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I have the following simple class:
class Source
{
public:
Source() = default;
Source(Source const&) = delete;
Source(Source&&) = default;
explicit Source(std::string const& fileName)
: inputStream(fileName), path_(fileName)
{}
~Source() = default;
auto path() const -> std::string
{
return this->path_;
}
std::ifstream inputStream;
private:
std::string path_;
};
auto main(int argc, char* argv[]) -> int
{
Source source(Source("test.txt"));
cout << source.path() << "\n";
return 0;
}
According to cppreference ifstream has a move constructor, but when I try to compile that with MinGW 4.7.2, I get the following error:
..\src\main.cpp:32:46: error: use of deleted function 'cy::Source::Source(cy::Source&&)' In file included from ..\src\main.cpp:10:0: source.hpp:28:5: note: 'cy::Source::Source(cy::Source&&)' is implicitly deleted because the default definition would be ill-formed: source.hpp:28:5: error: use of deleted function 'std::basic_ifstream::basic_ifstream(const std::basic_ifstream&)' c:\mingw\bin../lib/gcc/mingw32/4.7.2/include/c++/fstream:420:11: note: 'std::basic_ifstream::basic_ifstream(const std::basic_ifstream&)' is implicitly deleted because the default definition would be ill-formed: c:\mingw\bin../lib/gcc/mingw32/4.7.2/include/c++/fstream:420:11: error: use of deleted function 'std::basic_istream::basic_istream(const std::basic_istream&)'
Am I doing something wrong? Or the documentation of cppreference is inaccurate? Or GCC 4.7.2 has a bug?
255
Implicitly-defined move constructor For non-union class types (class and struct), the move constructor performs full member-wise move of the object's bases and non-static members, in their initialization order, using direct initialization with an xvalue argument.
If a copy constructor, copy-assignment operator, move constructor, move-assignment operator, or destructor is explicitly declared, then: No move constructor is automatically generated. No move-assignment operator is automatically generated.
A move constructor enables the resources owned by an rvalue object to be moved into an lvalue without copying. For more information about move semantics, see Rvalue Reference Declarator: &&. This topic builds upon the following C++ class, MemoryBlock , which manages a memory buffer.
In C++, the compiler creates a default constructor if we don't define our own constructor. In C++, compiler created default constructor has an empty body, i.e., it doesn't assign default values to data members. However, in Java default constructors assign default values.
It turns out that the standard library implementation of GCC has not implemented yet the move and swap operation for the stream classes. See here for detail about the current status of C++11 features in the gcc standard library.
Thanks Jesse Good for giving the information and link.
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