https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80521
Bug ID: 80521
Summary: Wrong line reported in error for missing template
argument in friend class declaration.
Product: gcc
Version: 7.0.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: carlo at gcc dot gnu.org
Target Milestone: ---
Although similar to https://gcc.gnu.org/bugzilla/show_bug.cgi?id=8570 from
2002, I guess I'll report it again now, for version 7.0.1.
When compiling the following snippet:
-------------------------------
template<typename T>
struct RingBuffer {
private:
unsigned long m_capacity; // Number of objects of type T in the buffer.
union {
T* m_start; // Start of buffer.
char* m_storage;
};
T* m_head; // Next write position.
T* m_tail; // Next read position.
protected:
friend class ProducerAccess;
friend class ConsumerAccess;
public:
RingBuffer() : m_storage(nullptr), m_head(nullptr), m_tail(nullptr) { }
RingBuffer(int objects) : m_storage(nullptr), m_head(nullptr),
m_tail(nullptr) { allocate_(objects); }
~RingBuffer() { delete [] m_storage; }
private:
void allocate_(int objects)
{
m_capacity = objects * sizeof(T);
// Allocate storage aligned to at least 32 bytes.
//m_storage = new decltype(*m_storage) [m_capacity];
m_tail = m_head = m_start;
}
public:
void reallocate(int objects)
{
if (m_storage) delete [] m_storage;
allocate_(objects);
}
};
template<typename T>
struct ProducerAccess {
private:
RingBuffer<T>& m_buffer;
public:
ProducerAccess(RingBuffer<T>& buffer) : m_buffer(buffer) { }
~ProducerAccess() { }
};
template<typename T>
struct ConsumerAccess {
private:
RingBuffer<T>& m_buffer;
public:
ConsumerAccess(RingBuffer<T>& buffer) : m_buffer(buffer) { }
~ConsumerAccess() { }
};
int main()
{
// Construct an empty buffer.
RingBuffer<long> fifo_buffer;
// Allocate 100 std::function<void()> objects in it.
fifo_buffer.reallocate(100);
ProducerAccess<long> pa(fifo_buffer);
ConsumerAccess<long> ca(fifo_buffer);
}
------------------------------------------
You get an almost random location for where the problem is:
>g++-svn-7 -c bug.cxx
bug.cxx: In instantiation of ‘struct RingBuffer<long int>’:
bug.cxx:60:20: required from here
bug.cxx:10:6: error: template argument required for ‘class ProducerAccess’
T* m_tail; // Next read position.
^~~~~~
bug.cxx:10:6: error: template argument required for ‘class ConsumerAccess’
The real problem is here:
friend class ProducerAccess;
friend class ConsumerAccess;
Sorry for not minimizing the snippet further,
Carlo
