将结构分配给多个结构成员

Question

I would like to initialize several members of a structure by assigning a "matching" structure to the members without explicitly assigning each member.

Here is an example to better explain it. I have two structures:

typedef struct
{
    void* ThingB;
    void* ThingC;
}SomeThings_S;

typedef struct
{
    void* ThingA;
    void* ThingB;
    void* ThingC;
}AllThings_S;

I would like initialize members ThingB and ThingC in AllThings_S by directly assigning Somethings_S to members ThingB and ThingC in AllThings_S. See the following:

void* ThingA;
void* ThingB;
void* ThingC;

SomeThings_S SomeThings =
{
    ThingB,
    ThingC,
};

AllThings_S AllThings =
{
    .ThingA = ThingA,
    SomeThings, <--- This is where I'm not sure how to proceed.
}

I can do the following:

AllThings_S AllThings =
{
    .ThingA = ThingA,
    .ThingB = SomeThings.ThingB,
    .ThingC = SomeThings.ThingC,
}

But this is what I'd like to avoid. I'd prefer if I can directly assign Somethings to ThingB and ThingC in AllThings.

Sorry. I had a hard time to trying and explain. Hope it is readable.

Answer 1

If you really want to do this--and I want to stress that I really don't advise this--you can make use of the -fplan9-extensions or -fms-extensions option in gcc that allows you to access members of anonymous structs directly. If using clang, use -fms-extensions as it does not have the plan9 extensions last I knew.

What it may look like:

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

typedef struct
{
    void* ThingB;
    void* ThingC;
}SomeThings_S;

typedef struct
{
    void* ThingA;
    SomeThings_S;
}AllThings_S;

int main(void) {

    int a;
    int b;
    int c;
    SomeThings_S x = {&a,&b};
    AllThings_S y = {&c, x};

    printf("%p, %p, %p\n", y.ThingA, y.ThingB, y.ThingC);

    return EXIT_SUCCESS;
}

Answer 2

I solved this with the comment from EOF by using an anonymous union and structure.