c - 在C中将数据从一个结构复制到另一个结构

Question

如果我的结构定义如下：

struct image{
unsigned int width, height;
unsigned char *data;
};

和这种类型的 2 个变量：

struct image image1;
struct image image2;

我想将数据从 image1 传输到 image2 的数据（假设 image1 写入了一些数据，而 image2 有分配了 malloc 或 calloc 的数据）。怎么做到呢？非常感谢。

Answer 1

Assuming it is undesirable that two instances of struct image are pointing to the same data then memcpy() cannot be used to copy the structs. To copy:

• allocate memory for destination struct
• allocate memory for destination data buffer based on source data
• assign width members
• memcpy() data members.

For example:

struct image* deep_copy_image(const struct image* img)
{
    struct image* result = malloc(sizeof(*result));
    if (result)
    {
        /* Assuming 'width' means "number of elements" in 'data'. */
        result->width = img->width;
        result->data = malloc(img->width);
        if (result->data)
        {
            memcpy(result->data, img->data, result->width);
        }
        else
        {
            free(result);
            result = NULL;
        }
    }
    return result;
}

Answer 2

你试过 memcpy(&image1,&image2,sizeof(image));

编辑：为 image2.data 分配数据，如果数据为空终止，则必须 strcpy(image2.data,image1.data) ，但如果不是，则使用 memcpy 和数据大小。

问候，卢卡

Answer 3

struct image image1;
struct image image2;

...

image2.width = image1.width;
image2.height = image1.height;

/* assuming data size is width*height bytes, and image2.data has enough space allocated: */

memcpy(image2.data, image1.data, width*height);

Answer 4

It's simple in C.Simply do the following(assuming image2 is uninitialized):

image2=image1;  //there's no deep copy, pointed to memory isn't copied

You can assign one structure variable to other given they are of the same type.No need to copy piece-meal.This is a useful feature of C.

This has been discussed before :

Assign one struct to another in C

Answer 5

如果您想要的只是复制结构（即创建“浅”副本）：

image2 = image1;

如果您还想复制（“深拷贝”）指向的数据image1.data，那么您需要手动执行此操作：

memcpy(image2.data, image1.data, image1.width * image1.height);

（假设数据中有image1.width * image1.height字节，并且有足够的空间malloc()来image2.data存储它。）