Error with calling a private constructor on macos - macos

Question

I am trying to port some C++ code that encodes the given data into base64 to macos. This is the a code sample from the same source which compiles and executes on godbolt but not on my mac:
#include <vector>
#include <string>
#include <boost/archive/iterators/base64_from_binary.hpp>
#include <boost/archive/iterators/transform_width.hpp>
#include <boost/archive/iterators/insert_linebreaks.hpp>
using namespace boost::archive::iterators;
struct Encode
{
/// Sets the contents of an std::string to be used
/// as the input for the encoding operation.
/// \param a_Data The string to encode.
Encode(const std::string& a_Data);
/// Evaluates the expression and performs the base64 encoding.
/// \returns Base64 encoded string.
operator std::string() const;
private:
std::string Evaluate() const;
const char * m_Data;
size_t m_Size;
bool m_LineBreaks;
};
Encode::Encode(const std::string& a_Data)
: m_Data(a_Data.c_str())
, m_Size(a_Data.size())
, m_LineBreaks(false)
{
}
std::string Encode::Evaluate() const
{
typedef base64_from_binary<
transform_width<std::string::const_iterator,6,8>
> iterator;
typedef insert_linebreaks<iterator, 72> linebreak_iterator;
std::string base64;
if (m_LineBreaks) {
base64.assign(
linebreak_iterator(m_Data),
linebreak_iterator(m_Data + m_Size));
}
else {
base64.assign(
iterator(m_Data),
iterator(m_Data + m_Size));
}
return base64;
}
Encode::operator std::string() const
{
return Evaluate();
}
int main()
{
const std::string str64 = Encode("Hello World");
return 0;
}
I am compiling using g++:
Configured with: --prefix=/Library/Developer/CommandLineTools/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 10.0.0 (clang-1000.10.44.2)
Target: x86_64-apple-darwin17.7.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin
However, there is the following error on line iterator(m_Data),:
boost/archive/iterators/transform_width.hpp:112:17: error: calling a private constructor of class 'std::__1::__wrap_iter<const char *>'
super_t(Base(static_cast< T >(start))),
^
<build_path>/boost/archive/iterators/base64_from_binary.hpp:91:13: note: in instantiation of function template specialization 'boost::archive::iterators::transform_width<std::__1::__wrap_iter<const char *>, 6, 8,
char>::transform_width<const char *>' requested here
Base(static_cast< T >(start)),
^
<src_path>/utilsBase64.cc:105:13: note: in instantiation of function template specialization 'boost::archive::iterators::base64_from_binary<boost::archive::iterators::transform_width<std::__1::__wrap_iter<const char *>, 6, 8, char>, char>::base64_from_binary<const
char *>' requested here
iterator(m_Data),
^
/Library/Developer/CommandLineTools/usr/include/c++/v1/iterator:1420:31: note: declared private here
_LIBCPP_INLINE_VISIBILITY __wrap_iter(iterator_type __x) _NOEXCEPT_DEBUG : __i(__x) {}
^
I have attempted to use clang++ and tried setting -stdlib=libc++ or stdlib=libstdc++ with a similar result. All examples of using the base64_from_binary shown in the code are similar to the given code sample.
One additional detail about m_Data, it is a member variable declared as: const char * m_Data;
Could someone please explain how this can be resolved?

Answer 1

Modifying the code to the following helped fix the issue:
std::string Encode::Evaluate() const
{
typedef base64_from_binary<
transform_width<std::string::const_iterator,6,8>
> iterator;
typedef insert_linebreaks<iterator, 72> linebreak_iterator;
std::string data(m_Data, m_Size);
std::string base64;
if (m_LineBreaks) {
base64.assign(
linebreak_iterator(data.begin()),
linebreak_iterator(data.end()));
}
else {
base64.assign(
iterator(data.begin()),
iterator(data.end()));
}
return base64;
}