I am a beginner in C , so I'm sure the error is from my misunderstanding of pointers.
I was making a Poker game, where card is a struct with the suit and the value, and each player's hand is filled with cards, and the middle is filled with cards. I passed references of the arrays to a function by reference, but I think something is wrong with how I set up the pointers to the arrays.
Here is a simplified version of my code:
#include <iostream>
enum suit {hearts, diamonds, spades, clubs};
enum value {two, three, four, five, six, seven, eight, nine, ten, jack, queen, king, ace};
struct card
{
value v;
suit s;
};
static const int num_players = 4;
void get_winner(const card ** hands[num_players][2], const card * mid_cards[5])
{
for (int i = 0; i < 5; i ) {
std::cout << "Middle card " << i 1 << ": " << * mid_cards[i][0] << ", " << * mid_cards[i][1] << "\n";
}
for (int i = 0; i < num_players; i ) {
std::cout << "Player " << i 1 << "hand: " << * hands[i][0] << ", " << * hands[i][1] << "\n";
}
}
int main()
{
card hands[num_players][2];
card mid_cards[5];
// fill hands and mid_cards with card structs
hands[0][0] = card {jack, hearts};
hands[0][1] = card {nine, spades};
hands[1][0] = card {ace, clubs};
hands[1][1] = card {ace, hearts};
hands[2][0] = card {three, diamonds};
hands[2][1] = card {seven, spades};
hands[3][0] = card {eight, diamonds};
hands[3][1] = card {nine, clubs};
mid_cards[0] = card {five, clubs};
mid_cards[1] = card {king, hearts};
mid_cards[2] = card {queen, spades};
mid_cards[3] = card {two, clubs};
mid_cards[4] = card {ace, hearts};
get_winner(&hands, &mid_cards);
}
Here are the error messages:
main.cpp:17:51: error: indirection requires pointer operand
('const card' invalid)
...<< "Middle card " << i 1 << ": " << * mid_cards[i][0] << ", " << * mid...
^ ~~~~~~~~~~~~~~~
main.cpp:17:80: error: indirection requires pointer operand
('const card' invalid)
...i 1 << ": " << * mid_cards[i][0] << ", " << * mid_cards[i][1] << "\n";
^ ~~~~~~~~~~~~~~~
main.cpp:42:2: error: no matching function for call to 'get_winner'
get_winner(&hands, &mid_cards);
^~~~~~~~~~
main.cpp:14:6: note: candidate function not viable: no known conversion from
'card (*)[4][2]' to 'const card **(*)[2]' for 1st argument
void get_winner(const card ** hands[num_players][2], const card * mid_cards[5])
^
3 errors generated.
CodePudding user response：
In your function's parameters, you are using the wrong syntax to accept the arrays by pointer. And, you are declaring the wrong element type for the arrays (you claim card* pointers, but the arrays actual hold card objects instead). And, your function is treating the mid_cards parameter like it is a pointer to a 2-dimentional array when the actual array in main() is 1-dimensional instead.
Also, you do not have an operator<< defined for your card struct, but you are trying to print card values to cout.
Try this instead:
#include <iostream>
enum suit {hearts, diamonds, spades, clubs};
enum value {two, three, four, five, six, seven, eight, nine, ten, jack, queen, king, ace};
struct card
{
value v;
suit s;
};
static const int num_players = 4;
static const char* suits[] = {"Hearts", "Diamonds", "Spades", "Clubs"};
static const char* values[] = {"2", "3", "4", "5", "6", "7", "8", "9", "10", "Jack", "Queen", "King", "Ace"};
std::ostream& operator<<(std::ostream &out, const card &c)
{
out << values[c.v] << " of " << suits[c.s];
return out;
}
void get_winner(const card (*hands)[num_players][2], const card (*mid_cards)[5])
{
for (int i = 0; i < 5; i ) {
std::cout << "Middle card " << i 1 << ": " << (*mid_cards)[i] << "\n";
}
for (int i = 0; i < num_players; i ) {
std::cout << "Player " << i 1 << "hand: " << (*hands)[i][0] << ", " << (*hands)[i][1] << "\n";
}
}
int main()
{
card hands[num_players][2];
card mid_cards[5];
// fill hands and mid_cards with card structs
hands[0][0] = card {jack, hearts};
hands[0][1] = card {nine, spades};
hands[1][0] = card {ace, clubs};
hands[1][1] = card {ace, hearts};
hands[2][0] = card {three, diamonds};
hands[2][1] = card {seven, spades};
hands[3][0] = card {eight, diamonds};
hands[3][1] = card {nine, clubs};
mid_cards[0] = card {five, clubs};
mid_cards[1] = card {king, hearts};
mid_cards[2] = card {queen, spades};
mid_cards[3] = card {two, clubs};
mid_cards[4] = card {ace, hearts};
get_winner(&hands, &mid_cards);
}
Alternatively, pass the arrays by reference instead of pointer, eg:
#include <iostream>
enum suit {hearts, diamonds, spades, clubs};
enum value {two, three, four, five, six, seven, eight, nine, ten, jack, queen, king, ace};
struct card
{
value v;
suit s;
};
static const int num_players = 4;
static const char* suits[] = {"Hearts", "Diamonds", "Spades", "Clubs"};
static const char* values[] = {"2", "3", "4", "5", "6", "7", "8", "9", "10", "Jack", "Queen", "King", "Ace"};
std::ostream& operator<<(std::ostream &out, const card &c)
{
out << values[c.v] << " of " << suits[c.s];
return out;
}
void get_winner(const card (&hands)[num_players][2], const card (&mid_cards)[5])
{
for (int i = 0; i < 5; i ) {
std::cout << "Middle card " << i 1 << ": " << mid_cards[i] << "\n";
}
for (int i = 0; i < num_players; i ) {
std::cout << "Player " << i 1 << "hand: " << hands[i][0] << ", " << hands[i][1] << "\n";
}
}
int main()
{
card hands[num_players][2];
card mid_cards[5];
// fill hands and mid_cards with card structs
hands[0][0] = card {jack, hearts};
hands[0][1] = card {nine, spades};
hands[1][0] = card {ace, clubs};
hands[1][1] = card {ace, hearts};
hands[2][0] = card {three, diamonds};
hands[2][1] = card {seven, spades};
hands[3][0] = card {eight, diamonds};
hands[3][1] = card {nine, clubs};
mid_cards[0] = card {five, clubs};
mid_cards[1] = card {king, hearts};
mid_cards[2] = card {queen, spades};
mid_cards[3] = card {two, clubs};
mid_cards[4] = card {ace, hearts};
get_winner(hands, mid_cards);
}