I'm trying to call this method
#define SIZE 16
void DoSomething(char(&value)[SIZE])
{
}
From this method:
void BeforeDoingSomething(char* value, int len)
{
if (len == SIZE)
{
DoSomething(value);
}
}
Attempting to do this gives me this error:
a reference of type "char (&)[16]" (not const-qualified) cannot be initialized with a value of type "char *"
Any tips for how to get the compiler to accept value passed in the function BeforeDoingSomething?
As the error explains, you cannot initialize a reference to an array using a pointer.
If and only if you can prove that value does in fact point to (first element of) an array of appropriate type, then what you can do is explicitly reinterpret the pointer, and indirect it:
DoSomething(*std::launder(reinterpret_cast<char(*)[SIZE]>(value)));
std::launder here because of the strict aliasing rule?
reinterpret_cast doesn't do that for you, as the pointers are not interconvertible).You can do it like this, but only in the case if there is a char[16] at the address where value points:
DoSomething(*std::launder(reinterpret_cast<char (*)[16]>(value)));
It is the same case as the first example here.
The use of std::launder as suggested by @user2079303 is a good option if you are sure that value does indeed point to an array of the right size as mentioned in their answer.
Yet another approach: since SIZE is fairly small in this case, it may be safer/simpler to create a temporary copy of value and pass it to DoSomething(). But it all depends on what DoSomething() is actually doing (for example, does it modify the array passed to it). For example:
#include <iostream>
#include <vector>
#include <string>
constexpr int SIZE = 16 ;
void DoSomething(char (&value)[SIZE])
{
std::cout << "Do it!" << std::endl ;
}
void BeforeDoingSomething(char* value, int len)
{
if (len == SIZE)
{
char tmp_array[SIZE] ;
std::copy(value, value + len, tmp_array) ;
DoSomething(tmp_array);
} else {
std::cout << "Length: " << len << std::endl ;
}
}
int main()
{
std::string foo (SIZE, '-') ;
BeforeDoingSomething(foo.data(), foo.size()) ;
std::vector<char> bar (SIZE) ;
BeforeDoingSomething(bar.data(), bar.size()) ;
std::string qux ;
BeforeDoingSomething(qux.data(), qux.size()) ;
return 0 ;
}
Try it online here.
valuepoints to the start of achar[SIZE]? You might be able toreinterpret_castbut I'm not certain. I wouldn't recommend in any case.DoSomethingalways need an array of lengthSIZE? Why can'tBeforeDoingSomethingalways use an array of lengthSIZEinstead of a pointer and length?DoSomethingwrote it this way, and when a call is made into my DLL it's in the form inside ofBeforeDoingSomething. I'm not sure how to even go about enforcing something likechar(&value)[SIZE]when it comes to people calling into the DLL (which the callers will not be C++)