malloc, free, new, delete

The processing of an indefinite-size multidimensional array in C language:

If you want to allocate space for a two-dimensional array (m*n), the code can be written as follows:

Char **a, I; Allocate m pointer units First, note that the pointer unit So the size of each unit is sizeof (char *) A = (char * *) malloc (M * sizeof (char *)); and allocate n character cells, The M-pointer unit above points to this N-character single head address for (i = 0; i < m; i++) A[i] = (char *) malloc (n * sizeof (char));

The release should be:

int i; for (i=0;i<m;i++) Free (void *) a[i]); Free (void *) a);

If you allocate space 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));

Release the code as a reverse process, with the following code:

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 *) a);

The allocation and release of multidimensional arrays of more than three dimensions is the same as above.

How to allocate memory for two-dimensional arrays with fixed second-dimension lengths in C

In the code that is written, it is sometimes necessary to allocate memory for a two-dimensional array, the first dimension of the two-dimensional array is indefinite, and the second dimension is a fixed (like arr[n][3] array). What we can think of is the use of double pointers instead of arrays, of course, you can directly define ARR[N][3] (C99 standard support), but here's another way to say it.

To read the point cloud data into a two-dimensional array, for example, because the point cloud points n variable, it can be determined that the point is a three-dimensional point, you can define and allocate memory in the following ways:

Double (*arr) [3] = malloc (n*3*sizeof (double));

However, in the VC compilation environment, will be error-can not be converted from "void *" to "double (*) [3]" , this time should be in the malloc function before the type conversion, how should be converted? How to convert to a double (*) [3] type, you can convert as follows:

Double (*arr) [3] = (double ((*) [3]) malloc (n*3*sizeof (double));

Get! ：）。

Third, C + + 's new delete

1. Common types (structure, class, etc.):

Int* A;

a=new int;

*a=3;

Delete A;

2. Arrays:

Int* A;

A=new Int[num];

delete []a;

malloc, free, new, delete