Unresolved external symbol when using std::wstring - c++

Question

I declared the the following class:
#pragma once
#include <stdio.h>
#include <vector>
#include <string>
namespace util
{
class FileReader
{
public:
FileReader();
~FileReader();
bool open(const std::wstring& name);
void close();
bool read(std::vector<char>& buf, __int64 startFrom, int size);
__int64 size() const;
private:
FILE* m_file;
std::wstring m_name;
__int64 m_size;
};
}
And its implementation:
#include "FileReader.hpp"
namespace util
{
bool FileReader::open(const std::wstring& name)
{
if (!name.empty() && (m_name != name))
{
close();
if (_wfopen_s(&m_file, name.c_str(), L"rb") == 0)
{
m_name = name;
// Get the file size
_fseeki64(m_file, 0, SEEK_END);
m_size = _ftelli64(m_file);
rewind(m_file);
}
else
{
m_file = NULL;
}
}
return (m_file != NULL);
}
// ....
}
in a seperate library and use it like this:
FileTransfer.cpp
#include <util/FileReader.hpp>
// .....
if (!m_fileReader.open(m_localFileName)) // std::wstring m_localFileName;
{
::MessageBoxA(NULL, "Failed to open file", "Error", MB_ICONERROR);
stopFileTransmission();
return;
}
in another project. Both projects compile successfully, but the FileTransfer.obj fails to link:
Error 2 error LNK2019: unresolved external symbol "public: bool
__thiscall util::FileReader::open(class std::basic_string,class
std::allocator > const &)"
(?open#FileReader#util##QAE_NABV?$basic_string#GU?$char_traits#G#std##V?$allocator#G#2##std###Z)
referenced in function
__catch$?onRequestDirClicked#FileTransferWindow##AAEXXZ$0 C:\Users\x\Documents\dev\Server\FileTransfer.obj Server
I remember it was working when I used std::string, so I assume it has something todo with std::wstring.
Any idea what could be the issue?

Answer 1

It seems, the problem was that the two projects had different values for the setting
Treat wchar_t as built-in type
Setting it to No (/Zc:wchar_t-) for both projects, solved the linker error. I still don't really know what the consequences will be though.

Answer 2

try using extern "C" to declare the open function.