问题
Using gcc version 4.8.2:
I'm running into an issue where the const qualifier on my parameters is disappearing when I compile my code. Here is an example:
main.cc:
#include <iostream>
class Base
{
public:
virtual int getSum( const int number ) = 0;
};
class Derived : public Base
{
public:
Derived( const int& num )
: _myNumber( num )
{}
virtual int getSum( const int number )
{
return _myNumber + number;
}
private:
int _myNumber;
};
int main( int argc, const char* argv[] )
{
Base *b = new Derived( 2 );
std::cout << b->getSum( 3 ) << "\n";
}
Compiled like so:
g++ main.cc -o const_test
When I run nm:
nm const_test | c++filt | grep getSum
I get the following output:
0000000000400b60 W Derived::getSum(int)
Why does the const disappear from my function when it compiles?
回答1:
Your function signature
virtual int getSum(const int number) = 0;
is actually exactly equivalent to
virtual int getSum(int number) = 0;
const
has no effect on the function signature declaration for parameters passed by value.
The only effect is, that you can't change the parameter instance on the stack inside of a potential definition of this method. It's in fact sufficient to put it only there, to prevent changing the parameter's instance in the function body.
来源:https://stackoverflow.com/questions/24290732/const-qualifier-disappears-from-pure-virtual-function