I need. It's worked just fine in the past and I will continue to do this as it gives me additional code flexibility without adding any additional code space. If you want more information on what I'm doing, that's fine and I don't mind explaining.
Why the braces?
"I assume the problem I'm having is Keil specific"
Why? Have you tried the same code in another compiler?
Have you looked at the preprocessor output, as suggested, to see exactly what you're creating by this?
"You assume ... I know nothing about C code"
I don't think anyone's suggested that you know nothing, but it's clear that you lack some understanding - particularly regarding the preprocessor...
In the primary post the error message is:
The file name VARS.H implies it is a header file. Header files should not contain code, so your snippet:
is (I assume, because I can't know) not part of a function code but part of a declaration.
If this is true then of course the { and } are not allowed, simply write:
#define AutoRefreshCompile 1 #if(AutoRefreshCompile==1) extern signed short randomvariable; #endif
or something like that...
#define AutoRefreshCompile #ifdef AutoRefreshCompile extern signed short randomvariable; #endif
If this is not true, ignore my answer.
Hans, I ADDED preprocessor statements to REMOVE parts of code that are not always needed by setting a bit. Where did I lose you?
And as far as the previous suggestions go, you are 100% correct and brackets are not allowed in vars statements so it was a straight forward issue (and, as suggested, you are correct, I was lacking information). I now understand a bit better the limitations of what you can or cannot place in those files. I appreciate all the help! This should be the last little piece to further optimize. Thanks again for all your help!
That doesn't actually make sense.
I think you may still need to take some more time to too fully get to grips with the meaning of braces (aka "curly brackets"), and where they are allowed...?