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dump() method doesn't work with a custom allocator #268
Description
Even if #161 isn't fixed, the dump() method still assumes the default allocator is used. Consider the following code:
nlohmann::basic_json<std::map, std::vector, StringWithMyAllocator, bool, int64_t, uint64_t, double, MyAllocator> j;
// add a string that is stored as std::string
j["name"] = "Niels";
// explicit conversion to string
StringWithMyAllocator s = j.dump(); // {\"happy\":true,\"pi\":3.141}This results in a compiler error:
'return': cannot convert from 'std::basic_string<char,std::char_traits,std::allocator>' to 'std::basic_string<char,std::char_traits,MyAllocator>'
The issue is due to the stringstream that is used without specifying the allocator for the stream. As a result, dump fails to compile due to the call to ss.str().
string_t dump(const int indent = -1) const
{
std::stringstream ss;
if (indent >= 0)
{
dump(ss, true, static_cast<unsigned int>(indent));
}
else
{
dump(ss, false, 0);
}
return ss.str();
}
Activity
nlohmann commentedon Jun 22, 2016
I actually never tried to use custom allocators in the string type. Your example shows that there is an apparent disconnect between the (in theory) adjustable
basic_json::string_tand the (implicitly assumed)std::stringreturned bystr().The quick "fix" would be to replace the return type of
dumpfrombasic_json::string_ttostd::string, because the type used to store strings inside a JSON value does not necessarily need to be the same type of a serialization.Alternatively, the user-defined allocator inside
basic_json::string_twould need to be passed down into the string stream.addressing the compiler error from #268
nlohmann commentedon Jun 22, 2016
I created a branch
feature/issue268(see a834338) which fixes the compilation error. Please let me know whether this works for you.nlohmann commentedon Jun 23, 2016
Thanks for checking back, and I am looking forward to see (the definitely needed) fixes!
michsco commentedon Jun 23, 2016
I created a fork of the project and a new branch feature/custom-allocator that contains initial changes. There are still a lot of assumptions built into the code using the default allocator for std::vector, std::map, and std::string.