When compiling my code (you will see why this big and not an MRE snippet later)
template<typename Elem>
class base_stream
{
protected:
array_list<Elem>* buffer_ = nullptr; // array_list is my class, it works
public:
virtual void open() = 0;
virtual void close() = 0;
};
template<typename Elem>
class base_input_stream : public base_stream<Elem>
{
public:
void open() override
{
this->buffer_ = new array_list<Elem>;
}
void close() override
{
this->buffer_ = nullptr;
}
Elem* read_until(Elem terminator)
{
Elem e;
while((e = read()) != terminator) this->buffer_->add(e);
return this->buffer_->as_array();
}
virtual Elem read();
};
class input_stream : public base_input_stream<char>
{
private:
FILE* file_;
public:
input_stream(FILE* f)
{
file(f);
open();
}
input_stream() { open(); }
~input_stream()
{
close();
delete buffer_;
}
char* read_line()
{
return this->read_until('\n');
// the problem is here, when I remove read_line, everything works.
}
char read() override
{
return fgetc(file_);
}
void file(FILE* f)
{
file_ = f;
}
};
and the cpp file
msl::input_stream is(stdin);
msl::stdos.write("Hello, ");
msl::stdos.write(is.read_line());
(please don't judge me for what I'm doing...)
this error appears:
Undefined symbols for architecture x86_64:
"msl::base_input_stream<char>::read()", referenced from:
vtable for msl::base_input_stream<char> in msl-test-9638bd.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
but (strangely) this works:
#include <iostream>
template<typename E>
class X
{
};
template<typename E>
class Y : public X<E>
{
public:
void doStuff(E foo)
{
std::cout << foo << std::endl;
}
};
class Z : public Y<char>
{
public:
void hmm() {
doStuff('h');
// or Y<char>::doStuff('h');
// or this->doStuff('h');
}
};
Z hmm = Z();
and compiles without any errors. (the output is as expected h)
What is the problem here. The error is strange because other methods work and only read_line doesn't
