'islower'的重载无效

Question

I'm trying to develop the BattleShip game in C++ and I'm almost done. For that, I need my gameOver function working. My game is over when all the ships are sunk. Therefore, I'm trying to count how many lowercase chars I have in my string status (from Ship). When half of the chars are lowercase, the "ship" is destroyed and I'm ready to use my gameOver function.

But somehow my count_if isn't working and I don't know why.

Here you go:

#include <algorithm>

bool Ship::isDestroyed() const{ 
    //This counts those chars that satisfy islower:
    int lowercase = count_if (status.begin(), status.end(), islower); 
    return ( lowercase <= (status.length/2) ) ? true : false;
}

bool Board::gameOver() {
    bool is_the_game_over = true;
    for(int i = 0 ; i < ships.size() ; i++){
        if( ships[i].isDestroyed() == false ) {
            //There is at least one ship that is not destroyed.
            is_the_game_over = false ;
            break;
        }
    }
    return is_the_game_over;
}

What am I doing wrong?

Answer 1

Unfortunately, the standard library has more than one overload of islower (a function from the C library, and a function template from the localisation library), so you can't simply name the function unless you're calling it.

You could convert it to the right function type:

static_cast<int (*)(int)>(islower)

or hope that your implementation dumps the C library into the global namespace as well as std :

::islower      // not guaranteed to work

or wrap it in a lambda

[](int c){return islower(c);}

Answer 2

Try to change the algorithm call the following way

int lowercase = count_if (status.begin(), status.end(), ::islower); 
                                                        ^^^

The compilers are allowed to place standard C functions in the global namespace.

Otherwise use a lambda expression as for example

int lowercase = count_if (status.begin(), status.end(), 
                          []( char c ) return islower( c ); } );