c语言回顾—数组与指针

**http://home.netcom.com/~tjensen/ptr/ch9x.htm**
#include 
//Array and pointer written by Mr Ding
int main(){
    int a[2][2];
    a[0][0]=0;
    a[0][1]=1;
    a[1][0]=2;
    a[1][1]=3;
    printf("%p\n",a);
    printf("%p\n",a[0]);
    printf("%p\n",a[1]);
    printf("%p\n",&a[1][0]);
    printf("%p\n",a+1);
    printf("%p\n",*(a+1));
    printf("%d\n",**(a+1)); 
    printf("%p\n",*(a+2));
    printf("%d\n",**(a+2));
    printf("%d\n",a[2][0]);
    printf("%d\n",(*a)[0]);
    printf("%d\n",(*(a+1))[0]);
    return 0;
}

运行结果：

思考点：数组编译成指针表示，越界读取的原因

注意：1.char multi[5][10];
Let’s take the underlined part to be the “name” of an array. Then prepending the char and appending the [10] we have an array of 10 characters. But, the name multi[5] is itself an array indicating that there are 5 elements each being an array of 10 characters. Hence we have an array of 5 arrays of 10 characters each..

2.In fact, in general all dimensions of higher order than one are needed when dealing with multi-dimensional arrays. That is if we are talking about 3 dimensional arrays, the 2nd and 3rd dimension must be specified in the parameter definition.

经典代码
指针和内存的动态分配

    int** array_pointer;

    array_pointer = (int **)malloc(r * sizeof(int*));

    for (i=0; iint *)malloc(c * sizeof(int));
    }

      ……

    for(i = 0; i < r; i++)  {
      free(array_pointer[i]);
      array_pointer[i] = NULL;
    }

    if (array_pointer != NULL) {
      free(array_pointer);
    }

    return 0;
} //come from my code

方法2
核心代码

#include 
#include 

int main(void)
{
    int **rptr;
    int *aptr;
    int *testptr;
    int k;
    int nrows = 5;     /* Both nrows and ncols could be evaluated */
    int ncols = 8;    /* or read in at run time */
    int row, col;

    /* we now allocate the memory for the array */

    aptr = malloc(nrows * ncols * sizeof(int));
    if (aptr == NULL)
    {
        puts("\nFailure to allocate room for the array");
        exit(0);
    }

    /* next we allocate room for the pointers to the rows */

    rptr = malloc(nrows * sizeof(int *));
    if (rptr == NULL)
    {
        puts("\nFailure to allocate room for pointers");
        exit(0);
    }

    /* and now we 'point' the pointers */

    for (k = 0; k < nrows; k++)
    {
        rptr[k] = aptr + (k * ncols);//核心代码！！！
    }

    /* Now we illustrate how the row pointers are incremented */
    printf("\n\nIllustrating how row pointers are incremented");
    printf("\n\nIndex   Pointer(hex)  Diff.(dec)");

    for (row = 0; row < nrows; row++)
    {
        printf("\n%d         %p", row, rptr[row]);
        if (row > 0)
        printf("              %d",(rptr[row] - rptr[row-1]));
    }
    printf("\n\nAnd now we print out the array\n");
    for (row = 0; row < nrows; row++)
    {
        for (col = 0; col < ncols; col++)
        {
            rptr[row][col] = row + col;
            printf("%d ", rptr[row][col]);
        }
        putchar('\n');
    }

    puts("\n");

    /* and here we illustrate that we are, in fact, dealing with
       a 2 dimensional array in a contiguous block of memory. */
    printf("And now we demonstrate that they are contiguous in memory\n");

    testptr = aptr;
    for (row = 0; row < nrows; row++)
    {
        for (col = 0; col < ncols; col++)
        {
            printf("%d ", *(testptr++));
        }
        putchar('\n');
    }

    return 0;
}

三维数组的动态分配

#include 
#include 
#include 

int X_DIM=16;
int Y_DIM=5;
int Z_DIM=3;

int main(void)
{
    char *space;
    char ***Arr3D;
    int y, z;
    ptrdiff_t diff;

    /* first we set aside space for the array itself */

    space = malloc(X_DIM * Y_DIM * Z_DIM * sizeof(char));

    /* next we allocate space of an array of pointers, each
       to eventually point to the first element of a
       2 dimensional array of pointers to pointers */

    Arr3D = malloc(Z_DIM * sizeof(char **));

    /* and for each of these we assign a pointer to a newly
       allocated array of pointers to a row */

    for (z = 0; z < Z_DIM; z++)
    {
        Arr3D[z] = malloc(Y_DIM * sizeof(char *));

        /* and for each space in this array we put a pointer to
           the first element of each row in the array space
           originally allocated */

        for (y = 0; y < Y_DIM; y++)
        {
            Arr3D[z][y] = space + (z*(X_DIM * Y_DIM) + y*X_DIM);
        }
    }

    /* And, now we check each address in our 3D array to see if
       the indexing of the Arr3d pointer leads through in a
       continuous manner */

    for (z = 0; z < Z_DIM; z++)
    {
        printf("Location of array %d is %p\n", z, *Arr3D[z]);
        for ( y = 0; y < Y_DIM; y++)
        {
            printf("  Array %d and Row %d starts at %p", z, y, Arr3D[z][y]);
            diff = Arr3D[z][y] - space;
            printf("    diff = %d  ",diff);
            printf(" z = %d  y = %d\n", z, y);
        }
    }
    return 0;

指向函数的指针

#include 
#include 

#define MAX_BUF 256

long arr[10] = { 3,6,1,2,3,8,4,1,7,2};
char arr2[5][20] = {  "Mickey Mouse",
                      "Donald Duck",
                      "Minnie Mouse",
                      "Goofy",
                      "Ted Jensen" };

void bubble(void *p, int width, int N,
            int(*fptr)(const void *, const void *));
int compare_string(const void *m, const void *n);
int compare_long(const void *m, const void *n);

int main(void)
{
    int i;
    puts("\nBefore Sorting:\n");

    for (i = 0; i < 10; i++)               /* show the long ints */
    {
        printf("%ld ",arr[i]);
    }
    puts("\n");

    for (i = 0; i < 5; i++)                  /* show the strings */
    {
        printf("%s\n", arr2[i]);
    }
    bubble(arr, 4, 10, compare_long);          /* sort the longs */
    bubble(arr2, 20, 5, compare_string);     /* sort the strings */
    puts("\n\nAfter Sorting:\n");

    for (i = 0; i < 10; i++)             /* show the sorted longs */
    {
        printf("%d ",arr[i]);
    }
    puts("\n");

    for (i = 0; i < 5; i++)            /* show the sorted strings */
    {
        printf("%s\n", arr2[i]);
    }
    return 0;
}

void bubble(void *p, int width, int N,
            int(*fptr)(const void *, const void *))//目的是让bubble具有不同类型的通用性
{
    int i, j, k;
    unsigned char buf[MAX_BUF];
    unsigned char *bp = p;

    for (i = N-1; i >= 0; i--)
    {
        for (j = 1; j <= i; j++)
        {
            k = fptr((void *)(bp + width*(j-1)), (void *)(bp + j*width));
            if (k > 0)
            {
                memcpy(buf, bp + width*(j-1), width);
                memcpy(bp + width*(j-1), bp + j*width , width);
                memcpy(bp + j*width, buf, width);
            }
        }
    }
}

int compare_string(const void *m, const void *n)
{
    char *m1 = (char *)m;
    char *n1 = (char *)n;
    return (strcmp(m1,n1));
}

int compare_long(const void *m, const void *n)
{
    long *m1, *n1;
    m1 = (long *)m;
    n1 = (long *)n;
    return (*m1 > *n1);
}