在结构中设置数组数据

Question

If when passing to functions we treat parameters uint32_t data[] and uint32_t* data as both being pointers to an array of data, why is the same not true when setting a member of a struct? Quick example:

#include <stdint.h> /* uint32_t */
#include <string.h> /* memcpy */
#include <stdlib.h> /* malloc */

typedef struct {
    uint32_t data[1024];
} tData;

typedef struct {
    uint32_t *data;
} pData;

int main()
{
    // structs
    pData pdata;
    tData sdata;
    
    // Test 1.
    ///////////////////////////////////
    uint32_t mydata[1024];
    
    // This is OK
    pdata.data = mydata;
    
    // This is not OK
    sdata.data = mydata;
    
    // But this is OK
    memcpy(sdata.data, mydata, 1024);
    
    // Test 2.
    ///////////////////////////////////
    uint32_t *otherdata = malloc(sizeof(uint32_t)*1024);
    
    // This is OK
    pdata.data = otherdata;
    
    // This is not OK
    sdata.data = otherdata;
    
    // But this is OK
    memcpy(sdata.data, otherdata, 1024);
}

In order to satisfy the struct tData must I do a memcpy ? Is this the only way?

Answer 1

It looks like an attempt to assign an array directly, something like this (without structs)

int A[10];
int B[10];
int  *ptr;
ptr = A;    // OK
A = B;      // Not ok

assigning array to pointer will make the pointer to point to the first element of the array, while comparing 2 arrays directly is not allowed.

The example with memcpy is equal to copying elements(their memory) one by one. so you can also do something like this.

for(int i = 0; i < 1024; ++i)
    sdata.data[i] = mydata[i];