C memcpy unsigned char 到 1 元素 unsigned char 数组用于校验和计算

Question

有一个字符数组ACKbuffer[2]，所以我首先将我想要的元素转换为unsigned char，但当我尝试时，它给了我一个错误>memcpy 将其转换为 unsigned char 数组。

//first element is checksum
unsigned char ack_csum;
ack_csum = (unsigned char)ACKbuffer[0];
//second element is ACK which needs to be run through checksum 
//in a checksum function that accepts unsigned char array as parameter
unsigned char ACK_actual = (unsigned char)ACKbuffer[1];
unsigned char ACK [1];
memcpy(ACK, ACK_actual, 1);

错误:

note: expected ‘const void * restrict’ but argument is of type ‘unsigned char’
 extern void *memcpy (void *__restrict __dest, const void *__restrict __src,
              ^~~~~~
swap_client.c: In function ‘swap_write’:
swap_client.c:185:17: warning: passing argument 2 of ‘memcpy’ makes pointer from integer without a cast [-Wint-conversion]
     memcpy(ACK, ACK_actual, 1);

我也尝试了另一种方法，但我得到无效的初始化程序:

unsigned char ACK_actual = (unsigned char)ACKbuffer[1];
unsigned char ACK [1] = ACK_actual;

理想情况下，我希望我的 ACK 数组保存来自 ACKbuffer 的该值。

Answer 1

在memcpy的调用中

memcpy(ACK, ACK_actual, 1);

变量 ACK_actual 的类型为 unsigned char

unsigned char ACK_actual = (unsigned char)ACKbuffer[1];

但该函数需要指针类型。

直接写

memcpy(ACK, ACKbuffer + 1, 1);

至于第二个代码片段，你应该这样写

unsigned char ACK_actual = (unsigned char)ACKbuffer[1];
unsigned char ACK [1] = { ACK_actual };