First, this is being built on Linux.
We have an API that is based on wxObjects (we do not use the GUI objects). Our classes are defined as follows:
#include <wx/wx.h>
class apibaseclass : public wxObject
{
apibaseclass();
~apibaseclass();
}
About five years ago this compiled and linked just fine. I've been asked to make changes and now I get the following error:
undefined reference to wxObject::wxObject()'/home/lloyd/Projects/wxtestprogram/main.cpp:7: undefined reference towxObject::wxObject()'
This is the program I was using as a sanity test:
#include <iostream>
#include <wx/wx.h>
class blah : public wxObject
{
public:
int x;
blah();
virtual ~blah();
void setvalue(int value);
int getvalue();
};
blah::blah()
{
}
blah::~blah()
{
}
void blah::setvalue(int value)
{
x = value;
}
int blah::getvalue()
{
return x;
}
using namespace std;
int main()
{
class blah *testvalue = new blah();
testvalue->setvalue(15);
wxPrintf(wxT("Hello World 2 %d\r\n"), testvalue->getvalue());
wxString str1 = wxT("Linux");
wxString str2 = wxT("Operating");
wxString str3 = wxT("System");
wxString str;
str = str1 + wxT(" ") + str2 + wxT(" ") + str3;
wxPuts(str);
wxPrintf(wxGetHomeDir());
long int mem = wxGetFreeMemory();
wxPrintf(wxT("Memory: %ld\n"), mem);
return 0;
}
What is bothersome is that if I replace "public wxObject" with "public wxString" then it links just fine. Why am I unable to access wxObject?!?
NOTE: I've never linked against anything other than libwx_baseu-2.6.so in the past. And in fact when I build without the GUI it only builds libwx_baseu-2.6, libwx_baseu_net-2.6 and libwx_baseu_xml-2.6.
What do I need to do to get things building and LINKING again with minimal muss and fuss?
Using
wx-config --cxxflags --libs base
gave me the missing items that allowed me to build the project correctly. No doubt this is what I used five years ago.
Related
Why does this not compile? The marked line gives me: "static assertion failed: The parser expects tuple-like attribute type". I would think that an std::tuple were the essence of "tuple-like"?
#include <string>
#include <tuple>
#include <boost/spirit/home/x3.hpp>
void parseInteger(std::string input) {
namespace x3 = boost::spirit::x3;
auto iter = input.begin();
auto end_iter = input.end();
int result;
x3::parse(iter, end_iter, x3::int_, result);
}
void parseIntegerAndDouble(std::string input) {
namespace x3 = boost::spirit::x3;
auto iter = input.begin();
auto end_iter = input.end();
std::tuple<int, double> result;
x3::parse(iter, end_iter, x3::int_ >> ' ' >> x3::double_, result); //Compile error!
}
int main(int, char **)
{
parseInteger("567");
parseIntegerAndDouble("321 3.1412");
return 0;
}
The trick is to include two additional header files:
#include <boost/fusion/adapted/std_tuple.hpp>
#include <boost/fusion/include/std_tuple.hpp>
This is a bit more magical than I like, but I've got a feeling I really don't want to know how this works!
I have this code in CLI
List<Codec^> ^GetCodecs()
{
List<Codec^> ^l = gcnew List<Codec^>;
bool KeepLooping = Encoder_MoveToFirstCodec();
while (KeepLooping)
{
Codec ^codec = gcnew Codec(); // here... and that call encoder_init many times... which call register codec many times... which is a mass...
codec->Name = gcnew String(Encoder_GetCurrentCodecName());
codec->Type = Encoder_GetCurrentCodecType();
char pix_fmts[200]; // array of 200 is probably enough
int actual_pix_fmts_sz = Encoder_GetCurrentCodecPixFmts( pix_fmts , 200 );
for (int i = 0 ; i < actual_pix_fmts_sz ; i++)
{
//copy from pix_fmts to the :List
codec->SupportedPixelFormats->Add(pix_fmts[i]);
}
This is the Encoder_GetCurrentCodecPixFmts function in C:
int Encoder_GetCurrentCodecPixFmts( char *outbuf , int buf_sz )
{
int i=0;
while ( (i<buf_sz) && (codec->pix_fmts[i]!=-1) )
{
outbuf[i] = codec->pix_fmts[i];
i++;
}
return i;
}
This is a new class i did:
#pragma once
using namespace System;
using namespace System::Collections::Generic;
public ref class Codec
{
public:
String^ Name;
int ID; // this is the index
int Type; // this is the type
List<int> ^SupportedPixelFormats;
Codec(void)
{
SupportedPixelFormats = gcnew List<int>;
// do nothing in the constructor;
}
};
Which contain also the: SupportedPixelFormats
The constructor in this new class should be empty but i needed somewhere to make an instance for the List make a NEW for the List.
Now in the C++ i need to transfer from pix_fmts char array to codec->Supported
Or to copy from pix_fmts to the :List
So i did as above:
codec->SupportedPixelFormats->Add(pix_fmts[i]);
But i'm not sure if this the meaning of copy.
Is that right what i did ?
It works, it's a kind of a deep copy. What makes you think it doesn't work? Do the results turn out wrong? If they do, put a breakpoint in there and try to get what is wrong.
Instead of copying one by one perhaps you can use the Enumerable::ToList extension method.
I hope this helped you.
For boost::serialize I am trying to define a custom class with its own serialize function, similar to http://www.boost.org/doc/libs/1_53_0/libs/serialization/doc/tutorial.html#simplecase However, the program just segfaults. Why?
class Test {
public:
unsigned short testid;
template<class Archive>
void serialize(Archive & ar, const unsigned int version)
{
ar & testid;
}
};
int main() {
Test mytest = {100};
std::ofstream ofsx("test.tmp");
boost::archive::binary_oarchive oax(ofsx);
oax << mytest;
cout << "Exported";
exit(1);
}
I also tried the non-intrusive version with the same result.
Am I missing something?
The problem was caused by linking against outdated libraries.
Suppose I have two classes:
class1 {
int m_i;
std::string m_s;
};
class2 {
int m_i2;
class1 *m_ptr;
};
Now, I want to send a class2 variable over network, and want to use any of the libraries that does serialization.(Protocol-buffers, Thrift, MessagePack..)
Which one can I use?(note the class1* m_ptr)
You could use thrift for this.
the definition would look something like
struct class1 {
1: required i32 m_i;
2: required string m_s;
}
struct class2 {
1: required i32 m_i2;
2: optional class1 m_ptr;
}
You would like to read this excellent guide
http://diwakergupta.github.com/thrift-missing-guide/
and to get clarity on concern about the "pointer" issue that you mentioned in the question,read the section on "How are nested structs initialized?" in the above guide.
Using google protocol buffers, you would need a .proto file (say test.proto) like:
package serialisation; // puts this in namespace serialisation
message class1 {
required int32 m_i = 1;
required bytes m_s = 2;
}
message class2 {
required int32 m_i2 = 1;
optional class1 m_ptr = 2;
}
Using C++, once you run the protoc compiler against this, you end up with test.pb.cc and test.pb.h
You can then use these like:
#include <string>
#include "test.pb.h"
struct class1 {
int m_i;
std::string m_s;
};
struct class2 {
int m_i2;
class1 *m_ptr;
};
int main() {
class2 second_class;
second_class.m_i2 = 2;
second_class.m_ptr = new class1;
second_class.m_ptr->m_i = 1;
second_class.m_ptr->m_s = "one";
// Serialise class 2
serialisation::class2 serialisable_second_class;
serialisable_second_class.set_m_i2(second_class.m_i2);
if (second_class.m_ptr) {
serialisation::class1* serialisable_first_class = serialisable_second_class.mutable_m_ptr();
serialisable_first_class->set_m_i(second_class.m_ptr->m_i);
serialisable_first_class->set_m_s(second_class.m_ptr->m_s);
}
std::string serialised(serialisable_second_class.SerializeAsString());
// Parse class 2
serialisation::class2 parsed_second_class;
parsed_second_class.ParseFromString(serialised);
class2 retrieved_second_class;
retrieved_second_class.m_i2 = parsed_second_class.m_i2();
if (parsed_second_class.has_m_ptr()) {
retrieved_second_class.m_ptr = new class1;
retrieved_second_class.m_ptr->m_i = parsed_second_class.m_ptr().m_i();
retrieved_second_class.m_ptr->m_s = parsed_second_class.m_ptr().m_s();
} else {
retrieved_second_class.m_ptr = nullptr;
}
return 0;
}
Note, for the sake of brevity I'm not doing any error checking or exception handling here - this would be needed in production code. I'm also not managing the lifetime of the class1 pointer.
What are they, what's the different between them?
Many sources, like Wikipedia, claim they're the same thing, but others explicitly say the opposite, like sbi in this question:
First: "Visitor Pattern is a way to simulate Double Dispatching in C++." This is, erm, not fully right. Actually, double dispatch is one form of multiple dispatch, which is a way to simulate (the missing) multi-methods in C++.
They are the same.
When you call a virtual method in C++, the actual method to run is based on the runtime type of the object them method is invoked on. This is called "single dispatch" because it depends on the type of a single argument (in this case, the implicit 'this' argument). So, for example, the following:
class Base {
public:
virtual int Foo() { return 3; }
}
class Derived : public Base {
public:
virtual int Foo() { return 123; }
}
int main(int argc, char *argv[]) {
Base* base = new Derived;
cout << "The result is " << base->Foo();
delete base;
return 0;
}
When run, the above program prints 123, not 3. So far so good.
Multiple-dispatch is the ability of a language or runtime to dispatch on both the type of the 'this' pointer and the type of the arguments to the method. Consider (sticking with C++ syntax for the moment):
class Derived;
class Base {
public:
virtual int Foo(Base *b) { cout << "Called Base::Foo with a Base*"; }
virtual int Foo(Derived *d) { cout << "Called Base::Foo with a Derived*"; }
}
class Derived : public Base {
public:
virtual int Foo(Base *b) { cout << "Called Derived::Foo with a Base*"; }
virtual int Foo(Derived *d) { cout << "Called Derived::Foo with a Derived*"; }
}
int main(int argc, char *argv[]) {
Base* base = new Derived;
Base* arg = new Derived;
base->Foo(arg);
delete base;
delete arg;
return 0;
}
If C++ had multiple-dispatch, the program would print out "Called Derived::Foo with a Dervied*". (Sadly, C++ does not have multiple-dispatch, and so the program prints out "Called Derived::Foo with a Base*".)
Double-dispatch is a special case of multiple-dispatch, often easier to emulate, but not terribly common as a language feature. Most languages do either single-dispatch or multiple-dispatch.