However, both dimensions of a two-dimensional array at run time the array must be dynamically allocated grant. A two-dimensional array dynamically allocated should be considered in this case as an array of one-dimensional arrays. Some effort of memory, but the assignment must be an array of arrays, pointers, which are not necessary defined static two-dimensional arrays. Despite the effort, each element of the two-dimensional arrays with the bracket notation just like a statically defined two-dimensional array can be referenced.
These are the steps for a two-dimensional array dynamically reserve:
Declare a double dereferenced pointer of the desired type. Reserve the number of lines the size of a pointer dereference and assign to the first at the beginning of this assignment. Go through the lines and reserve the number of column size of the element.
Code:
Array of Arrays of Pointers element ------ ------------------------- ------- | | -> | | | | | | |. . . . . . . | | ------ ------------------------- ------- | | -> | | | | | | |. . . . . . . | | ------ ------------------------- ------- | | -> | | | | | | |. . . . . . . | | ------ ------------------------- ------- | | -> | | | | | | |. . . . . . . | | ------------------------- ------ -------..... ------------------------- ------- | | -> | | | | | | |. . . . . . . | | ------ ------------------------- ------- | | -> | | | | | | |. . . . . . . | | ------ ------------------------- -------
_fmalloc (use) for MS-DOS and 16-bit Windows, to use the wide or global heap. Note for Windows: _fmalloc () is available when compiling with Microsoft C / C + + compiler versions 7.0, 8.0 and 8.0 c are used. Do not use GlobalAlloc and GlobalLock, since this technology can use up to many selectors for relatively small allocations.
Unlike a static two-dimensional array declared the lines are not interrelated. As this is an array of arrays it is possible, however, an entire structure is greater than 64 KB without a big hand. If the number of rows or the size of the lines is greater than 64 KB, extensive hands are needed.
A small example :
/ * Semi-pseudo code for a two-dimensional array of char's *
Note that this sample uses the far heap and uses far pointers. *
For 32-bit Windows applications on Windows NT or Win32S or for * OS / 2,
use malloc ( ) and remove the _far keywords;. * / char *
_far _far unsigned
int * array,
unsigned int rows, columns,
/ * let's keep it within 64k * /
/ * Set the rows and columns to desired dimensions. * /
Rows = 8;
columns = 12;
array = (char * _far _far *)
_fmalloc (sizeof (char _far *) * rows)
if (array == NULL) (printf ("Not enough memory \ n");
return
for (i = 0; i <rows; i + +)
(array [i] = (char _far *) _fmalloc (sizeof (char) * columns)
if (array [i] == NULL) (printf (" not memory \ n enough "),
/ * handle error, _free (the previously allocated rows * /
return))
/ * to use the array: array [row] [column] * /
array [0] [1] = 'x'
/ * etc. * / To * Free the memory used by the array ** * /
for (i = 0; i <rows; i + +) _ffree (array [i]); _ffree (array);
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