C语言动态创建二维数组

在编程中有时需要使用二维数组作为buffer，下面是我写的一个二维数组的demo。

这里面涉及到几个内存操作的知识点，一个一个的来讲。

1. 创建两个1维数组，用于给二维数组填充值的时候使用。

/*2行27列，一维数组长度为27*/
#define BUFF_SIZE_ROW 2
#define BUFF_SIZE_COL 27

int main()
{
    
    /*初始化两个原子数据，全1和全2*/
    unsigned char data[BUFF_SIZE_COL];
    unsigned char data1[BUFF_SIZE_COL];

    /*memset整体为数组赋值某个值*/
    memset(data, 1, BUFF_SIZE_COL);
    memset(data1, 2, BUFF_SIZE_COL);
           

这一段包含两个知识点，一个是一位数字的创建，和一维数组的一个整体一次性赋值。用到的重点函数的memset。

2.动态创建二维数组，用法如下

unsigned char **buffer_a = (unsigned char **)malloc(BUFF_SIZE_ROW * sizeof(unsigned char *));
    for(int i = 0; i < BUFF_SIZE_ROW; i++)
    {
        buffer_a[i] = (unsigned char *)malloc(BUFF_SIZE_COL * sizeof(unsigned char));
    }
           

 3.将原子一维数组填充到动态创建的二维数组中

/*将原子数据赋值给buffer_a*/
    memcpy(buffer_a[0], data1, BUFF_SIZE_COL);
    memcpy(buffer_a[1], data1, BUFF_SIZE_COL);
           

这部分用到的知识点是memcpy，这里一定要注意copy的内存大小。

4.将一个动态创建的二维数组赋值给另外一个动态创建的二维数组

/*将buffer_a循环赋值给buffer_b*/
    for (size_t i = 0; i < BUFF_SIZE_ROW; i++)
    {
        memcpy(buffer_b[i], buffer_a[i], BUFF_SIZE_COL);
    }
           

这里注意buffer_b的创建方式与buffer_a一致。 

5.释放二维数组

/*释放buffer，先释放行，再释放列*/
    for(int i = 0; i < BUFF_SIZE_ROW; i++)
        free(buffer_a[i]);

    free(buffer_a);
    buffer_a = NULL; 
           

这里注意要先free掉列，再释放行，与创建时相反 

下面是完整的测试代码：

#include <stdio.h>
#include <windows.h>

/*2行27列，一维数组长度为27*/
#define BUFF_SIZE_ROW 2
#define BUFF_SIZE_COL 27

int main()
{
    
    /*初始化两个原子数据，全1和全2*/
    unsigned char data[BUFF_SIZE_COL];
    unsigned char data1[BUFF_SIZE_COL];

    /*memset整体为数组赋值某个值*/
    memset(data, 1, BUFF_SIZE_COL);
    memset(data1, 2, BUFF_SIZE_COL);

    /*创建二维动态数组buffer_a和buffer_b*/
    unsigned char **buffer_a = (unsigned char **)malloc(BUFF_SIZE_ROW * sizeof(unsigned char *));
    for(int i = 0; i < BUFF_SIZE_ROW; i++)
    {
        buffer_a[i] = (unsigned char *)malloc(BUFF_SIZE_COL * sizeof(unsigned char));
    }

    unsigned char **buffer_b = (unsigned char **)malloc(BUFF_SIZE_ROW * sizeof(unsigned char *));
    for(int i = 0; i < BUFF_SIZE_ROW; i++)
    {
        buffer_b[i] = (unsigned char *)malloc(BUFF_SIZE_COL * sizeof(unsigned char));
    }

    /*将原子数据赋值给buffer_a*/
    memcpy(buffer_a[0], data1, BUFF_SIZE_COL);
    memcpy(buffer_a[1], data1, BUFF_SIZE_COL);

    /*将buffer_a循环赋值给buffer_b*/
    for (size_t i = 0; i < BUFF_SIZE_ROW; i++)
    {
        memcpy(buffer_b[i], buffer_a[i], BUFF_SIZE_COL);
    }

    /*输出A B的第一行数据，验证是否等于data*/
    for (size_t i = 0; i < BUFF_SIZE_COL; i++)
    {
        printf("a %d, %d\r\n", i, buffer_a[0][i]);
    }
       
    for (size_t i = 0; i < BUFF_SIZE_COL; i++)
    {
        printf("b %d, %d\r\n", i, buffer_b[0][i]);
    }
    /*释放buffer，先释放列，再释放行*/
    for(int i = 0; i < BUFF_SIZE_ROW; i++)
        free(buffer_a[i]);

    free(buffer_a);
    buffer_a = NULL; 

    for(int i = 0; i < BUFF_SIZE_ROW; i++)
        free(buffer_b[i]);
    free(buffer_b);
    buffer_b = NULL; 

    system("pause");
	return 0;
}
 

           

linux kernel

int i, j;
    
    uint8_t **buffer_a = (uint8_t **)kmalloc(BUFF_SIZE * sizeof(uint8_t *), GFP_KERNEL);
    uint8_t **buffer_b = (uint8_t **)kmalloc(BUFF_SIZE * sizeof(uint8_t *), GFP_KERNEL);
    uint8_t data[SAMP_SIZE];

    memset(data, 0xff, SAMP_SIZE);

    for (i = 0; i < BUFF_SIZE; i++)
    {
        buffer_a[i] = (uint8_t *)kmalloc(SAMP_SIZE * sizeof(uint8_t), GFP_KERNEL);
    }
    
    for (i = 0; i < BUFF_SIZE; i++)
    {
        buffer_b[i] = (uint8_t *)kmalloc(SAMP_SIZE * sizeof(uint8_t), GFP_KERNEL);
    }
    calltime = ktime_get();
    for (i = 0; i < BUFF_SIZE; i++)
    {
        memcpy(buffer_a[i], data, SAMP_SIZE);
    }
    

    for (j = 0; j < 100; j++)
    {
        /* code */
        for (i = 0; i < BUFF_SIZE; i++)
        {
            memcpy(buffer_b[i], buffer_a[i], SAMP_SIZE);
        }
    }
    

    rettime = ktime_get();
    delta = ktime_sub(rettime, calltime);
    duration = (unsigned long long )ktime_to_ns(delta) >> 10;
    printk("buffer copy use %lld us\r\n", duration);

    /*free buffer*/
    for (i = 0; i < BUFF_SIZE; i++)
    {
        kfree(buffer_a[i]);
    }
    kfree(buffer_a);
    buffer_a = NULL; 
 
    for(i = 0; i < BUFF_SIZE; i++)
    {
        kfree(buffer_b[i]);
    }   
    kfree(buffer_b);
    buffer_b = NULL;