This is a follow up to my previous question about templates: Unable to use typedef definied in templated structure
When building the following piece of code, the compiler doesn't find the implementation of function, and outputs the the following error.
./test.cpp: In function ‘int main()’:
./test.cpp:30:13: error: no matching function for call to ‘function(BUFFER_T<128>::FRAME_DATA)’
30 | function(buffer.FrameData);
| ~~~~~~~~^~~~~~~~~~~~~~~~~~
./test.cpp:20:6: note: candidate: ‘template<unsigned int BufferSize> bool function(typename BUFFER_T<BufferSize>::FRAME_DATA&)’
20 | bool function(typename BUFFER_T<BufferSize>::FRAME_DATA& FrameBufferInput)
| ^~~~~~~~
./test.cpp:20:6: note: template argument deduction/substitution failed:
./test.cpp:30:13: note: couldn’t deduce template parameter ‘BufferSize’
30 | function(buffer.FrameData);
| ~~~~~~~~^~~~~~~~~~~~~~~~~~
How can I fix this error?
#include <stdint.h>
template<uint32_t BufferSize>
struct BUFFER_T
{
static constexpr uint32_t LENGTH_FRAME_NUMBER = 4u;
static constexpr uint32_t LENGTH_FRAME_OFFSET = 4u;
static constexpr uint32_t LENGTH_FRAME_CRC = 4u;
static constexpr uint32_t LENGTH_FRAME_DATA = BufferSize - LENGTH_FRAME_NUMBER - LENGTH_FRAME_OFFSET - LENGTH_FRAME_CRC;
typedef uint8_t FRAME_DATA [LENGTH_FRAME_DATA];
FRAME_DATA FrameData;
};
template<uint32_t BufferSize>
bool function(typename BUFFER_T<BufferSize>::FRAME_DATA& FrameBufferInput)
{
return true;
}
int main()
{
BUFFER_T<128u> buffer{};
function(buffer.FrameData);
return 0;
}
BufferSize can't be deduced because it's in a non-deduced context.
You could however make sure that you actually got an array of uint8_t as input:
template <uint32_t LENGTH_FRAME_DATA>
bool function(uint8_t(&FrameBufferInput)[LENGTH_FRAME_DATA]) {
// std::cout << LENGTH_FRAME_DATA << '\n';
return true;
}
It will however not make sure that the array belongs to a BUFFER_T instance and BufferSize and all the member constants are unavailable.
If you need access to the constants and want to make sure the buffer actually belongs to a BUFFER_T, you could simply take a BUFFER_T& instead:
template<uint32_t BufferSize>
bool function(BUFFER_T<BufferSize>& buff) {
auto& FrameBufferInput = buff.FrameData;
return true;
}
... and then call it with: function(buffer);.