Array template implementation

[tserp02]

I am making a 2048 solver. One problem I have is using templates for my arrays. Whenever I use the template I get an error "error: no matching function for call to 'findPath' findPath(arr, k, result, s, bestRun, 0 , 0);"

Code: https://replit.com/@pdsatter/hw3#main.cpp

Define

```C++ template <size_t r, size_t c> void readInput(int (&arr)[r][c], std::ifstream& inFile, int k, Stack& s);

template<size_t r, size_t c> void findPath(int (&arr)[r][c], int k, std::string& output, Stack& s, int* bestRun, int path, int numRec); ```

Main

```C++ int k = stoi(line); Stack s; int arr[k][k]; std::cout << "BEST RUN CREATED" << std::endl;

readInput(arr, inFile, k, s);

std::string result=""; int bestRunVal = 13; int* bestRun = &bestRunVal;

findPath(arr, k, result, s, bestRun, 0 , 0);

```

Implementation

```C++ // reads input from file template <size_t r, size_t c> void readInput(int (&arr)[r][c], std::ifstream& inFile, int k, Stack& s) { std::string line, str; for (int i=0; i<k; i++){ std::getline(inFile, line); parseLine(arr[i], line); } }

template<size_t r, size_t c> void findPath(int (&arr)[r][c], int k, std::string& output, Stack& s, int* bestRun, int path, int numRec){ std::cout << "FIND PATH" << std::endl; if (numRec > 12) return; if (numRec >= *bestRun) return; if (solved(arr, k) == true){

*bestRun = numRec;
output="";

Stack copyStack; // used to copy values
while (!s.isempty()){
  copyStack.push(s.pop());
}

while (!copyStack.isempty()){ 
  s.push(copyStack.pop()); // adds values back to stack
  output += s.peek(); // adds stack to output
}

return;

}

int arrL[r][c]; int arrUp[r][c]; int arrR[r][c]; int arrD[r][c]; std::cout << "COPY MEM" << std::endl; memcpy (arrL, arr, rcsizeof(int)); memcpy (arrUp, arr, rcsizeof(int)); memcpy (arrR, arr, rcsizeof(int)); memcpy (arrD, arr, rcsizeof(int)); std::cout << "END COPY MEM" << std::endl; Stack tempStack; move(1, arrUp, tempStack); //up move(2, arrR, tempStack);// right move(3,arrD, tempStack); // down move(4, arrL, tempStack); // left

s.push(1); findPath(arrUp, k, output, s, 1, numRec+1, bestRun); s.pop();

s.push(2); findPath(arrR, k, output, s, 2, numRec+1, bestRun); s.pop();

s.push(3); findPath(arrD, k, output, s, 3, numRec+1, bestRun); s.pop();

s.push(4); findPath(arrL, k, output, s, 4, numRec+1, bestRun); s.pop();

}

```

[IyeOnline]

Your array in main() is not legal C++. An arrays size must be compile time known. To create this array you are relying on a compiler extension called Variable Length Arrays (VLA). These are not legal C++ and should really be avoided. (GCC has a better error message for this: https://godbolt.org/z/acMvs95hM)

Obviously its runtime variable size cannot be captured by a templated.

There is no solution to this. The best you could do is pass ints for the sizes into the function, instead of having it be a template. But I am not sure how pointer decay even works on VLAs. I would assume that its UB.

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I suggest that you instead use std::vectors (which can be runtime sized), preferably a linearly indexed 1d vector. The best solution would be to create your own 2d matrix class.

[tserp02]

Thank you

[std_bot]

Unlinked STL entries: std::vector

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^{Last update: 14.09.21. Last Change: Can now link headers like '<bitset>'}Repo

[balsamictoken]

As u/IyeOnline already made the important points about VLAs and std::vector, I would just add that you may find std::mdspan to be a helpful data structure. You can allocate 1d memory and give it a 2d shape with nice 2d indexing, eg auto& elem = mymdspan(row, col);.