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。但是，您可以通过更多的努力来完成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，但没有一个像你尝试的那样直接。

Answer 2

你想要的是反射，而C却没有。

一种解决方案是让Mystruct包含数组：

struct Mystruct {
    int coordinates[3];
};

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

然后询问用户一个数字，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？

3 个答案: