Re: newbie: C++ static initializer (constructor vs bool)
andrew_nuss@yahoo.com wrote:
Hi,
This is obviously a newbie question. I know that constructors for
static class instances are invoked in different modules in
unpredictable order. My question is whether this is true of static
boolean variables as well. For example, in the following code, I'm
wondering if the Digest::Hash() function can be called safely from
other initializers, which would be true if the "inited" boolean is
guaranteed to be set to its initial value before any static
constructors are invoked in any modules. If the same unpredictability
of static initializer order applies to booleans then this code is
unsafe. Which is the case?
Your suspicion that booleans (and other built-in types) are initialised
first is correct. In fact, any global or static POD member is just laid
out in the executable you're loading directly, and no real
initialisation is happening. That's the reason why you specify a value
at definition for those types (as your comment says you did), but not
for non-PODs.
So you're code is safe in that regard. Some unrelated comments:
array = reinterpret_cast<int*>(malloc(sizeof(int)*RANGE));
1. Use new rather than malloc (malloc is C)
2. Use static_cast for this kind of cast. Use const_cast and
dynamic_cast in other cases. Never use the legacy C-style cast you used
below, and also never use reinterpret_cast unless you know exactly what
you're doing.
So better is:
array = new int[RANGE];
Even better is to use a container so you don't deal with memory
management yourself.
Then, since these are not built-in types, you have the problem of
initialisation order again. Thus, I'd also suggest using function-scope
statics, as these are guaranteed to be initialised in order of first use:
struct Digest
{
Digest()
{
// init mArray here
}
int Hash(int v)
{
return mArray[v];
}
std::vector< int > mArray;
};
Digest const& getGlobalDigest()
{
static Digest singleton;
return singleton;
}
int main()
{
int x = getGlobalDigest().Hash(42);
}
(untested)
Jens
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