I'm trying to remove a data source from a rrd db.
I found I can do something like
"rrdtool tune mydb.rrd DEL:source_name"
and it works, but I want to do it from C/C++ code.
I could use the system function in Linux, but I don't
like the overhead.
I looked in https://oss.oetiker.ch/rrdtool/doc/librrd.en.html
to see if there is something I could use, but I didn't find anything.
I also looked in the rrd source code from https://github.com/oetiker/rrdtool-1.x/tree/master/src
and I found they call rrd_modify_r2() to remove sources, but this function is static, so it's not exported (as opposed to rrdc_create_r2)
So, how can I remove a source from C/C++ code ?
thanks,
Catalin
You use of course rrdtool tune filename.rrd DEL:ds-name to do this from the commandline, as you note.
However the RRDTool C bindings in librrd are not as comprehensive, and do not appear to expose this functionality. Not sure why - the modify functions is clearly useful - but thats how it seems to be.
One option you have would be to simply call the external rrdtool binary with fork/exec, passing the appropriate commandline. This is not a particularly pretty way to do it, but is more portable and compatible with the published interface.
While writing a Haskell binding for some libs written in C, a thing has to do is writing docs in haddock format. But since normally the binding is just plain, the doc would be just reformat of original libs' doc.
So my question is, is there some tools to help with this? Thanks.
I don't know of any tool for that. Since C docs can take many forms, I don't think there is any tool.
If the binding is indeed plain, essentially everything in IO, same names as the C library, etc. there is a very lazy option: provide a link to the C docs and refer to that.
Better: if the C docs are online, and each function/variable/entity has its own link, provide a link for each entity. In such way, the Haskell programmer can find your docs in Hackage, as usual, and then it's just one more click away to the real docs.
Of course, ideally one should copy the C docs, so that it's immediately available. However, this can require a lot of work, and some care in handling copyright correctly.
I understand VC++ will let you emit C++ source files which are the result of preprocessor operations e.g. macros are expanded and includes "copy-pasted in line".
Is it possible to restrict this simply to embed included files, which are files in my own project rather than standard libraries?
From the outside there's no way you can tell from which syntax form (<> or "") the content is being preprocessed. Unless a kind of API was exposed by the preprocessor, which is not the case here.
A not so elegant (and not strictly correct) solution I could propose would be to index a preprocessed version of all Standard headers (there are not that many) and after preprocessing the source of interest you could run a string matching script to detect the known files and remove the corresponding content from the final output.
Notice this is subjected to flaws because the #include system is purely textual and influenced by whatever macros are (un)defined at the time of inclusion and order matters. But depending on the complexity of the code you're working on this might give reasonable results.
By the way, may I ask what is the ultimate goal of your task?
Edit: Or actually... Maybe it's possible that you filter the sources before-hand to remove the undesired #includes and then submit it to preprocessing?
I have been getting very frustrated recently in dealing with a massive bulk of legacy code which I am trying to get familiar with.
Say I try to search for a particular function call, I get loads of results that turn out to be completely irrelevant; some of them are easy to spot, eg a comment saying
// Fixed functionality in foo() so don't need to handle this here any more
But others are much harder to spot manually, because they turn out to be calls from other functions in modules that are only compiled in certain cases, or are part of a much larger block of code that is #if 0'd out in its entirety.
What I'd like would be a search tool that would allow me to search for a term and give me the choice to include or exclude commented out or #if 0'd out code. Then the search results would be displayed alongside a list of #defines that are required in order for that snippet of code to be relevant.
I'm working in C / C++, but other than the specific comment syntax I guess the techniques should be more generally applicable.
Does such a tool exist?
Not entirely what you're after, but I find this quite handy.
GrepWin - A free visual "grep" tool for searching files.
I find it quite helpful because:
Its a separate app (doesn't lock up my editor)
Handles Regular expressions
Its fast
Can specify what folder to search, and what filetypes (handles regex's here too)
Can limit by file size
Can include subdirs (or exclude by regex)
etc.
Almost any decent source browser will let you go to where a function is defined, and/or list all the calls of that function and take you directly to a call site. This will normally be based on a fairly complete parse of the source code so it will ignore comments, code that's excluded by the preprocessor, and so on (in fact, in at least one case, the parser used by the source browser is almost certainly better than the one used in the compiler itself).
I know that its possible to read from a .txt file and then convert various parts of that into string, char, and int values, but is it possible to take a string and use it as real code in the program?
Code:
string codeblock1="cout<<This is a test;";
string codeblock2="int array[5]={0,6,6,3,5};}";
int i;
cin>>i;
if(i)
{
execute(codeblock1);
}
else
{
execute(codeblock2);
}
Where execute is a function that converts from text to actual code (I don't know if there actually is a function called execute, I'm using it for the purpose of my example).
In C++ there's no simple way to do this. This feature is available in higher-level languages like Python, Lisp, Ruby and Perl (usually with some variation of an eval function). However, even in these languages this practice is frowned upon, because it can result in very unreadable code.
It's important you ask yourself (and perhaps tell us) why you want to do it?
Or do you only want to know if it's possible? If so, it is, though in a hairy way. You can write a C++ source file (generate whatever you want into it, as long as it's valid C++), then compile it and link to your code. All of this can be done automatically, of course, as long as a compiler is available to you in runtime (and you just execute it with system). I know someone who did this for some heavy optimization once. It's not pretty, but can be made to work.
You can create a function and parse whatever strings you like and create a data structure from it. This is known as a parse tree. Subsequently you can examine your parse tree and generate the necessary dynamic structures to perform the logic therin. The parse tree is subsequently converted into a runtime representation that is executed.
All compilers do exactly this. They take your code and they produce machine code based on this. In your particular case you want a language to write code for itself. Normally this is done in the context of a code generator and it is part of a larger build process. If you write a program to parse your language (consider flex and bison for this operation) that generates code you can achieve the results you desire.
Many scripting languages offer this sort of feature, going all the way back to eval in LISP - but C and C++ don't expose the compiler at runtime.
There's nothing in the spec that stops you from creating and executing some arbitrary machine language, like so:
char code[] = { 0x2f, 0x3c, 0x17, 0x43 }; // some machine code of some sort
typedef void (FuncType*)(); // define a function pointer type
FuncType func = (FuncType)code; // take the address of the code
func(); // and jump to it!
but most environments will crash if you try this, for security reasons. (Many viruses work by convincing ordinary programs to do something like this.)
In a normal environment, one thing you could do is create a complete program as text, then invoke the compiler to compile it and invoke the resulting executable.
If you want to run code in your own memory space, you could invoke the compiler to build you a DLL (or .so, depending on your platform) and then link in the DLL and jump into it.
First, I wanted to say, that I never implemented something like that myself and I may be way off, however, did you try CodeDomProvider class in System.CodeDom.Compiler namespace? I have a feeling the classes in System.CodeDom can provide you with the functionality you are looking for.
Of course, it will all be .NET code, not any other platform
Go here for sample
Yes, you just have to build a compiler (and possibly a linker) and you're there.
Several languages such as Python can be embedded into C/C++ so that may be an option.
It's kind of sort of possible, but not with just straight C/C++. You'll need some layer underneath such as LLVM.
Check out c-repl and ccons
One way that you could do this is with Boost Python. You wouldn't be using C++ at that point, but it's a good way of allowing the user to use a scripting language to interact with the existing program. I know it's not exactly what you want, but perhaps it might help.
Sounds like you're trying to create "C++Script", which doesn't exist as far as I know. C++ is a compiled language. This means it always must be compiled to native bytecode before being executed. You could wrap the code as a function, run it through a compiler, then execute the resulting DLL dynamically, but you're not going to get access to anything a compiled DLL wouldn't normally get.
You'd be better off trying to do this in Java, JavaScript, VBScript, or .NET, which are at one stage or another interpreted languages. Most of these languages either have an eval or execute function for just that, or can just be included as text.
Of course executing blocks of code isn't the safest idea - it will leave you vulnerable to all kinds of data execution attacks.
My recommendation would be to create a scripting language that serves the purposes of your application. This would give the user a limited set of instructions for security reasons, and allow you to interact with the existing program much more dynamically than a compiled external block.
Not easily, because C++ is a compiled language. Several people have pointed round-about ways to make it work - either execute the compiler, or incorporate a compiler or interpreter into your program. If you want to go the interpreter route, you can save yourself a lot of work by using an existing open source project, such as Lua