I wanna pass NULL to the 4th param of the following function:
bool CCMenuItemToggle::initWithTarget(CCObject* target, SEL_MenuHandler selector, CCMenuItem* item, **va_list args**);
like this:
CCMenuItemToggle::initWithTarget(this, menu_selector(GOSound::toggleButtonCallback), NULL, NULL);
It's ok when I build it in XCode (clang3.1). But when I port the code to android ndk (g++4.7), it fails to compile:
no viable conversion from 'int' to 'va_list' (aka '__builtin_va_list')
How should I deal with it?
I assume your code will work if you just use an empty va_list
instead of NULL.
CCMenuItemToggle::initWithTarget( this, menu_selector(GOSound::toggleButtonCallback)
, NULL, va_list() );
Edit: Maybe this alternative solution works with both compilers.
va_list empty_va_list = va_list();
CCMenuItemToggle::initWithTarget( this, menu_selector(GOSound::toggleButtonCallback)
, NULL, empty_va_list );
I see this question was answered but it is not standard. the following code will through a runtime error in Visual Studios; however, it works fine with g++.
va_list empty_va_list;
CCMenuItemToggle::initWithTarget( this, menu_selector(GOSound::toggleButtonCallback), NULL, empty_va_list );
A better solution would be to create a couple helper functions that construct an empty va_list.
va_list CCMenuItemToggle::createEmptyVa_list()
{
return doCreateEmptyVa_list(0);
}
va_list CCMenuItemToggle::doCreateEmptyVa_list(int i,...)
{
va_list vl;
va_start(vl,i);
return vl;
}
make the doCreateEmptyVa_list private and then when you call your function call
CCMenuItemToggle::initWithTarget( this, menu_selector(GOSound::toggleButtonCallback), NULL, CreateEmptyVa_list() );
You cannot pass NULL
as the fourth argument of your function. That function requires a va_list
argument. NULL
in general case is not a valid initializer for a va_list
object. So, the answer to your question is: it is not possible.
How you should deal with it depends on what you are trying to do.
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