g++ : array bound is not an integer constant before ‘]’ token

Question

I'm having trouble with g++ producing this error code when I try to compile my code:

maze.h:16:29: error: array bound is not an integer constant before ‘]’ token bool canMove(int m[mazeSize][mazeSize], int r, int c);

Now, I have already done some research into this error and it seems to be causes by the array size not being known at compile time. I have tried making the array constant, but that ends up causing more errors later on as the array is reassigned later on in the code and produces this error:

maze.cpp: In member function ‘int Maze::startMazeGen()’: maze.cpp:185:15: error: assignment of read-only location ‘maze[i][j]’ maze[i][j] = 1; ^

I have also seen people mention that it would just be easier to work with vectors instead, but I'm also having issues with trying to repurpose the code to work with vectors instead of arrays.

Here's the rest of my code:

movement.h

#pragma once
#include <iostream>
#include <curses.h>
#ifndef MOVEMENT_H
#define MOVEMENT_H
class Movement
{
    public:
        static const int playerX = 2; // sets player starting position
        static const int playerY = 2;
};
#endif

movement.cpp

#include <iostream>
#include <curses.h>
#include <ctime>
#include "maze.h"
//#include "movement.h"

bool running = true;
int playerX = 2;
int playerY = 2;


//Maze::maze Maze::mazeGen;
//int Maze::mazeGen.Maze::maze::generateMaze::maze(int m[Maze::mazeSize]
[Maze::mazeSize], int r, int c);

// Detect Char input
// and move player in direction
void getUserInput()
{
    char userInput = getch();
    if (userInput == 'w') {
        int playerY2 = playerY - 1;
        if (Maze::maze[playerY2][playerX] == ' ') {
            Maze::maze[playerY][playerX] = ' ';
            playerY--;
            Maze::maze[playerY][playerX] = 'x';
    }
}
    if (userInput == 'a') {
        int playerX2 = playerX - 1;
        if (Maze::maze[playerY][playerX2] == ' ') {
            Maze::maze[playerY][playerX] = ' ';
            playerX--;
            Maze::maze[playerY][playerX] = 'x';
    }
}
    if (userInput == 's') {
        int playerY2 = playerY + 1;
        if (Maze::maze[playerY2][playerX] == ' ') {
            Maze::maze[playerY][playerX] = ' ';
            playerY++;
            Maze::maze[playerY][playerX] = 'x';
    }
}
    if (userInput == 'd') {
        int playerX2 = playerX + 1;
        if (Maze::maze[playerY][playerX2] == ' ') {
            Maze::maze[playerY][playerX] = ' ';
            playerX++;
            Maze::maze[playerY][playerX] = 'x';
        }
    }
}

// Main game update
// Runs through all functions required
void update()
{
    getUserInput();
    clear();
    Maze::generateMaze;
    refresh();
}


//
//
/*int main()
{
    // Initate nCurses display
    initscr();
    while (true) {
    update();
}
// End nCurses display
endwin();
return 0;
}*/

maze.h

#pragma once
// MAZE.h
#include <iostream>
#include <ctime>
#ifndef MAZE_H
#define MAZE_H
extern int r;
extern int c;
extern int mazeSize; //number can be changed to make some big sweaty mazes making it an even number makes it act a bit weird sometimes so its better to use an odd number
extern int maze[mazeSize][mazeSize];
class Maze
{
    public:
        int blockedSquare = 1;
        void move(int m[mazeSize][mazeSize], int &r, int &c);
        bool canMove(int m[mazeSize][mazeSize], int r, int c);
        void solve(int m[mazeSize][mazeSize], int &r, int &c);
        bool canSolve(int m[mazeSize][mazeSize], int r, int c);
        void generateMaze(int m[mazeSize][mazeSize], int r, int c);
        int findStart();
        void printMaze(int m[mazeSize][mazeSize]);
        int startMazeGen();
};
#endif

maze.cpp

#include <iostream>
#include <ctime>
#include <vector>
#include "maze.h"
bool foundExit = false;
int mazeSize = 31;
int maze[mazeSize][mazeSize] = { 0 };
void Maze::generateMaze(int const m[mazeSize][mazeSize], int r, int c)
{

    bool made = false;

    while (made == false)
    {
        if (c == mazeSize - 1)
            foundExit = true;


        if (canSolve(m, r, c))
        {
            solve(m, r, c);
        }
        else if (canMove(m, r, c))
        {
            m[r][c] = 2; //2 means you can't move from that square, setting any lower stops maze from being made
            move(m, r, c); //move to first open space that can be found
        }
        else
            made = true;

    }

}


void Maze::move(int m[mazeSize][mazeSize], int &r, int &c)
{
    if (m[r][c + 1] == 0)
        c++;
    else if (m[r + 1][c] == 0)
        r++;
    else if (m[r][c - 1] == 0)
        c--;
    else if (m[r - 1][c] == 0)
        r--;
    else
        generateMaze(maze, r, c); //if maze cant be solved it generates a new one so the player doesnt have something that is impossible to solve

}

bool Maze::canMove(int m[mazeSize][mazeSize], int r, int c) //if there is an adjacent zero space, return true
{
    if (m[r][c + 1] == 0)
        return true;
    else if (m[r + 1][c] == 0)
        return true;
    else if (m[r][c - 1] == 0)
        return true;
    else if (m[r - 1][c] == 0)
        return true;
    else
        return false;
}

void Maze::solve(int m[mazeSize][mazeSize], int &r, int &c) //solves maze through with dijkstras algorithmto ensure it can be solved
{
    bool foundSolution = false;

    while (foundSolution == false)
    {

        int direction = (1 + rand() % 4) * 3;

        switch (direction)
        {
        case 3:
            if (c + 1 <= mazeSize - 1 && m[r][c + 2] == blockedSquare && m[r - 1][c + 1] == blockedSquare && m[r + 1][c + 1] == blockedSquare && m[r][c + 1] == blockedSquare)
            {
                if (c == mazeSize - 2 && foundExit == true)
                    ; //do nothing
                else
                {
                    c++;
                    foundSolution = true;
                }
            }
            break;
        case 6:
            if (r + 1 <= mazeSize - 2 && m[r + 2][c] == blockedSquare && m[r + 1][c + 1] == blockedSquare && m[r + 1][c - 1] == blockedSquare && m[r + 1][c] == blockedSquare && c != 0 && c != mazeSize - 1)
            {
                r++;
                foundSolution = true;
            }
            break;
        case 9:
            if (c - 1 >= 0 && m[r][c - 2] == blockedSquare && m[r - 1][c - 1] == blockedSquare && m[r + 1][c - 1] == blockedSquare && m[r][c - 1] == blockedSquare && c - 1 != 0)
            {
                c--;
                foundSolution = true;
            }
            break;
        case 12:
            if (r - 1 >= 1 && m[r - 2][c] == blockedSquare && m[r - 1][c + 1] == blockedSquare && m[r - 1][c - 1] == blockedSquare && m[r - 1][c] == blockedSquare && c != 0 && c != mazeSize - 1)
            {
                r--;
                foundSolution = true;
            }
            break;
        }
    }

    m[r][c] = 0;
}



bool Maze::canSolve(int m[mazeSize][mazeSize], int r, int c) //if an adjacent square can be moved to, return true
{
    bool solvable = false;

    if (r <= mazeSize - 3 && m[r + 2][c] == blockedSquare && m[r + 1][c + 1] == blockedSquare && m[r + 1][c - 1] == blockedSquare && m[r + 1][c] == blockedSquare && c != 0 && c != mazeSize - 1) //if adjacent space can be moved to 
    {
        solvable = true;
    }
    else if (c <= mazeSize - 2 && m[r][c + 2] == blockedSquare && m[r - 1][c + 1] == blockedSquare && m[r + 1][c + 1] == blockedSquare && m[r][c + 1] == blockedSquare)
    {
        if (c == mazeSize - 2 && foundExit == true)
            ; //do nothing
        else
        {
            solvable = true;
        }
    }
    else if (r >= 2 && m[r - 2][c] == blockedSquare && m[r - 1][c + 1] == blockedSquare && m[r - 1][c - 1] == blockedSquare && m[r - 1][c] == blockedSquare && c != 0 && c != mazeSize - 1) //if not on extreme left or right
    {
        solvable = true;
    }
    else if (c >= 1 && m[r][c - 2] == blockedSquare && m[r - 1][c - 1] == blockedSquare && m[r + 1][c - 1] == blockedSquare && m[r][c - 1] == blockedSquare && c - 1 != 0)
    {
        solvable = true;
    }

    return solvable;
}

int Maze::findStart()
{
    return 1 + rand() % (mazeSize - 2);
}

void Maze::printMaze(int m[mazeSize][mazeSize])
{

    std::cout << std::endl;

    for (int i = 0; i < mazeSize; ++i) {
        for (int j = 0; j < mazeSize; ++j)
        {
            switch (m[i][j])
            {
            case 0:
                std::cout << "  ";
                break;
            case 1:
                std::cout << "▓▓";
                break;
            case 2:
                std::cout << "  ";
                break;
            case 3:
                std::cout << "  ";
                break;
            }
        }
        std::cout << std::endl;
    }
}

int Maze::startMazeGen()
{
    srand(time(0));

    for (int i = 0; i < mazeSize; ++i)
        for (int j = 0; j < mazeSize; ++j)
            maze[i][j] = 1;

    int r = findStart();
    //int r = 0;
    int c = 0;

    maze[r][c] = 0;

    generateMaze(maze, r, c);
    maze[r][c] = 2;
    printMaze(maze);
    std::cout << "Press enter to continue ...";
    std::cin.get();
}

The purpose of this code is to randomly generate a maze, solve it, and then print it to the screen if it can be solved. If the maze can't be solved, it keeps generating a new one until it can be solved.I aim to make this work with the movement code so that the user can navigate the maze.

Any help is appreciated on this issue. Thank you!

Answer 1

"Now, I have already done some research into this error and it seems to be causes by the array size not being known at compile time. I have tried making the array constant, but that ends up causing more errors later on as the array is reassigned later on in the code"

You're conflating two things here, the array and the array size.

The array size should be a a compile-time constant. Since you're assigning to the array, the array elements shouldn't be const at all.

const int arrSize = 3;
int arr[arrSize][arrSize];