是否可以将变量作为结构成员传递？

Question

如果我有这样的结构：

    /* Defined structure with 3 integer as members */
typedef struct MyStruct MyStruct;
struct Myscruct{
    int x; 
    int y; 
    int z;
};

int main()
{
    Mystruct example;   // declared "example" with type "Mystuct"
    example.x=1;        // member 1 have value 1
    example.y=2;        // member 2 have value 2
    example.z=3;        // member 3 have value 3
    char c;
    printf("\nchoose witch member you want to print [ x, y or z]");
    scanf("%c", &c);
    while(getchar() != '\n');
    printf("%d", example.c); // this is the part i don't know is possible.
    return 0;
}

可以将不同的成员传递给最后一个 printf 而不是使用 if 的组合吗？如果是这样，它的语法是什么？

Answer 1

不，您不能使用运行时数据来引用源代码中的符号。不过，您可以付出更多的努力来实现特定代码的明显目标：

typedef struct MyStruct MyStruct;
struct Myscruct{
    int x; 
    int y; 
    int z;
};

int main()
{
    Mystruct example;   // declared "example" with type "Mystuct"
    example.x=1;        // member 1 have value 1
    example.y=2;        // member 2 have value 2
    example.z=3;        // member 3 have value 3
    char c;
    int xyz;

    printf("\nchoose witch membeer you want to print [ x, y or z]");
    scanf("%c", &c);
    switch (c) {
        case 'x':
            xyz = example.x;
            break;
        case 'y':
            xyz = example.y;
            break;
        case 'z':
            xyz = example.z;
            break;
        default:
            puts("Oops\n");
            return 1;
    }
    printf("%d", xyz);
    return 0;
}

还有其他选择，但是 none 与您尝试的一样直接。

Answer 2

你要的叫反射，C没有。

一个解决方案是让 Mystruct 包含一个数组：

struct Mystruct {
    int coordinates[3];
};

...
Mystruct example;
example.coordinates[0]=1;      
example.coordinates[1]=2;  
example.coordinates[2]=3;  
int i;

然后向用户询问一个数字，将其存储在i中并将其用作数组的索引：

printf("%d", example.coordinates[i]);

Answer 3

您可以使用 offsetof:

#include <stdio.h>
#include <stddef.h>

typedef struct MyStruct MyStruct;
struct MyStruct{
    int x; 
    int y; 
    int z;
};

int main()
{
    size_t addr[] = {
        offsetof(MyStruct, x),
        offsetof(MyStruct, y),
        offsetof(MyStruct, z),
    };
    MyStruct example;   // declared "example" with type "Mystuct"
    example.x=1;        // member 1 have value 1
    example.y=2;        // member 2 have value 2
    example.z=3;        // member 3 have value 3
    char c;
    printf("\nchoose witch membeer you want to print [ x, y or z]");
    scanf("%c", &c);
    printf("%d\n", *(int *)((char *)(&example) + addr[c - 'x']));
    return 0;
}

输出：

choose witch membeer you want to print [ x, y or z]y
2

是否可以将变量作为结构成员传递？

Is it possible to pass a variable as a structure member?

c

struct