C ++ passing using dynamic size of 2D array

Question

I am trying to figure out how to pass a 2D array that is dynamically built for a function. I know that the number of columns should be specified, but it depends on user input.

Are there any workarounds?

Example:

// Some function void function(matrix[i][j]) { // do stuff } // Main function int N; cout << "Size: "; cin >> N; int matrix[N][N]; for (int i=0;i<N;i++) { // for (int j=0;j<N;j++) { cin >> matrix[N][N]; } } sort(matrix); 

You get the idea :)

Answer 1

If you are in C ++, reasonable options are:

• use boost::multi_array (recommended) or
• create your own class of 2D arrays. Well, you don’t have to, but encapsulating 2D array logic in a class is useful and makes the code clean.

Manual indexing of a 2D array will look like this:

 void func(int* arrayData, int arrayWidth) { // element (x,y) is under arrayData[x + y*arrayWidth] } 

But seriously, either wrap it in a class, or enjoy the fact that Boost already has this class, ready for you. Indexing this manually is tedious and makes the code more unclean and error prone.

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change

http://gcc.gnu.org/onlinedocs/gcc/Variable-Length.html says that C99 has another solution for you:

 void func(int len, int array[len][len]) { // notice how the first parameter is used in the definition of second parameter } 

Should also work in C ++ compilers, but I have never used this approach.

Answer 2

In C ++, the compiler can determine the size, since it is part of the type. However, it will not work with matrices with dynamic size.

 template<size_t N, size_t M> void function(int (&matrix)[N][M]) { // do stuff } 

EDIT: only in GCC, which is necessary for your code defining an array, can you pass arrays of variable length directly:

 void func(int N, int matrix[N][N]) { //do stuff } 

See gcc documentation

Answer 3

 /*******************************************************\ * * * I am not claiming to be an expert, but I think I know * * a solution to this one. Try using a Vector Container * * instead of an array. Here is an example below: * * * * Load the target file with a Multiplication Table * * * * * \*******************************************************/ // reading a text file #include <iostream> #include <fstream> #include <string> #include <vector> std::string user_file; int user_size = 2; void array_maker(int user_size, std::string user_file); int main () { std::cout << "Enter the name of the file for your data: "; std::cin >> user_file; std::cout << std::endl; std::cout << "Enter the size for your Multiplication Table: "; std::cin >> user_size; // Create the users Multiplication data array_maker(user_size, user_file); return (0); } void array_maker(int user_size, std::string user_file) { // Open file to write data & add it to end of file std::ofstream target_file(user_file,std::ios::out | std::ios::app); // Declare the vector to use as a runtime sized array std::vector<std::vector<int>> main_array; // Initialize the size of the vector array main_array.resize(user_size+1); // Outer Dimension for (int i=0; i <= user_size; ++i) // Inner Dimension { main_array[i].resize(user_size+1); } for (int i=0; i<=user_size; ++i) { for (int j=0; j<=user_size; ++j) { main_array[i][j] = i * j; // output line to current record in file target_file << i << "*" << j << "=" << main_array[i][j] << " " << "EOR" // End of Record << std::endl; } // Close Inner For } // Close Outer For // close file target_file.close(); } // Close array_maker function 

Answer 4

You can do void function (int ** __matrix, int32_t __row, int32_t __column) __row - maximum rows __column - maximum columns.

You will need these parameters to find out the limits of the array.

Answer 5

Just add another parameter to your function - row_number and column_number . Arrays are not objects in C ++, so they do not store any additional information about themselves.

Answer 6

If you pass in the array identifier (as a pointer to a pointer), you will need to use pointer arithmetic:

 void function(int** matrix, int num_rows, int num_cols) { Assert(matrix!=NULL && *matrix!=NULL && num_rows>0 && num_cols>0); for(int i=0; i<num_rows; i++) { for(int j=0; j<num_cols; j++) { // cannot index using [] like matrix[i][j] // use pointer arithmetic instead like: // *(matrix + i*num_cols + j) } } } 

Answer 7

pass multidimensional arays to a method that the compiler needs to know the depth of each field, so one solution is to use templates and the calling method in the usual way, and the compiler will guess the size of each field.

 template <size_t m> void method(int M[][m]) { for(int i=0; i<m; ++i) for(int j=0; j<m; ++j) { // do funny stuff with M[i][j] } } int main() { int M[5][5] = { {1,0,1,1,0}, {0,1,1,1,0}, {1,1,1,1,1}, {1,0,1,1,1}, {1,1,1,1,1} }; method(M); // also you can call with method<5>(M) // if you have different sizes for each dimension try passing them in args return 0; } 

Answer 8

 int r, c int *matrix = new int[r,c]; for (int i = 0; i < r; i++) { /*cout << "Enter data" << endl;*/ for (int j = 0; j < c; j++) { cin >> matrix[i,j]; } } 

Answer 9

void function (int & matrix [] [])