what is the operator be overloading here : String8::operator const char*() const
I know it is used to get the containing c string ,similar to std::string.c_str().
But how should I use the operator?
//android/frameworks/base/include/utils/String8.h
458 inline String8::operator const cha开发者_StackOverflowr*() const
459 {
460 return mString;
461 }
This is a user-defined conversion, which allows you to convert from a user-defined type to another type.
You could do stuff like this, by using it to get a const char*
from a String8
object.
String8 str = "Hello";
const char *cptr = str; // gets const char* from str
std::strlen(str); // std::strlen expects a const char*
It's not so much about how you use it (explicitly), as letting it be used implicitly. Where you'd use .c_str()
for a std::string
, just leave off the .c_str()
. Of course the problem is ambiguity: std::string
lacks such an operator for a good reason, and you may occasionally find yourself having to explicitly invoke the operator so the compiler knows which behaviour to use.
EDIT: example in response to UncleBens' comment:
#include <iostream>
struct X
{
operator const char*() { return "hello world\n"; }
};
int main()
{
X x;
std::cout << x.operator const char*();
}
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