指针做参数的动态内存分配与二重指针(下）

Posted 2020-10-12 Z.L.G

要实现指针作为函数形参，改变实参指针的值。一般有两种做法：

1. 使用双指针，或者指针数组形式作为形参，将实参的地址传入函数，也即要给形参传入指针的地址！

   http://blog.csdn.net/liuyajun2013/article/details/17151309#0-tsina-1-79483-397232819ff9a47a7b7e80a40613cfe

   http://www.cnblogs.com/heat-man/p/4646051.html

   http://www.jb51.net/article/37516.htm

2. 利用返回指针的函数直接返回分配好内存的地址（动态(堆)内存分配你懂的）

接上篇：为一个m行n列的二维数组开辟空间输入各元素的值，再然后输出。

方法一：直接分配一块连续的空间存放m * n个元素：

#include <stdio.h>
#include <stdlib.h>
#include <memory.h>
int main()
{
    void Input(int *pointer_1, int *pointer_2);      //输入行列
    int *allocation(int dimention);                  //分配内存
    void Output(int *pointer, int line, int column); //输出各元素值

    int m, n;
    int *pointer_counterpart;

    Input(&m, &n);
    pointer_counterpart = allocation(m * n);         //感觉还是要仔细，小错误很耽误事儿。例如pointer_counterpart = *allcation(m * n)
    Output(pointer_counterpart, m, n);

    free(pointer_counterpart);
    return 0;
}
void Input(int *pointer_1, int *pointer_2)
{
    printf ("Please input the line & column:\\n");
    scanf ("%d%d", pointer_1, pointer_2);
}
int *allocation(int dimention)
{
    int *pointer;
    printf ("Please input %d numbers:\\n", dimention);
    pointer = (int*)malloc(dimention * sizeof(int));   //分配了一块连续的空间,小细节要注意的点，强制类型转换(int *)
    memset(pointer, 0, dimention);
    for (int i = 0; i < dimention; ++i) {
        scanf ("%d", pointer + i);
    }
    return pointer;
}
void Output(int *pointer, int line, int column)
{
    int *pointer_copy;
    pointer_copy = pointer;
    printf ("The matrix is:\\n");
    for (int i = 0; i < line; ++i) {
        for (int j = 0; j < column; ++j) {
            printf ("%d ", *pointer_copy++);   //这种表达方式很好
        }
        printf ("\\n");
    }
    pointer_copy = pointer;

}

方法二：连续分配m块连续的空间各存放 n个元素：

#include <stdio.h>
#include <stdlib.h>


int **pointer_counterpart;           //要定义此全局变量
int main()
{
    void Input(int *pointer_1, int *pointer_2);
    void allocation(int line, int column);
    void display(int **pointer, int line, int column);
    void free_pointer(int **pointer, int line);

    int m, n;
    //int *pointer_counterpart[line];


    Input(&m, &n);
    allocation(m, n);
    display(pointer_counterpart, m, n);
    free_pointer(pointer_counterpart, m);
    //pointer_counterpart =

    return 0;
}
void Input(int *pointer_1, int *pointer_2)
{
    printf ("Please input the line & column:\\n");
    scanf ("%d%d", pointer_1, pointer_2);
}
void allocation(int line, int column)
{
    //int **pointer;  ///二重指针多与指针数组一同使用
    int *pointer_array[line];


    for (int i = 0; i < line; ++i) {
        pointer_array[i] = (int*)malloc(column * sizeof(int));
    }
    printf ("Please input %d *%d numbers:", line, column);
    for (int i = 0; i < line; ++i) {
        for (int j = 0; j < column; ++j) {
            scanf ("%d", pointer_array[i] + j);
        }
    }
    //pointer = pointer_array;
    pointer_counterpart = pointer_array;      ///全局变量指针指向了指针数组的首地址
}
void display(int **pointer, int line, int column)
{
    printf ("The matrix is:\\n");
    for (int i = 0; i < line; ++i) {
        for (int j = 0; j < column; ++j) {
            printf ("%d ", *(pointer[i] + j));
        }
        printf ("\\n");
    }
}
void free_pointer(int **pointer, int line)
{
    for (int i = 0; i < line; ++i) {
        free(pointer[i]);
    }
}