c++ - How can I modify elements inside vectors? -

i'm trying modify elements inside vector. after change block in array , display again, won't show new values instead, retain previous output. doing wrong?

//////////////////////////////////////////////////// // displays array/maze //////////////////////////////////////////////////// void displaymaze( vector< vector<char> > &maze ) {     for( int = 0; < row; i++ ) {         for( int j = 0; j < col; j++ ) {             cout << "[" << maze[ ][ j ] << "] ";         }         cout << endl;     } }  //////////////////////////////////////////////////// // change element //////////////////////////////////////////////////// void updatemouse( vector< vector<char> > maze, const int &mouse_row, const int &mouse_col ) {     for( int row = 0; row < row; row++ ){         for( int col = 0; col < col; col++ ) {             if( ( row == mouse_row ) && ( col == mouse_col ) ) {                 maze[ row ][ col ] = 'm';                 break;             }         }     } } 

updatemouse takes maze argument by value. changes makes vector made local copy within function, destroyed when function exits. change function takes maze argument by reference.

void updatemouse( vector<vector<char>>& maze, const int &mouse_row, const int &mouse_col ) { //                                   ^^^ 

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the updatemouse function can simplified to

void updatemouse( vector<vector<char>>& maze, int mouse_row, int mouse_col ) {     if(mouse_row < maze.size()) {         if(mouse_col < maze[mouse_row].size()) {             maze[mouse_row][mouse_col] = 'm';         }     } }