Memory Allocation and release of multi-dimensional arrays in C Language (malloc and free)

When writing code, you may encounter the issue of memory allocation and release of multi-dimensional arrays. errors may occur during the allocation and release processes. The following is a sample code for your reference.

 

To allocate space to a two-dimensional array (M * n), the code can be written as follows:

Char ** A, I; // Allocate M pointer units first. Note that they are pointer units. // The size of each unit is sizeof (char *) A = (char **) malloc (M * sizeof (char *)); // Assign n character units, // The above M pointer units point to the first address of the N character units For (I = 0; I <m; I ++) A [I] = (char *) malloc (N * sizeof (char ));

(Pay attention to the red part)

Release should be:

Int I; For (I = 0; I <m; I ++) Free (void *) A [I]); Free (void *) );

If space is allocated for a three-dimensional array (M * n * P), it should be:

Char *** A, I, J; A = (char ***) malloc (M * sizeof (char **)); For (I = 0; I <m; ++ I) A [I] = (char **) malloc (N * sizeof (char *)); For (I = 0; I <m; ++ I) For (j = 0; j <n; ++ J) A [I] [J] = (char *) malloc (p * sizeof (char ));

The release code is an inverse process. The specific code is:

Int I, j ,; For (I = 0; I <m; ++ I) For (j = 0; j <n; ++ J) Free (void *) A [I] [J]); For (I = 0; I <m; ++ I) Free (void *) A [I]); Free (void *) );

 

The principles of allocation and release of multidimensional arrays above three dimensions are the same as those above.

(Transfer)

 

What is the second-Dimensional Fixed two-dimensional array allocation memory in C?

In the code, sometimes the memory needs to be allocated to a two-dimensional array. The first-dimensional length of the two-dimensional array is not fixed, the second dimension is fixed (like the array of ARR [N] [3 ). We can think of a double pointer instead of an array. Of course, we can also directly assign a value to n to define arr [N] [3] (supported by the c99 standard ), but here is another method.

Here, we take reading the point cloud data into a two-dimensional array as an example. because the number of points in the point cloud is N, we can determine that the point is a three-dimensional point. You can define and allocate the memory in the following way:

Double (* ARR) [3] = malloc (N * 3 * sizeof (double ));

But in the VC compiling environment, an error will be reported --Cannot be converted from "Void *" to "Double (*) [3]"In this case, type conversion should be performed before the malloc function. How should we convert it? How can we convert it to the double (*) [3] type? The conversion can be as follows:

Double (* ARR) [3] = (double (*) [3]) malloc (N * 3 * sizeof (double ));

Done! :).