Assume I have a libconfig::config object, can i readFile for several times like this:
libconfig::Config cfg;
cfg.readFiles("./a.cfg");
cfg.readFiles("./b.cfg");
and what will happen if a.cfg and b.cfg have same key?
If this doesnt work, is there any methods can let me merge two config files' setting into one object?
At first, it seems that method is readFile() not readFiles() unless I'm checking incorrect library.
Second, everytime readFile() is called, values in config will be reset. So after cfg.readFiles("./b.cfg"); you will not have a.cfg configuration anymore.
Related
I am facing the following issue: In our project, we have a main class with a main method called "run". This method calls hundreds of other functions, classes etc.
We are now calling this run method in a test in a for loop multiple times, something like that:
for(float test_time = 0; test_time < 10.0; test_time += 0.005){
outputStruct = mainClass.run(inputStruct);
}
I now want to save all local variables of all functions and methods and all member variables of all included objects that are seen when this for loop is executed. And I want to have a snapshot of this for each loop iteration. So in this example, there should be like 2000 snapshots of all my variables.
Is this somehow possible? I see that GDB has some "trace" functionality, but it's not clear for me how I can tell GDB that it should save everything that was "seen" while executing the mainClass.run method. It should "only" remember the last state of each member and local variable. And when test_time increments, it can finalize the current snapshot and create a new one for the next time slot.
Is something like this possible? Since our usecase is some physics based scenario, it is every interesting to see how certain values change over time in a plot later. I don't mind what the format of the output file of GDB is, it will be parsed later anyway, as long as the information is somehow inside. Of course, the cleaner the file looks the better :).
Thank you for your support guys!
It seems trivial, but I've searched far and wide.
I'm using this resource to make v8 run with ES Modules and I'm trying to implement my own search/load algorithm. Thus far, I've managed to make a simple system which loads a file from a known location, however I'd like to implement external modules. This means that the known location is actually unknown throughout the application. Take the following directory tree as an example:
~/
- index.js
import 'module1_index'; // This is successfully resolved to /libs/module1/module1_index.js
/libs/module1/
- module1_index.js
export * from './lib.js' // This import fails because it is looking for ./lib.js in ~/source
- lib.js
export /* literally anything */
The above example begins by executing the index.js file from ~. When module1_index.js is executed, lib.js is looked for from ~ and consequently fails. In order to address this, the files must be looked for relative to the file being executed at the moment, however I have not found a means to do this.
First Attempt
I'm given the opportunity to look for the file in the callResolve method (main.cpp:280):
v8::MaybeLocal<v8::Module> callResolve(v8::Local<v8::Context> context, v8::Local<v8::String> specifier, v8::Local<v8::Module> referrer)
or in loadModule (main.cpp:197)
v8::MaybeLocal<v8::Module> loadModule(char code[], char name[], v8::Local<v8::Context> cx)
however, as mentioned, I have found no function by which to extract the ScriptOrigin from the module. I should mention, when files are successfully resolved, the ScriptOrigin is initiated with the exact path to the file, and is reliable.
Second Attempt
I set up a stack, which keeps track of the current file being executed. Every import which is made is pushed onto the stack. Once the file has finished executing, it is popped. This also did not work, as there was no way to reliably determine once the file had finished executing.
It seems that the loadModule function does just that: loads. It does not execute, so I cannot pop after the module has loaded, as the imports are not fully resolved. The checkModule/execModule functions are only invoked on dynamic imports, making them useless to determining the completion of a static import.
I'm at a loss. I'm not familiar with v8 enough to know where to look, although I have dug through some NodeJS source code looking for an implementation, to no avail.
Any pointers are greatly appreciated.
Thanks.
Jake.
I don't know much about module resolution, but looking at V8's sources, I can see an example mapping a v8::Module to a std::string absolute_path, which sounds like what you're looking for. I'm not copying the whole code here, because the way it uses custom metadata is a bit involved; the short story is that it keeps a std::unordered_map to keep data about each module's source on the side. (I wonder if it would be possible to use Module::ScriptId() as that map's key, for simplification.)
Code search finds a bunch more example uses of InstantiateModule, mostly in tests. Tests often serve as useful examples/documentation :-)
Let me elaborate on the title:
I want to implement a system that would allow me to enable/disable/modify the general behavior of my program. Here are some examples:
I could switch off and on logging
I could change if my graphing program should use floating or pixel coordinates
I could change if my calculations should be based upon some method or some other method
I could enable/disable certain aspects like maybe a extension api
I could enable/disable some basic integrated profiler (if I had one)
These are some made-up examples.
Now I want to know what the most common solution for this sort of thing is.
I could imagine this working with some sort of singelton class that gets instanced globally or in some other globally available object. Another thing that would be possible would be just constexpr or other variables floating around in a namespace, again globally.
However doing something like that, globally, feels like bad practise.
second part of the question
This might sound like I cant decide what I want, but I want a way to modify all these switches/flags or whatever they are actually called in a single location, without tying any of my classes to it. I don't know if this is possible however.
Why don't I want to do that? Well I like to make my classes somewhat reusable and I don't like tying classes together, unless its required by the DRY principle and or inheritance. I basically couldn't get rid of the flags without modifying the possible hundreds of classes that used them.
What I have tried in the past
Having it all as compiler defines. This worked reasonably well, however I didnt like that I couldnt make it so if the flag file was gone there were some sort of default settings that would make the classes themselves still operational and changeable (through these default values)
Having it as a class and instancing it globally (system class). Worked ok, however I didnt like instancing anything globally. Also same problem as above
Instancing the system class locally and passing it to the classes on construction. This was kinda cool, since I could make multiple instruction sets. However at the same time that kinda ruined the point since it would lead to things that needed to have one flag set the same to have them set differently and therefore failing to properly work together. Also passing it on every construction was a pain.
A static class. This one worked ok for the longest time, however there is still the problem when there are missing dependencies.
Summary
Basically I am looking for a way to have a single "place" where I can mess with some values (bools, floats etc.) and that will change the behaviour of all classes using them for whatever, where said values either overwrite default values or get replaced by default values if said "place" isnt defined.
If a Singleton class does not work for you , maybe using a DI container may fit in your third approach? It may help with the construction and make the code more testable.
There are some DI frameworks for c++, like https://github.com/google/fruit/wiki or https://github.com/boost-experimental/di which you can use.
If you decide to use switch/flags, pay attention for "cyclometric complexity".
If you do not change the skeleton of your algorithm but only his behaviour according to the objets in parameter, have a look at "template design pattern". This method allow you to define a generic algorithm and specify particular step for a particular situation.
Here's an approach I found useful; I don't know if it's what you're looking for, but maybe it will give you some ideas.
First, I created a BehaviorFlags.h file that declares the following function:
// Returns true iff the given feature/behavior flag was specified for us to use
bool IsBehaviorFlagEnabled(const char * flagName);
The idea being that any code in any of your classes could call this function to find out if a particular behavior should be enabled or not. For example, you might put this code at the top of your ExtensionsAPI.cpp file:
#include "BehaviorFlags.h"
static const enableExtensionAPI = IsBehaviorFlagEnabled("enable_extensions_api");
[...]
void DoTheExtensionsAPIStuff()
{
if (enableExtensionsAPI == false) return;
[... otherwise do the extensions API stuff ...]
}
Note that the IsBehaviorFlagEnabled() call is only executed once at program startup, for best run-time efficiency; but you also have the option of calling IsBehaviorFlagEnabled() on every call to DoTheExtensionsAPIStuff(), if run-time efficiency is less important that being able to change your program's behavior without having to restart your program.
As far as how the IsBehaviorFlagEnabled() function itself is implemented, it looks something like this (simplified version for demonstration purposes):
bool IsBehaviorFlagEnabled(const char * fileName)
{
// Note: a real implementation would find the user's home directory
// using the proper API and not just rely on ~ to expand to the home-dir path
std::string filePath = "~/MyProgram_Settings/";
filePath += fileName;
FILE * fpIn = fopen(filePath.c_str(), "r"); // i.e. does the file exist?
bool ret = (fpIn != NULL);
fclose(fpIn);
return ret;
}
The idea being that if you want to change your program's behavior, you can do so by creating a file (or folder) in the ~/MyProgram_Settings directory with the appropriate name. E.g. if you want to enable your Extensions API, you could just do a
touch ~/MyProgram_Settings/enable_extensions_api
... and then re-start your program, and now IsBehaviorFlagEnabled("enable_extensions_api") returns true and so your Extensions API is enabled.
The benefits I see of doing it this way (as opposed to parsing a .ini file at startup or something like that) are:
There's no need to modify any "central header file" or "registry file" every time you add a new behavior-flag.
You don't have to put a ParseINIFile() function at the top of main() in order for your flags-functionality to work correctly.
You don't have to use a text editor or memorize a .ini syntax to change the program's behavior
In a pinch (e.g. no shell access) you can create/remove settings simply using the "New Folder" and "Delete" functionality of the desktop's window manager.
The settings are persistent across runs of the program (i.e. no need to specify the same command line arguments every time)
The settings are persistent across reboots of the computer
The flags can be easily modified by a script (via e.g. touch ~/MyProgram_Settings/blah or rm -f ~/MyProgram_Settings/blah) -- much easier than getting a shell script to correctly modify a .ini file
If you have code in multiple different .cpp files that needs to be controlled by the same flag-file, you can just call IsBehaviorFlagEnabled("that_file") from each of them; no need to have every call site refer to the same global boolean variable if you don't want them to.
Extra credit: If you're using a bug-tracker and therefore have bug/feature ticket numbers assigned to various issues, you can creep the elegance a little bit further by also adding a class like this one:
/** This class encapsulates a feature that can be selectively disabled/enabled by putting an
* "enable_behavior_xxxx" or "disable_behavior_xxxx" file into the ~/MyProgram_Settings folder.
*/
class ConditionalBehavior
{
public:
/** Constructor.
* #param bugNumber Bug-Tracker ID number associated with this bug/feature.
* #param defaultState If true, this beheavior will be enabled by default (i.e. if no corresponding
* file exists in ~/MyProgram_Settings). If false, it will be disabled by default.
* #param switchAtVersion If specified, this feature's default-enabled state will be inverted if
* GetMyProgramVersion() returns any version number greater than this.
*/
ConditionalBehavior(int bugNumber, bool defaultState, int switchAtVersion = -1)
{
if ((switchAtVersion >= 0)&&(GetMyProgramVersion() >= switchAtVersion)) _enabled = !_enabled;
std::string fn = defaultState ? "disable" : "enable";
fn += "_behavior_";
fn += to_string(bugNumber);
if ((IsBehaviorFlagEnabled(fn))
||(IsBehaviorFlagEnabled("enable_everything")))
{
_enabled = !_enabled;
printf("Note: %s Behavior #%i\n", _enabled?"Enabling":"Disabling", bugNumber);
}
}
/** Returns true iff this feature should be enabled. */
bool IsEnabled() const {return _enabled;}
private:
bool _enabled;
};
Then, in your ExtensionsAPI.cpp file, you might have something like this:
// Extensions API feature is tracker #4321; disabled by default for now
// but you can try it out via "touch ~/MyProgram_Settings/enable_feature_4321"
static const ConditionalBehavior _feature4321(4321, false);
// Also tracker #4222 is now enabled-by-default, but you can disable
// it manually via "touch ~/MyProgram_Settings/disable_feature_4222"
static const ConditionalBehavior _feature4222(4222, true);
[...]
void DoTheExtensionsAPIStuff()
{
if (_feature4321.IsEnabled() == false) return;
[... otherwise do the extensions API stuff ...]
}
... or if you know that you are planning to make your Extensions API enabled-by-default starting with version 4500 of your program, you can set it so that Extensions API will be enabled-by-default only if GetMyProgramVersion() returns 4500 or greater:
static ConditionalBehavior _feature4321(4321, false, 4500);
[...]
... also, if you wanted to get more elaborate, the API could be extended so that IsBehaviorFlagEnabled() can optionally return a string to the caller containing the contents of the file it found (if any), so that you could do shell commands like:
echo "opengl" > ~/MyProgram_Settings/graphics_renderer
... to tell your program to use OpenGL for its 3D graphics, or etc:
// In Renderer.cpp
std::string rendererType;
if (IsDebugFlagEnabled("graphics_renderer", &rendererType))
{
printf("The user wants me to use [%s] for rendering 3D graphics!\n", rendererType.c_str());
}
else printf("The user didn't specify what renderer to use.\n");
I have one file "example.lua":
local function manipulate(something)
return string.rep(something, 3) -- repeats the given string
end
function apiFunction(somethingelse)
return manipulate(somethingelse)
end
and another files (main.lua) task is to "load"/"do" it:
loadAPI("example.lua", "externAPI") --< the part i need help with
externAPI.apiFunction("Test") --> should return TestTestTest
the thing that should happen is, that example.lua gets executed just like
dofile("example.lua")
but everything globally "defined" within example.lua (in this case the apiFunction) moves to the new generated global "externAPI" table and the rest (ie. manipulate) is hidden and only available from inside the example.lua file.
I've seen this bahaviour before in the minecraft mod "ComputerCraft" in which there is a function called "os.loadAPI("/somepath/sha-2") and it would define the definitions in the sha-2-chunk in the due to the name specified "sha-2"-table.
I've been searching for this sort of scoping/redirecting stuff for a while but there are no solutions putting the stuff into the new table.
I've been thinking of parsing the _G table after new indexes and move those to the new table but I'm sure there are some lua-magicians out here that know a much cleaner, better working solution to this.
All this is in one C lua_state* , so if there are any solutions adding this loadAPI function in C/C++ and just registrating it at the state this would be fine, too.
I've also looked at "require", but didn't seem to understand whether it does what I need.
Using Lua 5.2.3
Hope i didn't forget anything.
Thanks in advance :)
~InDieTasten
Try this:
function loadAPI(f,g)
_G[g]=setmetatable({},{__index=_G})
loadfile(f,"bt",_G[g])()
end
loadAPI("example.lua", "externAPI")
print(externAPI.apiFunction("Test"))
I'm testing a function that may modify a file. How do i test that it is unchanged in the cases where I want it to?
I don't want to check the content, because the file may have been overwritten with the same content, changing the modification time.
I can't really check the modification time, either. Since I like tests to be self-contained, the original file would be written just before the (non-)modification test, rendering the modification time unreliable.
You can use DI to mock your filewriter. This way you do not need the file at all, only check if the write function is called and you know if the file was modified.
I would split the function into two separate functions; the first decides whether the modification should be made, the second makes the notification. The second is only called if necessary. In pretend language:
function bool IsModificationRequired()
{
// return true or false based on your actual code
}
function void WriteFile()
{
new File().Write("file");
}
function void WriteIfModified()
{
if (IsModificationRequired())
WriteFile();
}
And test
Assert.IsTrue(IsModificationRequired());
Well assuming you are using a text file and reasonable size. Just hash the file content, if before modify and after modidfy hashcode is same then - it means the file content is not changed.
Here is the link to Algorithim Design Manual - Steve Skiena (Google Book Result)
Section 3.8
How can i convicne you that a file isn't changed ?