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]);
c语言char的用法
}
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;

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