Dynamic assignment and parameter transfer of "reprint" two-dimensional array

This essay is reproduced, the original paste address: http://www.cnblogs.com/bigshow/archive/2009/01/03/1367661.html.

1. C-Language dynamic assignment of two-dimensional arrays(1) Second dimension known Code-1 char (*a) [n];//pointer to array a = (char (*) [N]) malloc (sizeof (char *) * m);p rintf ("%d\n", sizeof (a));//  4, pointer printf ("%d\n", sizeof (a[0]));//n, one-dimensional array free (a); (2) The first dimension is known Code-2 char* a[m];//pointer array int i; for (i=0; i<m; i++) a[i] = (char *) malloc (sizeof (char) * n);  printf ("%d\n", sizeof (a)),//4*m, pointer array printf ("%d\n", sizeof (A[0])),//4, pointer for (i=0; i<m; i++) Free (a[i]); (3) First dimension known, memory allocated at a time (guaranteed memory continuity) Code-3 char* a[m];//pointer array int i; a[0] = (char *) malloc (sizeof (char) * M * n); for (i=1; i<m; i++) A[i] = A[i-1] + N;   printf ("%d\n", sizeof (a)),//4*m, pointer array printf ("%d\n", sizeof (A[0])),//4, pointer Free (a[0]); (4) Two dimensions are unknown Code-4 char **a;int i; a = (char * *) malloc (sizeof (char *) * m);//allocation pointer array for (I=0; i<m; i++) { A[i] = (c Har *) malloc (sizeof (char) * n);//assigns each pointer to the array } printf ("%d\n", sizeof (a)),//4, pointer printf ("%d\n", sizeof (a[0]));// 4, pointer for (i=0; i<m; i++) {free (a[i]);}  Free (a); (5) Two-dimensional unknown, one-time allocation of memory (guaranteed memory continuity) Code-5 char **a;int i; a = (char * *) malloc (sizeof (char *) * m);//assignment pointer array a[0] = (char *) malloc (sizeof (char) * m * n);//One-time allocation of all spaces for (i=1; i<m; i++) { a[i] = a[i-1] + N;} printf ("%d\n", sizeof (a)),//4, pointer printf ("%d\n", size  Of (a[0]));//4, pointer Free (a[0]); 2.c++ Dynamic allocation of two-dimensional arrays(1) Second dimension known Code-6 char (*a) [n];//pointer to array a = new char[m][n]; printf ("%d\n", sizeof (a)),//4, pointer printf ("%d\n", sizeof (a[  0]));//n, one-dimensional array delete[] A; (2) The first dimension is known Code-7 char* a[m];//pointer array for (int i=0; i<m; i++) a[i] = new Char[n]; printf ("%d\n", sizeof (a)),//4*m, number of pointers  Group printf ("%d\n", sizeof (A[0])),//4, pointer for (i=0; i<m; i++) delete[] a[i]; (3) First dimension known, memory allocated at a time (guaranteed memory continuity) Code-8 char* a[m];//pointer array a[0] = new char[m*n];for (int i=1; i<m; i++) a[i] = a[i-1] + N; printf (   "%d\n", sizeof (a));//4*m, pointer array printf ("%d\n", sizeof (a[0]));//4, Pointer delete[] a[0]; (4) Two dimensions are unknown Code-9 char **a;a = new char* [m];//allocation pointer array for (int i=0; i<m; i++) { A[i] = new char[n];//assigns the array to which each pointer points /c5>} printf ("%d\n", sizeof (a)),//4, pointer printf ("%d\n", sizeof (A[0])),//4, pointer for (i=0; i<m; i++) delete[] a[i];  Delete[] A; (5) Two-dimensional unknown, one-time allocation of memory (guaranteed memory continuity) Code-10 char **a;a = new char* [m];a[0] = new CHAR[M * n];//One-time allocation of all spaces for (int i=1; i<m; i++) { A[i] = A[I-1] + n;//assigns each pointer to the array } printf ("%d\n", sizeof (a)),//4, pointer printf ("%d\n", sizeof (A[0])),//4, Pointer delete[] a[0];  Delete[] A; One more word: New and delete to pay attention to pairing, that is, how many new will have the number of delete, so as to avoid memory leaks! 3. Static two-dimensional arrays are passed as function parametersIf the two-dimensional arrays are dynamically allocated using the above methods, then the corresponding data types can be used as function parameters. Here, the static two-dimensional array is passed as a function parameter, that is, by calling the following method: Int A[2][3];func (a); In C language, it is troublesome to pass a static two-dimensional array as a parameter, it is usually necessary to indicate the length of the second dimension, if the second dimension is not given, it can only be passed as a one-dimensional pointer, then the linear storage property of the two-dimensional array is transformed into the access to the specified element in the function body. First write the test code to verify the correctness of the parameter passing: (1) Given the second dimension length Code-11 void func (int a[][n]) { printf ("%d\n", a[1][2]);} (2) Not given a second dimensional length Code-12 void func (int* a) { printf ("%d\n", a[1 * n + 2]);//compute element position } Note: When using this function, you need to cast the first address of the two-dimensional array to a one-dimensional pointer, func ((int*) a).

Dynamic assignment and parameter transfer of "reprint" two-dimensional array