将Struct复制到函数C中的指针数组

i have a huge problem allocating memory in C

在C中分配内存有一个很大的问题

i have this struct

我有这个结构体

typedef struct{
int x;
int y;
}T;

i want to create a function that dynamically adds a structs to a pointer. something like:

我想创建一个函数来动态地向指针添加结构。喜欢的东西:

int main()
{
 T* t;
 f(&t);
 free(t);
}

up to this point i think everything is ok, now the function is where i get lost

到目前为止，我认为一切都没问题，现在的功能就是我迷失的地方。

void f(T** t)
{
 T t1;
 T t2;
 T t3;
 //first i malloc
 *t=malloc(sizeof(T)*T_MAX_SIZE);//i want another function to make the array bigger, but this is not as important as the problem
 t1.x=11;
 t1.y=12;
 t2.x=21;
 t2.y=22;
 t3.x=31;
 t3.y=32;
//now i want to copy the values from t1,t2,t3 to t[0],t[1],t[2]
 memcpy(&(*t[0]),&t1,sizeof(T));
 memcpy(&(*t[1]),&t2,sizeof(T));
 memcpy(&(*t[2]),&t3,sizeof(T));


}

i do not know the correct way of copying these structs.

我不知道复制这些结构体的正确方法。

the point of doing this is to use t out of the function (in the main)

这样做的目的是在函数中使用t(主)

many thanks :D

非常感谢:D

2 个解决方案

#1

Your memcpy calls are incorrect.

你的memcpy调用不正确。

In the expression &(*t[0]), the array index has top precedence, followed by the pointer indirection. So with explicit parenthesis it looks like &(*(t[0])).

在表达式&(*t[0])中，数组索引优先级最高，然后是指针间接。因此有了显式括号，它看起来像&(*[0])。

So it first tries to array subscript t, which is the address of t in main. In the case of t[0] it still works, but t[1] references something past that variable, invoking undefined behavior. You want the array index of what t points to, which is (*t)[i].

它首先尝试数组下标t，也就是主地址t。对于t[0]，它仍然可以工作，但是t[1]引用那个变量之后的东西，调用未定义的行为。你想要的是t指向的数组下标，也就是(*t)[i]。

So the memcpy calls should be:

所以memcpy调用应该是:

memcpy(&((*t)[0]),&t1,sizeof(T));
memcpy(&((*t)[1]),&t2,sizeof(T));
memcpy(&((*t)[2]),&t3,sizeof(T));

#2

You don't need any copy functions to assign one structure to another - you simply equate them. So if you have

您不需要任何复制函数来将一个结构分配给另一个结构——您只需将它们等同起来。所以如果你有

T var1 = {1, 2};
T var2 = var1;

the whole of var1 is copied to var2. Amending your (simplified) program:

整个var1被复制到var2。修改你的(简化)计划:

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

#define T_MAX_SIZE 10

typedef struct{
    int x;
    int y;
}T;

void f(T** t)
{
    T t1;
    *t=malloc(sizeof(T)*T_MAX_SIZE);
    t1.x=11;
    t1.y=12;
    (*t)[0] = t1;
}

int main(void) {
    T* t;
    f(&t);
    printf ("Result %d %d\n", t[0].x, t[0].y);
    free(t);
    return 0;
}

Program output:

项目输出:

Result 11 12

#1