C++ tic tac toe game only wins with one combination - c++

Question

I want the program to print "You win" when any of the instances in the champion() function are given. It only shows a winner when "123" is inputted. Whenever three X's are displayed anywhere else the program continues. For instance if three X's are given diagonally the program will still continue. Novice programmer so any criticism is greatly appreciated.
class TicTacToe {
private:
char map[GRID_SIZE][GRID_SIZE];
public:
void computers_turn() {
while (true) {
int choice = (rand() % 9) + 1;
int row = choice / 3;
int col = choice % 3;
char grid_position = map[row][col];
if (grid_position == 'X' || grid_position == 'O') {
std::cout << "Space taken. Try again" << std::endl;
} else {
map[row][col] = (char)'O';
break;
}
}
}
void champion() {
const char* possiblities[8] = {"123", "456", "789", "147",
"258", "369", "159", "753"};
for (int i = 0; i < 8; i++) {
char previous_pos = '0';
bool winner = true;
const char* possible_moves = possiblities[i];
for (int index = 0; index < GRID_SIZE; index++) {
char character = possible_moves[i];
int entered_num = character - '0';
int grid_space = entered_num - '1';
int row = index / GRID_SIZE;
int col = index % GRID_SIZE;
char grid_coordinate = map[row][col];
if (previous_pos == '0') {
previous_pos = grid_coordinate;
} else if (previous_pos == grid_coordinate) {
continue;
} else {
winner = false;
break;
}
}
if (winner) {
puts("You win");
exit(0);
break;
}
}
}
void playgame() {
std::string input;
while (true) {
std::cout << "Go player one" << std::endl;
getline(std::cin, input);
if (input != " ") {
char entered = input.c_str()[0];
if (entered >= '1' && entered <= '9') {
int entered_num = entered - '0';
int index = entered_num - 1;
int row = index / 3;
int col = index % 3;
char grid_position = map[row][col];
if (grid_position == 'X' || grid_position == 'O') {
std::cout << "Space taken. Try again" << std::endl;
} else {
map[row][col] = (char)'X';
break;
}
} else {
std::cout << "Only numbers 1 - 9" << std::endl;
}
} else {
std::cout << "Have to enter something, try again" << std::endl;
}
}
}
void generateGrid() {
int number = 1;
for (int x = 0; x < GRID_SIZE; x++) {
for (int y = 0; y < GRID_SIZE; y++) {
map[x][y] = std::to_string(number).c_str()[0];
number += 1;
}
}
}
void tictacToeMap() {
std::cout << std::endl;
for (int x = 0; x < GRID_SIZE; x++) {
for (int y = 0; y < GRID_SIZE; y++) {
std::printf(" %c ", map[x][y]);
}
std::cout << std::endl;
}
}
TicTacToe() {
generateGrid();
while (true) {
champion();
tictacToeMap();
playgame();
computers_turn();
}
}
};
int main() {
TicTacToe ticTacToe;
return 0;
}