[英]How to pass a member of a struct to a function by reference in C?
I am trying to pass a member of a stuct to a function in c by reference and then use it to access the same member of a struct of the same type. 我试图通过引用将结构的成员传递给c中的函数,然后使用它来访问相同类型的结构的相同成员。
typedef struct Node
{
int a;
int b;
int c;
} Node;
Node mynode; //global
void pass_member(int *member){
mynode.&member = 1;//gives a compiler error
}
void main()
{
mynode.a = 0;
mynode.b = 45;
mynode.c = 64;
pass_member(&mynode.a)
}
I can see that mynode.&member
is not allowed in c but i think it shows what i am trying to do 我可以看到mynode.&member
在c中是不允许的,但是我认为它表明了我正在尝试做的事情
is it possible to pass the address of an member of a struct to a function in c 是否可以将结构的成员地址传递给c中的函数
and then use it to access that member in a struct of the same type? 然后使用它来访问相同类型的结构中的成员?
basically what i am trying to achieve is a function somthing like this 基本上我想要实现的是这样的功能
void set_member(int value_to_set, int * pointer_to_member_of_which_to_set);
that would set a specific member of a global struct depending on the given member to the function. 这将根据函数的给定成员设置全局结构的特定成员。
I will give you some example first:- 我先给你一个例子:
You can do it like this func(&mynode)
. 您可以这样执行func(&mynode)
。
And func
is void func(Node* aa)
而func
是void func(Node* aa)
Now you can use it like this 现在您可以像这样使用它
aa->a = aa->a + 1
etc. aa->a = aa->a + 1
等
Most of the time you will send the address of the whole structure rather than the address of the individiual element. 大多数情况下,您将发送整个结构的地址,而不是单个元素的地址。
Node aa
=> aa is of type struct node (typedefed to Node) Node aa
=> aa是struct node类型(类型定义为Node)
It's address: &aa
地址: &aa
aa.a
is the element of the structure aa
and it's address is &aa.a
aa.a
是结构aa
的元素,其地址为&aa.a
void pass_member(int *member){ *member = 1; }
pass_member(&mynode.a) // in main()
Also you can use it like this:- 您也可以像这样使用它:
typedef struct Node
{
int a;
int b;
int c;
} Node;
Node mynode; //global
void pass_member(Node *member){
(*member).a = 1;//member->a = 1
}
void main()
{
mynode.a = 0;
mynode.b = 45;
mynode.c = 64;
pass_member(&mynode)
}
You asked is it possible to pass the address of an member of a struct to a function in c? 您问是否可以将结构成员的地址传递给c中的函数?
Ans: Yes it is possible, it is shown in the answer. 回答:是的,有可能,答案中会显示。
and then use it to access that member in a struct of the same type? 然后使用它来访问相同类型的结构中的成员?
You can access that memebr be it of some struct or some other struct. 您可以访问该memebr,无论是某些结构还是其他结构。 As long as it is a pointer to an appropriate type it's possible. 只要它是指向适当类型的指针,就可以。
You have two options, either pass pointer to the member variable as 您有两个选择,可以将指针传递给成员变量:
void pass_member(int *member){
*member = 1;
and 和
pass_member(&mynode.a);
OR pass pointer to the entire structure 或传递指向整个结构的指针
void pass_member(Node *member){
(*member).a = 1; //or member->a = 1; as pointed out in comments
and 和
pass_member(&mynode)
You can use offsetof
to get the relative address of a member. 您可以使用offsetof
获得成员的相对地址。 I am unaware of a reverse operation (don't do much in C), but it can be simulated like this: 我不知道反向操作(在C语言中不做很多事情),但是可以这样模拟:
#define offsetin(s,a,t) *((t*)(((char*)&s)+a))
Then your code would look like this: 然后您的代码将如下所示:
void pass_member(size_t member){
offsetin(mynode, member, int) = 1;
}
void main()
{
mynode.a = 0;
mynode.b = 45;
mynode.c = 64;
pass_member(offsetof(Node,a));
}
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