I'm designing an interface that can be used to report errors in C++. (I'm working with a legacy system where exceptions are out of question.) In my youthful naivety, I started along these lines while designing my API:
bool DoStuff(int amount, string* error);
Return value signals success/failure, while error is used to report a human readable explanation. So far so good. Subroutine calls passed along the error pointer and everything was hunky-dory.
I ran into the following problems with this design (so far):
Cannot report warnings.
Not thread-safe.
Next, I decided to go with the following interface, instead of plain string:
class Issues {
public:
void Error(const string& message);
void Warning(const string& message);
void Merge(const Issues& issues);
}
So that I can change my API like this:
bool DoStuff(int amount, Issues* issues);
I'm wondering, is there a more generic/standard API out there that deals with this problem? If yes, I'd like to take a look.
UPDATE: I'm not looking for a logging library. For those who are curious, imagine you're writing a query engine that includes a compiler. The compiler issues warnings and errors, and those need to be returned to the user, as part of the response. Logging has its place in the design, but this is not it.
I usually use things like boost::signals or .NET delegates to report errors/warning/logging/whatever. You report errors with no changes to the interface, and the library user plugs whatever she wants to the signal to get the error reports (writing to a file, updating a console window, aborting the program, throwing an exception, ignoring warnings, etc).
Something like this, at eg. global scope:
boost::signal<void(std::string const&)> logError;
boost::signal<void(std::string const&)> logWarning;
and then
void routineWhichMayFail()
{
...
if (answer != 42)
{
logError("Universal error");
return;
}
}
and you connect something to logError and logWarning at initialization:
void robustErrorHandler(std::string const& msg)
{
std::cerr << "Error: " << msg << "\n";
std::exit(EXIT_FAILURE);
}
void initializeMyProgram()
{
logError.connect(&robustErrorHandler);
}
You can even throw exceptions in the error handler instead of exiting, and use fancier things than bare functions (logging classes, "delegates" -- pointers to methods with a this object bundled, RPC to a distant server). This way, you decouple the error handling from error reporting, which is good. You can also report to multiple destinations, you can even have your handlers return a boolean telling whether the action should be eg. retried.
From your explanation it sounds like you are trying to implement a logging library for your project. You can look at log4cpp or Boost.Log.
Related
Suppose I have this in a custom Stack implementation:
void Pop (Stack & s) {
assert (!isEmpty(s));
// implementation details of popping omitted
}
Suppose I want to catch bad client uses like popping an empty stack. "Assert" is great until you compile the production version and disable it via the NDEBUG flag. What's the most professional way of dying gracefully if you detect an unrecoverable error, assuming that you are going to turn off assertions eventually?
Yes, I know there are a bunch of options: use "exit"; change the function to return a C-like error code; use C++ exception handling; just ignore the offending operation (make bad calls into a no-op); implement a personal version assert called something else that won't get turned off, etc.
What the "most pro" thing to do here? I just want to die quickly, with a helpful message.
For fun, I created a vector instance from the standard library and popped it empty. This caused a seg fault, which might be acceptable for the standard library, but I want to catch and report such a problem before dying.
It is often used self defined assert macro with logging in production code. For example,
#define MYCOMPANY_ASSERT_FATAL(expression, msg, ret_val) if (!expression){ logger.fatal(msg); return ret_val;}
#define MYCOMPANY_ASSERT_WARN(...) .....
#define MYCOMPANY_ASSERT_ERROR(...) .....
Basically, the severity level of the error which should be regarded as exiting or messaging or so is dependent on your application program context layer. In short, some_lib_func() couldn't decide to exit an own process in most cases. That's why some_lib_func() should propagate the error information to caller. For example,
// library or middle module func couldn't decide to handle own application process, so after only logging return to caller
bool read_csv(double& val) {
double val = 0;
bool ret = parse_csv_from_file(val);
MYCOMPANY_ASSERT_ERROR(ret, "failed to parse_csv_from_file", false);
// return to caller with logging and error info(true/false here)
....
....
}
// application layer and need to handle for error which should be continue or message for user..
bool show_weather_in_foreign_country() {
bool ret = read_csv();
if (!ret) {
show_error_message();
}
// in this case read_csv error is trivial and you want to continue to process with proper message
...
}
In this case, showing weather is considered as trivial process in your application and you don't want to exit a whole application if error, so after showing a appropriate message and continue to process. In the other hand, another case below is critical, despite using the same function of read_csv.
// application layer and need to handle for error which should be continue or message for user..
bool send_your_account_balance_in_securiities_to_your_wife() {
double val = 0;
bool ret = read_csv(val);
MYCOMPANY_ASSERT_FATAL(ret, "critical in my account balance", false);
// in this application context, the failure of read_csv is critical and never continue to process
// and return to caller. Caller should probably exit an own application
send_email_your_wife(val);
// if send 0$ with some kind of mistake to you wife, she might die or kill you ...
...
}
Therefore, preparing some of defined macro for propagating error and logging is so useful and make your code simple and safe, and then you need to use them properly depending on your application contexts.
I'm trying to implement a very simple, local, HTTP server for my C++ application — I'm using XCode on macOS. I have to implement it from within a dynamically loaded library rather than the "main" thread of the program. I decided to try using boost::beast since another part of the application uses boost libraries already. I'm trying to implement this example, but within the context of my library, and not as part its main program.
The host application for this library calls on the following function to start a localhost server, but crashes when instantiating "acceptor":
extern "C" BASICEXTERNALOBJECT_API long startLocalhost(TaggedData* argv, long argc, TaggedData * retval) {
try {
string status;
retval->type = kTypeString;
auto const address = net::ip::make_address("127.0.0.1");
unsigned short port = static_cast<unsigned short>(std::atoi("1337"));
net::io_context ioc{1};
tcp::acceptor acceptor{ioc, {address, port}}; // <-- crashes on this line
tcp::socket socket{ioc};
http_server(acceptor, socket);
ioc.run();
status = "{'status':'ok', 'message':'localhost server started!'}";
retval->data.string = getNewBuffer(status);
}
catch(std::exception const& e)
{
string status;
//err_msg = "Error: " << e.what() << std::endl;
status = "{'status':'fail', 'message':'Error starting web server'}";
retval->data.string = getNewBuffer(status);
}
return kESErrOK;
}
When stepping through the code, I see that XCode reports an error when the line with tcp::acceptor ... is executed:
Thread 1: EXC_BAD_ACCESS (code=1, address=0x783c0a3e3f22650c)
and is highlighted at the single line of code in a function in scheduler.h:
//Get the concurrency hint that was used to initialize the scheduler.
int concurrency_hint() const
{
return concurrency_hint_; //XCode halts here
}
I'm debating as to whether or not I should include a different C++ web server, like Drogon, instead of boost::beast, but I thought I would post here to see if anybody had any insight as to why the crash is happening in this case.
Update
I found a fix that is a workaround for my particular circumstances, hopefully it can help others running into this issue.
The address to the service_registry::create static factory method resolves correctly when I add ASIO_DECL in front of the methods declaration in asio/detail/service_registry.hpp.
It should look like this:
// Factory function for creating a service instance.
template <typename Service, typename Owner>
ASIO_DECL static execution_context::service* create(void* owner);
By adding ASIO_DECL in front of it, it resolves correctly and the scheduler and kqueue_reactor objects initialize properly avoiding the bad access to concurrency_hint().
In my case I am trying to use non-Boost ASIO inside of a VST3 audio plug-in running in Ableton Live 11 on macOS on an M1 processor. Using the VST3 plug-in in I'm getting this same crash. Using the same plug-in in other DAW applications, such as Reaper, does not cause the crash. It also does not occur for Ableton Live 11 on Windows.
I've got it narrowed down to the following issue:
In asio/detail/impl/service_registry.hpp the following method attempts to return a function pointer address to a create/factory method.
template <typename Service>
Service& service_registry::use_service(io_context& owner)
{
execution_context::service::key key;
init_key<Service>(key, 0);
factory_type factory = &service_registry::create<Service, io_context>;
return *static_cast<Service*>(do_use_service(key, factory, &owner));
}
Specifically, this line: factory_type factory = &service_registry::create<Service, io_context>;
When debugging in Xcode, in the hosts that work, when inspecting
factory, it shows the correct address linking to the service_registry::create<Service, io_context> static method.
However, in Ableton Live 11, it doesn't point to anything - somehow the address to the static method does not resolve correctly. This causes a cascade of issues, ultimately leading up to trying to invoke the factory function pointer in asio/asio/detail/impl/service_registry.ipp in the method service_registry::do_use_service. Since it doesn't point to a proper create method, nothing is created, it results in uninitialized objects, including the scheduler instance.
Therefore, when calling scheduler_.concurrency_hint() in kqueue_reactor.ipp the scheduler is uninitialized, and the EXC_BAD_ACCESS error results.
It's unclear to me why under some host processes, dynamically loading the plug-in cannot resolve the static method address, but others have no problem. In my case I compiled asio.hpp for standalone ASIO into the plug-in directly, there was no linking.
The best guesses I can come up with are
maybe your http_server might start additional threads or even fork. This might cause io_context and friends to be accessed after startLocalhost returned. To explain the crash location appearing to be at the indicated line, I could add the heuristic that something is already off during the destructor for ioc
the only other idea I have is that actually the opening/binding of the acceptor throws, but due to possible incompatibilities of types in the shared module vs the main program, the exception thrown is not actually caught and causes abnormal termination. This might happen more easily if the main program also uses Boost libraries, but a different copy (build/version) of them.
In this case there's a simple thing you can do: split up initialization and use the overloads that take error_code to instead use them.
I am working on a hobby project mainly to learn cpp unit testing and database programming. However I am a little bit lost & confused about how should I write my code for proper testing. I tend to write a lot of void functions for my cpp projects. But now I can not figure out how should I test those functions. I have been succeeded in testing non-void functions cause they return something which can be easily tested against a value.
Ami I doing things in an unprofessional way? Should I avoid void functions as much as possible so that I can test those functions ? Or I am missing something ? For example how would I be able to test this function -
database.cpp
#include "database.hpp"
#include <sqlite3.h>
#include <iostream>
#include "spdlog/sinks/basic_file_sink.h"
// Creating the logging object
auto logger = spdlog::basic_logger_mt("appnotex", "../data/appnotexlog");
void Database::createDb(const char *dbname) {
// Creating the database file
sqlite3 *datadb;
int status = sqlite3_open(dbname, &datadb);
// checking for errors
if (status == SQLITE_OK) {
logger->info("------------ New Session ----------");
logger->info("Connected to Database Successfully");
} else {
std::string errorMessage = sqlite3_errmsg(datadb);
logger->info("Error: " + errorMessage);
}
If Needed
I am using Google Test framework
My whole project code hosted - here
Update
I have tried this one is this approach of testing the above method correct ?
databaseTest.cpp
TEST(DatabaseTest, createDbTest) {
const char *dbfilename = "../data/test/data.db";
const char *tbname = "DataTest";
Database *db = new Database();
std::ifstream dbfile("../data/test/data.db");
bool ok = false;
if (!dbfile.is_open())
ok = false;
else
ok = true;
EXPECT_TRUE(ok);
}
The problem is not so much in the function returning void. Think about how it signals errors and make sure all cases (success and failures) are tested, simple as that.
However, I don't see any error signalling at all there, apart from logging it. As a rule of thumb, logging should only be used for post-mortem research and the like. So, if logging completely fails, your program can still run correctly. That means, nothing internally depends on it and it is not a suitable error handling/signalling mechanism.
Now, there are basically three ways to signal errors:
Return values. Typically used in C code and sometimes used in C++ as well. With void return, that's not an option, and that is probably the source of your question.
Exceptions. You could throw std::runtime_error("DB connect failed"); and delegate handling it to the calling code.
Side effects. You could store the connection state in your Database instance. For completeness, using a global errno is also possible, but not advisable.
In any case, all three ways can be exercised and verified in unit tests.
I have been researching both the C++ (or Windows API) method for creating a socket, and the .Net method for creating a socket. My concern is whether the same error codes that are available in Windows sockets are also available in the .Net Socket class. I have looked at this page on "Windows Sockets Error Codes" and also this page, which describes the error codes for the .Net Socket class.
After looking at both of the above pages, it seems that the .Net Socket class provides just as much in regards to socket error reporting as the Windows API. I would prefer to use .Net to implement a Socket due to the fact that I feel it would be easier for me as someone who does not have a wide range of knowledge when it comes to C++ and network programming. However, this job requires that I be able to report errors of the same granularity as the Windows API.
I'm trying to be as specific as possible here, but with the information provided, what can you tell me in regards to comparing the two with error codes in mind? With my knowledge, I am thinking that the C# Socket class is just as strong in this aspect as the Windows API.
If you receive a SocketException in .NET the exception has a property called ErrorCode which maps to all of the values you posted in your first link.
So both API's are just as granular in their error reporting. The enum you linked to is just for convince so you don't need to make your own constants for the more popular error codes.
const int WSA_E_NO_MORE= 10110;
const int WSAEACCES = 10013;
void Foo()
{
try
{
//...
}
catch(SocketException ex)
{
// These two lines are equivalent.
//if(ex.ErrorCode == WSAEACCES)
if(ex.ErrorCode == SocketError.AccessDenied)
{
//Do something special for access denied.
}
else if(ex.ErrorCode == WSA_E_NO_MORE)
{
//Do something special with the WSA_E_NO_MORE error code
}
}
}
If you want a easy way to see which enum maps to which error code exactly the reference source shows what native constant each enum represents.
Edit:
For personn interested in a cleaner way to implemenent that, have a look to that answer.
In my job I often need to use third-made API to access remote system.
For instance to create a request and send it to the remote system:
#include "external_lib.h"
void SendRequest(UserRequest user_request)
{
try
{
external_lib::Request my_request;
my_request.SetPrice(user_request.price);
my_request.SetVolume(user_request.quantity);
my_request.SetVisibleVolume(user_request.quantity);
my_request.SetReference(user_request.instrument);
my_request.SetUserID(user_request.user_name);
my_request.SetUserPassword(user_request.user_name);
// Meny other member affectations ...
}
catch(external_lib::out_of_range_error& e)
{
// Price , volume ????
}
catch(external_lib::error_t& e)
{
// Here I need to tell the user what was going wrong
}
}
Each lib's setter do checks the values that the end user has provided, and may thow an exception when the user does not comply with remote system needs. For instance a specific user may be disallowed to send a too big volume. That's an example, and actually many times users tries does not comply: no long valid instrument, the prices is out of the limit, etc, etc.
Conseqently, our end user need an explicit error message to tell him what to modify in its request to get a second chance to compose a valid request. I have to provide hiim such hints
Whatever , external lib's exceptions (mostly) never specifies which field is the source
of aborting the request.
What is the best way, according to you, to handle those exceptions?
My first try at handling those exceptions was to "wrap" the Request class with mine. Each setters are then wrapped in a method which does only one thing : a try/catch block. The catch block then throws a new exceptions of mine : my_out_of_range_volume, or my_out_of_range_price depending on the setter. For instance SetVolume() will be wrapped this way:
My_Request::SetVolume(const int volume)
{
try
{
m_Request.SetVolume(volume);
}
catch(external_lib::out_range_error& e)
{
throw my_out_of_range_volume(volume, e);
}
}
What do you think of it? What do you think about the exception handling overhead it implies? ... :/
Well the question is open, I need new idea to get rid of that lib constraints!
If there really are a lot of methods you need to call, you could cut down on the code using a reflection library, by creating just one method to do the calling and exception handling, and passing in the name of the method/property to call/set as an argument. You'd still have the same amount of try/catch calls, but the code would be simpler and you'd already know the name of the method that failed.
Alternatively, depending on the type of exception object that they throw back, it may contain stack information or you could use another library to walk the stack trace to get the name of the last method that it failed on. This depends on the platform you're using.
I always prefer a wrapper whenever I'm using third party library.
It allows me to define my own exception handling mechanism avoiding users of my class to know about external library.
Also, if later the third party changes the exception handling to return codes then my users need not be affected.
But rather than throwing the exception back to my users I would implement the error codes. Something like this:
class MyRequest
{
enum RequestErrorCode
{
PRICE_OUT_OF_LIMIT,
VOLUME_OUT_OF_LIMIT,
...
...
...
};
bool SetPrice(const int price , RequestErrorCode& ErrorCode_out);
...
private:
external_lib::Request mRequest;
};
bool MyRequest::SetPrice(const int price , RequestErrorCode& ErrorCode_out)
{
bool bReturn = true;
try
{
bReturn = mRequest.SetPrice(price);
}
catch(external_lib::out_of_range_error& e)
{
ErrorCode_out = PRICE_OUT_OF_LIMIT;
bReturn = false;
}
return bReturn;
}
bool SendRequest(UserRequest user_request)
{
MyRequest my_request;
MyRequest::RequestErrorCode anErrorCode;
bool bReturn = my_request.SetPrice(user_request.price, anErrorCode);
if( false == bReturn)
{
//Get the error code and process
//ex:PRICE_OUT_OF_LIMIT
}
}
I think in this case I might dare a macro. Something like (not tested, backslashes omitted):
#define SET( ins, setfun, value, msg )
try {
ins.setfun( value );
}
catch( external::error & ) {
throw my_explanation( msg, value );
}
and in use:
Instrument i;
SET( i, SetExpiry, "01-01-2010", "Invalid expiry date" );
SET( i, SetPeriod, 6, "Period out of range" );
You get the idea.
Although this is not really the answer you are looking for, but i think that your external lib, or you usage of it, somehow abuses exceptions. An exception should not be used to alter the general process flow. If it is the general case, that the input does not match the specification, than it is up to your app to valid the parameter before passing it to the external lib. Exceptions should only be thrown if an "exceptional" case occurrs, and i think whenever it comes to doing something with user input, you usually have to deal with everything and not rely on 'the user has to provide the correct data, otherwise we handle it with exceptions'.
nevertheless, an alternative to Neil's suggestions could be using boost::lambda, if you want to avoid macros.
In your first version, you could report the number of operations that succeeded provided the SetXXX functions return some value. You could also keep a counter (which increases after every SetXXX call in that try block) to note what all calls succeeded and based on that counter value, return an appropriate error message.
The major problem with validating each and every step is, in a real-time system -- you are probably introducing too much latency.
Otherwise, your second option looks like the only way. Now, if you have to write a wrapper for every library function and why not add the validation logic, if you can, instead of making the actual call to the said library? This IMO, is more efficient.