I currently use some old C library for getting program options and would like to replace that with some proper C++ (mainly to become independent of that library, which is a real burden). I was looking into using boost.program_options, but am not sure it can support all I want. Some things I want is:
allow the following command-line syntax: myprogram option=value (in particular, I don't really want the --option value syntax)
use a default value if no value is provided (obviously this can be done in my program, but support in the options library would be nice)
allow default options (which are always present even if I don't give them) and an automatic help output consisting of all the options and their descriptions
allow mathematical parsing, i.e. (command line) myprogram option1=Pi option2=3/5 option3=sqrt(2) to give 3.1415..., 0.6, and 1.415... in my program
allow single values to be expanded. Let option_3Dpoint correspond to an std::array<double,3>, I want both myprogram option_3Dpoint=0,0,0 and myprogram option_3Dpoint=0 (expanding to 0,0,0) to work
Which of these can be supported by boost.program_options? Are there any alternatives?
boost.program_options is very good library. You can use to parse config files aswell. Answers:
Dont know but seems no builtin support.
Yes.
Yes.
No unless you make your own expression evaluation handler or use some other boost libs to do this.
Yes, you will need to write your own handler which creates 3DPoint object from string like 0,0,0
Related
I'm working on a code base that uses quite a bit of conditional compilation via macros passed as arguments to the compiler (i.e. gcc -DMACRO_HERE file.cpp). I would like to have a way to get a list of all the macros defined this way within the code so that I can write out all the used macros to the console and save files when the application is run, that way we know exactly what build was used.
I also need to do the same thing with the git hash but I think I can do that easily with a macro.
Edit 1: Note that this is not the same question as GCC dump preprocessor defines since I want the list available within the program and I only want the macros that are declared by being passed to the compiler with the -D argument
Edit 2: I also need it be cross compiler compatible since we use GCC, XL, CCE, CLANG, NVCC, HIP, and the MPI versions of those. Note that we're building with Make
Here's an outline of a possible solution.
The request is not well-specified because there is no guarantee that all object files will be built with the same conditional macros. So let's say that you want to capture the conditional macros specified for some designated source file.
On that basis, we can play a build trick, easy to do with make: the build recipe for that designated source file actually invokes a script, by inserting the path to the script at the beginning of the compile line.
The script runs through its arguments, selects the ones which start -D, and uses them to create a simple C source file which defines an array const char* build_options[], populating it with stringified versions of the command line arguments. (Unless you're a perfectionist, you don't need to do heroics to correctly escape the strings, because no sane build configuration would use -D arguments which require heroic escaping.)
Once the source file is built, the script saves it and either uses the command-line it was passed as its arguments to compile it, or leaves it to be compiled by some later build step.
I am currently writing a program that sits on top of a C++ interpreter. The user inputs C++ commands at runtime, which are then passed into the interpreter. For certain patterns, I want to replace the command given with a modified form, so that I can provide additional functionality.
I want to replace anything of the form
A->Draw(B1, B2)
with
MyFunc(A, B1, B2).
My first thought was regular expressions, but that would be rather error-prone, as any of A, B1, or B2 could be arbitrary C++ expressions. As these expressions could themselves contain quoted strings or parentheses, it would be quite difficult to match all cases with a regular expression. In addition, there may be multiple, nested forms of this expression
My next thought was to call clang as a subprocess, use "-dump-ast" to get the abstract syntax tree, modify that, then rebuild it into a command to be passed to the C++ interpreter. However, this would require keeping track of any environment changes, such as include files and forward declarations, in order to give clang enough information to parse the expression. As the interpreter does not expose this information, this seems infeasible as well.
The third thought was to use the C++ interpreter's own internal parsing to convert to an abstract syntax tree, then build from there. However, this interpreter does not expose the ast in any way that I was able to find.
Are there any suggestions as to how to proceed, either along one of the stated routes, or along a different route entirely?
What you want is a Program Transformation System.
These are tools that generally let you express changes to source code, written in source level patterns that essentially say:
if you see *this*, replace it by *that*
but operating on Abstract Syntax Trees so the matching and replacement process is
far more trustworthy than what you get with string hacking.
Such tools have to have parsers for the source language of interest.
The source language being C++ makes this fairly difficult.
Clang sort of qualifies; after all it can parse C++. OP objects
it cannot do so without all the environment context. To the extent
that OP is typing (well-formed) program fragments (statements, etc,.)
into the interpreter, Clang may [I don't have much experience with it
myself] have trouble getting focused on what the fragment is (statement? expression? declaration? ...). Finally, Clang isn't really a PTS; its tree modification procedures are not source-to-source transforms. That matters for convenience but might not stop OP from using it; surface syntax rewrite rule are convenient but you can always substitute procedural tree hacking with more effort. When there are more than a few rules, this starts to matter a lot.
GCC with Melt sort of qualifies in the same way that Clang does.
I'm under the impression that Melt makes GCC at best a bit less
intolerable for this kind of work. YMMV.
Our DMS Software Reengineering Toolkit with its full C++14 [EDIT July 2018: C++17] front end absolutely qualifies. DMS has been used to carry out massive transformations
on large scale C++ code bases.
DMS can parse arbitrary (well-formed) fragments of C++ without being told in advance what the syntax category is, and return an AST of the proper grammar nonterminal type, using its pattern-parsing machinery. [You may end up with multiple parses, e.g. ambiguities, that you'll have decide how to resolve, see Why can't C++ be parsed with a LR(1) parser? for more discussion] It can do this without resorting to "the environment" if you are willing to live without macro expansion while parsing, and insist the preprocessor directives (they get parsed too) are nicely structured with respect to the code fragment (#if foo{#endif not allowed) but that's unlikely a real problem for interactively entered code fragments.
DMS then offers a complete procedural AST library for manipulating the parsed trees (search, inspect, modify, build, replace) and can then regenerate surface source code from the modified tree, giving OP text
to feed to the interpreter.
Where it shines in this case is OP can likely write most of his modifications directly as source-to-source syntax rules. For his
example, he can provide DMS with a rewrite rule (untested but pretty close to right):
rule replace_Draw(A:primary,B1:expression,B2:expression):
primary->primary
"\A->Draw(\B1, \B2)" -- pattern
rewrites to
"MyFunc(\A, \B1, \B2)"; -- replacement
and DMS will take any parsed AST containing the left hand side "...Draw..." pattern and replace that subtree with the right hand side, after substituting the matches for A, B1 and B2. The quote marks are metaquotes and are used to distinguish C++ text from rule-syntax text; the backslash is a metaescape used inside metaquotes to name metavariables. For more details of what you can say in the rule syntax, see DMS Rewrite Rules.
If OP provides a set of such rules, DMS can be asked to apply the entire set.
So I think this would work just fine for OP. It is a rather heavyweight mechanism to "add" to the package he wants to provide to a 3rd party; DMS and its C++ front end are hardly "small" programs. But then modern machines have lots of resources so I think its a question of how badly does OP need to do this.
Try modify the headers to supress the method, then compiling you'll find the errors and will be able to replace all core.
As far as you have a C++ interpreter (as CERN's Root) I guess you must use the compiler to intercept all the Draw, an easy and clean way to do that is declare in the headers the Draw method as private, using some defines
class ItemWithDrawMehtod
{
....
public:
#ifdef CATCHTHEMETHOD
private:
#endif
void Draw(A,B);
#ifdef CATCHTHEMETHOD
public:
#endif
....
};
Then compile as:
gcc -DCATCHTHEMETHOD=1 yourfilein.cpp
In case, user want to input complex algorithms to the application, what I suggest is to integrate a scripting language to the app. So that the user can write code [function/algorithm in defined way] so the app can execute it in the interpreter and get the final results. Ex: Python, Perl, JS, etc.
Since you need C++ in the interpreter http://chaiscript.com/ would be a suggestion.
What happens when someone gets ahold of the Draw member function (auto draw = &A::Draw;) and then starts using draw? Presumably you'd want the same improved Draw-functionality to be called in this case too. Thus I think we can conclude that what you really want is to replace the Draw member function with a function of your own.
Since it seems you are not in a position to modify the class containing Draw directly, a solution could be to derive your own class from A and override Draw in there. Then your problem reduces to having your users use your new improved class.
You may again consider the problem of automatically translating uses of class A to your new derived class, but this still seems pretty difficult without the help of a full C++ implementation. Perhaps there is a way to hide the old definition of A and present your replacement under that name instead, via clever use of header files, but I cannot determine whether that's the case from what you've told us.
Another possibility might be to use some dynamic linker hackery using LD_PRELOAD to replace the function Draw that gets called at runtime.
There may be a way to accomplish this mostly with regular expressions.
Since anything that appears after Draw( is already formatted correctly as parameters, you don't need to fully parse them for the purpose you have outlined.
Fundamentally, the part that matters is the "SYMBOL->Draw("
SYMBOL could be any expression that resolves to an object that overloads -> or to a pointer of a type that implements Draw(...). If you reduce this to two cases, you can short-cut the parsing.
For the first case, a simple regular expression that searches for any valid C++ symbol, something similar to "[A-Za-z_][A-Za-z0-9_\.]", along with the literal expression "->Draw(". This will give you the portion that must be rewritten, since the code following this part is already formatted as valid C++ parameters.
The second case is for complex expressions that return an overloaded object or pointer. This requires a bit more effort, but a short parsing routine to walk backward through just a complex expression can be written surprisingly easily, since you don't have to support blocks (blocks in C++ cannot return objects, since lambda definitions do not call the lambda themselves, and actual nested code blocks {...} can't return anything directly inline that would apply here). Note that if the expression doesn't end in ) then it has to be a valid symbol in this context, so if you find a ) just match nested ) with ( and extract the symbol preceding the nested SYMBOL(...(...)...)->Draw() pattern. This may be possible with regular expressions, but should be fairly easy in normal code as well.
As soon as you have the symbol or expression, the replacement is trivial, going from
SYMBOL->Draw(...
to
YourFunction(SYMBOL, ...
without having to deal with the additional parameters to Draw().
As an added benefit, chained function calls are parsed for free with this model, since you can recursively iterate over the code such as
A->Draw(B...)->Draw(C...)
The first iteration identifies the first A->Draw( and rewrites the whole statement as
YourFunction(A, B...)->Draw(C...)
which then identifies the second ->Draw with an expression "YourFunction(A, ...)->" preceding it, and rewrites it as
YourFunction(YourFunction(A, B...), C...)
where B... and C... are well-formed C++ parameters, including nested calls.
Without knowing the C++ version that your interpreter supports, or the kind of code you will be rewriting, I really can't provide any sample code that is likely to be worthwhile.
One way is to load user code as a DLL, (something like plugins,)
this way, you don't need to compile your actual application, just the user code will be compiled, and you application will load it dynamically.
I'm using a tool chain that is more like a web. There are lotys of alternate start points, all resulting in a single final output.
I typically use make or scons - actually, I prefer scons, but my team highly prefers make. I'm open to other build tools.
E.g. final_result depends on penultimate
final_result: penultimate
penultimate may be made in any of several different ways:
If starting from file1, then
penultimate: file1 ; rule1
If starting from file2, then
penultimate: file2 ; rule2
Q: how do I specify to start with file2, not file1?
I suppose that I could use a command line switch and ifdeffing. But I would prefer to have make or scons figure out "Hey, there's a file2 around, so I should use rule2, not fil1/rule1". In part because the web is much more complex than this...
Worse, sometimes an intermediate on one path may be a start on another. Let's see:
A .s produces a .diag
foo.diag: foo.s
But sometimes there is no .s, and I just have a .diag that somebody else gave me already built.
A .diag produces a .heximg, and a .hwresult
foo.hwresult: hwsim foo.heximg
foo.heximg: foo.diag
But sometimes I am given a .img directly
Etc.
I just want to write the overall dependency graph, and say "OK, now here's what I have been given - now how do you get to the final result?"
With what I have now, when I am given, say, a foo.img, I get told (by make in this case) "foo.s not dfound". Because make wants to go all the way back in the dependency graph to tell if foo.img is out of date, whereas I want to say "assume foo.img is up to date, and work forwrads for stuff that depends on foo.img, instead of going back for stuff that foo.img depends on."
You have to do it all with pattern rules (implicit rules). If you specify an explicit rule then make considers that a hard dependency and if some portion of the dependency is not met, make will fail.
If you use an implicit rule then make will consider that a POSSIBLE way to build the target. If that way doesn't work (because some prerequisite does not exist and make doesn't know how to build it) make will try another way. If no way works, and the target already exists, make will just use that target without having to update it.
Also you say "a .diag produces a .heximg and a .hwresult" then gave a strange example makefile syntax that I didn't recognize, but FYI with pattern rules you can specify that a single command generates multiple outputs (you can't do this with explicit rules):
%.heximg %.hwresult: %.diag
Here's the bad news: the only way to define an implicit rule in GNU make is if there is a common "stem" in the filename. That is, you can write an implicit rule that converts foo.diag to foo.heximg by writing a pattern rule "%.heximg: %.diag", because they have a common stem "foo", but there's no way to create a pattern rule for a compilation from "foo1" to "penultimate", because they don't share a common stem.
I'm not sure, but probably you're looking for Double-Colon Rules:
Double-colon rules are explicit rules written with :: instead of : after the target names. They are handled differently from ordinary rules when the same target appears in more than one rule.
Double-colon rules are somewhat obscure and not often very useful; they provide a mechanism for cases in which the method used to update a target differs depending on which prerequisite files caused the update, and such cases are rare.
While using compiler such g++ on command line, there are some parameters, which need to be given in all invocation of g++, and which are different from default parameters. Is there a way (e.g. using bashrc), so that my selected parameters canbe made default. I am compiling single files, so using makefile is not convenient.
I could not find exact answer anywhere among previuos answers.
I guess you could put something like this in your .bashrc file:
alias g++='g++ -WHATEVER'
I'm personally not a big fan of this, because it could get confusing. I would rather do something like this:
alias my_g++='g++ -WHATEVER'
It should turn this
int Yada (int yada)
{
return yada;
}
into this
int Yada (int yada)
{
SOME_HEIDEGGER_QUOTE;
return yada;
}
but for all (or at least a big bunch of) syntactically legal C/C++ - function and method constructs.
Maybe you've heard of some Perl library that will allow me to perform these kinds of operations in a view lines of code.
My goal is to add a tracer to an old, but big C++ project in order to be able to debug it without a debugger.
Try Aspect C++ (www.aspectc.org). You can define an Aspect that will pick up every method execution.
In fact, the quickstart has pretty much exactly what you are after defined as an example:
http://www.aspectc.org/fileadmin/documentation/ac-quickref.pdf
If you build using GCC and the -pg flag, GCC will automatically issue a call to the mcount() function at the start of every function. In this function you can then inspect the return address to figure out where you were called from. This approach is used by the linux kernel function tracer (CONFIG_FUNCTION_TRACER). Note that this function should be written in assembler, and be careful to preserve all registers!
Also, note that this should be passed only in the build phase, not link, or GCC will add in the profiling libraries that normally implement mcount.
I would suggest using the gcc flag "-finstrument-functions". Basically, it automatically calls a specific function ("__cyg_profile_func_enter") upon entry to each function, and another function is called ("__cyg_profile_func_exit") upon exit of the function. Each function is passed a pointer to the function being entered/exited, and the function which called that one.
You can turn instrumenting off on a per-function or per-file basis... see the docs for details.
The feature goes back at least as far as version 3.0.4 (from February 2002).
This is intended to support profiling, but it does not appear to have side effects like -pg does (which compiles code suitable for profiling).
This could work quite well for your problem (tracing execution of a large program), but, unfortunately, it isn't as general purpose as it would have been if you could specify a macro. On the plus side, you don't need to worry about remembering to add your new code into the beginning of all new functions that are written.
There is no such tool that I am aware of. In order to recognise the correct insertion point, the tool would have to include a complete C++ parser - regular expressions are not enough to accomplish this.
But as there are a number of FOSS C++ parsers out there, such a tool could certainly be written - a sort of intelligent sed for C++ code. The biggest problem would probably be designing the specification language for the insert/update/delete operation - regexes are obviously not the answer, though they should certainly be included in the language somehow.
People are always asking here for ideas for projects - how about this for one?
I use this regex,
"(?<=[\\s:~])(\\w+)\\s*\\([\\w\\s,<>\\[\\].=&':/*]*?\\)\\s*(const)?\\s*{"
to locate the functions and add extra lines of code.
With that regex I also get the function name (group 1) and the arguments (group 2).
Note: you must filter out names like, "while", "do", "for", "switch".
This can be easily done with a program transformation system.
The DMS Software Reengineering Toolkit is a general purpose program transformation system, and can be used with many languages (C#, COBOL, Java, EcmaScript, Fortran, ..) as well as specifically with C++.
DMS parses source code (using full langauge front end, in this case for C++),
builds Abstract Syntax Trees, and allows you to apply source-to-source patterns to transform your code from one C# program into another with whatever properties you wish. THe transformation rule to accomplish exactly the task you specified would be:
domain CSharp.
insert_trace():function->function
"\visibility \returntype \fnname(int \parametername)
{ \body } "
->
"\visibility \returntype \fnname(int \parametername)
{ Heidigger(\CppString\(\methodname\),
\CppString\(\parametername\),
\parametername);
\body } "
The quote marks (") are not C++ quote marks; rather, they are "domain quotes", and indicate that the content inside the quote marks is C++ syntax (because we said, "domain CSharp"). The \foo notations are meta syntax.
This rule matches the AST representing the function, and rewrites that AST into the traced form. The resulting AST is then prettyprinted back into source form, which you can compile. You probably need other rules to handle other combinations of arguments; in fact, you'd probably generalize the argument processing to produce (where practical) a string value for each scalar argument.
It should be clear you can do a lot more than just logging with this, and a lot more than just aspect-oriented programming, since you can express arbitrary transformations and not just before-after actions.