C++ Error 1 error C2664 passing array pointers

Question

I don't understand how fix this problem, tried many things but no solution. Help on it would be much appreciated. Thanks.

Error 1 error C2664: 'void showAllBuses(const Bus *[],int)' : cannot convert argument 1 from 'Bus **' to 'const Bus *[]'

void showAllBuses(const Bus* pBuses[], int numBus) {
    for (int i = 0; i < numBus; i++) {
        cout << "Bus no ." << numBus << " details: " << endl;
        cout << "Number: " << pBuses[i]->getNumber() << endl;
        cout << "Driver name: " << pBuses[i]->getDriver().getName() << endl;
        cout << "Driver experience(years): " << pBuses[i]->getDriver().getYearsDriving() << endl;
    }
}

void listBusesWithYearsDriving(const Bus* pBuses[], int numBus, int drivingYears) {
    for (int i = 0; i < numBus; i++) {
        if (pBuses[i]->getDriver().getYearsDriving() >= drivingYears) {
            cout << "Bus number: " << pBuses[i]->getNumber() << endl;
            cout << "Driver name: " << pBuses[i]->getDriver().getName() << endl;
            cout << "Driver experience: " << pBuses[i]->getDriver().getYearsDriving() << endl;
        }
    }
}

void removeDriver(Bus* pBuses[], int busPos) {
    pBuses[busPos]->removeDriver();
}

void main() {
    const int ASIZE = 4;
    int drivingYears = 0;
    Bus* buses = new Bus[ASIZE];
    for (int i = 0; i < ASIZE; i++) {
        addNewBus(&buses[i]);
        cout << "Bus " << i << ": " << &buses[i] << endl;
    }
    showAllBuses(&buses, ASIZE);
    cout << "Please enter a minimum years of experience to look for: " << endl;
    cin >> drivingYears;
    listBusesWithYearsDriving(&buses, ASIZE, drivingYears);
    removeDriver(&buses, 0);
    showAllBuses(&buses, ASIZE);
    delete[] buses;
    buses = nullptr;
    cout << "\n\n";
    system("pause");
}

Angew is no longer proud of SO · Accepted Answer · 2015-04-20 16:46:26Z

2

For any type T, T* can be implicitly converted to const T*, but T** cannot be implicitly converted to const T**. Allowing this would make it possible to violate constness⁽¹⁾.

A T ** can be converted to const T* const *, though. Since your function does not modify the array in any way, you can simply change its parameter like that:

void showAllBuses(const Bus* const * pBuses, int numBus) {

Bear in mind that in a function parameter declaration, * and the outermost [] are synonyms.

⁽¹⁾ Here's the code:

const int C = 42;
int I = -42;
int *p = &I;
int *pp = &p;
const int **cp = pp;  // error here, but if it was allowed:
*cp = &C;  // no problem, *cp is `const int *`, but it's also `p`!
*p = 0;  // p is &C!

answered Apr 20, 2015 at 16:46

Angew is no longer proud of SO

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