I am trying to understand how to best make use of blocks in my templated class.
I have the following code snippet:
template<typename T, typename R>
class MyClass {
public:
typedef R (^Block)(T);
MyClass(Block blk) {}
};
void testMyClass() {
MyClass<int,int>::Block blk(^(int arg) {
return 1 + arg;
});
}
When I try to compile this, I get the following error message:
error: cannot convert ‘int (^)(int)’ to ‘R (^)(T)’ in initialization
Am I missing something obvious? Am I trying to do something that is not allowed? GCC accepts the program if I do the same thing without templates.
This is an issue in GCC. I tested your program under LLVM 3 and it compiled just fine.
There are a number of problems in GCC 4.2's implementation of blocks, sometimes they can be worked around by fully qualifying your block declarations ^int(int arg){return 1 + arg;} but in this case it was unable to work around this issue. I would highly recommend moving to use LLVM/Clang for any further work with Obj-C Blocks. Its C++ support is very good these days, especially for C++03 support.
Related
The following code gives compilation errors on both MSVC++ 2012 CTP (with C+11 support) and Intel C++ XE 13.0:
template <typename F, typename... Args>
void apply(F f, std::tuple<Args...>& args) {
// doesn't do much yet
}
bool f1(char c) {
return c == 'c';
}
int main(int argc, char* argv[]) {
auto t = std::make_tuple('c');
apply(f1, t);
return 0;
}
VS2012 error is:
error C2243: 'type cast' :
conversion from 'std::tuple<char,std::_Nil,std::_Nil,std::_Nil,std::_Nil,std::_Nil,std::_Nil,std::_Nil> *'
to 'std::tuple<std::_Nil,std::_Nil,std::_Nil,std::_Nil,std::_Nil,std::_Nil,std::_Nil,std::_Nil> &' exists,
but is inaccessible
Error on Intel C++ XE 13.0 is:
error : no instance of function template "apply" matches the argument list
What am I missing? Are there really errors here, or do I just have two bad compilers?
UPDATE: Same (or similar) results when I use boost::tuple instead of std::tuple on both compilers.
ADDENDUM: Thanks for all the cross-checks in the comments. I've sent bug reports to both of these fine corporations.
That is likely a VC11 bug in the implementation of the Standard Library. Although the CTP supports variadic templates, to the best of my knowledge the Standard Library was not rewritten to use them and adopts some machinery to simulate variadic templates. This is likely at the origin of your problem.
I have a problem compiling a c++ program with gcc version 4.6.3; I can compile this program with microsoft compiler (v 9.0) without problems.
This program is using some of my libraries I always used with microsoft compiler.
problem is when I try to pass a reference as argument that is a subtype of another: pseudo example here:
class ObjManager{..}
class SubObjMng : public ObjManager{
public:
inline SubObjMng() : ObjManager(0, ... ){}
};
class Test{
public:
Test(int i, ObjManager &obj_mng);
}
int main(){
SubObjMng myobjmng;
Test t(0, myobjmng); //GCC ERROR HERE
}
output of the error is (real output for my program):
globals.h:227:40: error: no matching function for call to cdk::HashMap::HashMap(unsigned int, cdk::PtrObjMng, cdk::cstrObjMng)
globals.h:227:40: note: candidates are:
contrib/cdklib/cdk_struct.h:485:12: note: cdk::HashMap::HashMap(uint32_t, cdk::ObjManager&, cdk::ObjManager&)
contrib/cdklib/cdk_struct.h:485:12: note: no known conversion for argument 2 from cdk::PtrObjMng to cdk::ObjManager&
anyone can help?
thanks!
cdk::PtrObjMng should inherit from cdk::ObjMng, making polymorphism possible through references. Otherwise this is a no-go according to what the compiler says.
Of course this might not be the root of your problem, I wish we could see the implementation of your constructor.
When I compile this code:
template<typename T>
struct S {
std::vector<T> v;
S(initializer_list<T> l) : v(l) {
std::cout << "constructed with a " << l.size() << "-element list\n";
}
};
using the following command line:
clang++ -std=c++11 -stdlib=libc++ initializer_list.cpp
I get the following error.
initializer_list.cpp:12:23: error: expected ')'
S(initializer_list<T> l) : v(l) {
Does anyone know the fix if any??
Thanks in advance
You probably meant to write std::initializer_list<T>. Make sure you include <initializer_list>.
Your code sample is incomplete. It would be useful if you can provide a complete example. The problem with the code as written is that you're missing
#include <initializer_list>
#include <vector>
#include <iostream>
... and initializer_list is in namespace std, so you're also missing a std:: from your constructor declaration.
However, since you've claimed that neither of these is the issue, the most likely cause would seem to be that your C++ standard library implementation doesn't provide std::initializer_list. That would be the case if Clang is using GCC's libstdc++, and you do not have a suitably new version of that installed: you need at least version 4.4, but note that a patch is required to fix bugs in libstdc++-4.4 in order to make it work with Clang in C++11 mode, otherwise you will get errors about type_info and various other problems.
Also, you say that the diagnostic you received is this:
initializer_list.cpp:12:23: error: expected ')'
S(initializer_list<T> l) : v(l) {
^
(I've reconstructed the caret from the provided column number; it would be useful to preserve it in future questions.) For any of the above explanations, this will not be the first diagnostic which Clang produces; that would be something along the lines of:
initializer_list.cpp:12:5: error: no template named 'initializer_list'; did you mean 'std::initializer_list'?
S(initializer_list<T> l) : v(l) {
^~~~~~~~~~~~~~~~
std::initializer_list
So either you've missed out the first diagnostic from your question, or the problem is that you have declared some other (non-template) type named initializer_list in the code you omitted in your question, and that is hiding std::initializer_list. Without seeing the rest of your code or the rest of your diagnostics, it's not possible to tell which.
I am a avid emacs user, and want to use sgml markup check routine.
I was naturally headed towards nsgmls, and downloded the source code to compile it.
However, there was a strange error coming from the compiler with the followings.
./../include/RangeMap.h:57: error: type ‘Vector<RangeMapRange<From, To> >’ is not deri ved from type ‘RangeMapIter<From, To>’
./../include/RangeMap.h:57: error: expected ‘;’ before ‘ptr_’
./../include/RangeMap.h: In member function ‘Boolean RangeMapIter<From, To>::next(From&, From&, To&)’:
./../include/RangeMap.h:47: error: ‘ptr_’ was not declared in this scope
I know that some times compiler gets disgruntled by template and typename madness, however the codes seems to have already used typename correctly within the code.
Here are the cope snippets that arouses these errors.
template<class From, class To>
class RangeMapIter {
public:
RangeMapIter(const RangeMap<From,To> &map);
Boolean next(From &fromMin, From &fromMax, To &toMin) {
if (!count_)
return 0;
else {
fromMin = ptr_->fromMin;
fromMax = ptr_->fromMax;
toMin = ptr_->toMin;
ptr_++;
count_--;
return 1;
}
}
private:
size_t count_;
typename Vector<RangeMapRange<From,To> >::const_iterator ptr_;
};
Can anybody help me hash out those errors?
This error message is given by GCC in the wrong order of both type names. (but it apparently fixed this in the latest version). It is meant to say that Vector<RangeMapRange<From,To> >::const_iterator was not found to be a type name. The underlying cause of this diagnostic is that the code is parsed as an access-declaration, which has the following syntax
::[opt] nested-name-specifier template[opt] unqualified-id ;
An example of that syntax
struct A {
int a;
};
struct B : A {
// equivalent to: using A::a;
A::a;
};
In C++11 this access-declaration construct was taken out of the specification and it was deprecated in C++03. But since the compiler still supports parsing it, when the Vector<RangeMapRange<From,To> >::const_iterator is not found to be a type, it will be taken as a name to be declared in an access-declaration (so the parser moves forward across the type specifier section). Hence according to the above syntax, after the unqualified-id which in this case is const_iterator (and in my example was a), it wants to see a semicolon and it wants that Vector<RangeMapRange<From, To> > is a base class of RangeMapIter<From, To>, but confusingly the diagnostic it gives has it the other way around.
Check your names and make sure the type exists.
FC++ is a library for functional programming in C++. I am using it on MinGW with gcc 4.5.0. When I use the more basic features, I have no problems. But one of the more advanced features is giving me a template-related error (or maybe there's just a problem with my code...couldn't be!).
Does anybody have FC++ working with 4.5.0? See anything wrong with my code?
The link text is solidly out of date, though it shows a history of issues with gcc and template specialization. The link text isn't more up to date.
Here's my code:
#include <iostream>
#include "prelude.h"
using namespace fcpp;
using namespace std;
struct TwoTimes {
template <class T>
struct Sig : public FunType<T,T> {};
template <class F>
F operator() (const F& x) const { return 2*x; };
} twoTimes;
int main(int argc, char* argv[] )
{
cout << compose(twoTimes,twoTimes)(3) << endl;
return 0;
}
The error I get is:
In file included from full.h:14:0,
from lambda.h:38,
from operator.h:29,
from function.h:23,
from reuse.h:14,
from list.h:31,
from prelude.h:32,
from y.cxx:2:
smart.h: In instantiation of 'fcpp::FunctoidTraits<TwoTimes>':
prelude.h:142:74: instantiated from 'fcpp::impl::XCompose::Sig<TwoTimes, TwoTimes>'
full.h:94:53: instantiated from 'fcpp::Full2<fcpp::impl::XCompose>::Sig<TwoTimes, TwoTimes>'
y.cxx:18:46: instantiated from here
smart.h:103:7: error: no type named 'Type' in 'struct
fcpp::impl::NeededASmartFunctoidButInsteadGot<TwoTimes, false>'
In file included from y.cxx:2:0:
prelude.h: In instantiation of 'fcpp::impl::XCompose::Sig<TwoTimes, TwoTimes>':
full.h:94:53: instantiated from 'fcpp::Full2<fcpp::impl::XCompose>::Sig<TwoTimes, TwoTimes>'
y.cxx:18:46: instantiated from here
prelude.h:142:74: error: 'fcpp::FunctoidTraits<TwoTimes>::max_args' is not a valid
template argument for type 'int' because it is a non-constant expression
In file included from lambda.h:38:0,
from operator.h:29,
from function.h:23,
from reuse.h:14,
from list.h:31,
from prelude.h:32,
from y.cxx:2:
full.h: In instantiation of 'fcpp::Full2<fcpp::impl::XCompose>::Sig<TwoTimes, TwoTimes>':
y.cxx:18:46:
instantiated from here
full.h:94:53: error: no type named 'Arg1Type' in 'struct
fcpp::impl::XCompose::Sig<TwoTimes, TwoTimes>'
y.cxx: In function 'int main(int, char**)':
y.cxx:18:46: error: no match for call to '(fcpp::Compose) (TwoTimes&, TwoTimes&)'
Well .... the links you refer to are seven years old. In dog and compiler years, that is a good lifetime.
If you want functional programming with (current) C++ compilers, maybe some of the Boost libraries may be of interest?
If the answer is still needed to this, the struct TwoTimes needs to be wrapped to work with FC++. I have worked a lot with FC++ over several years. The best thing I can do is point to here on the C2 wiki where I have discussed this:
http://c2.com/cgi/wiki?FunctoidsInCpp
Any posting there I will see.