我构建了一种动态数组(向量),但并没有将数据(通常是void *
)嵌入到struct vector
中,而是为一个struct vector
+一个字节块保留了空间,这是一个使用size_t
数组的示例:
#include <stdio.h>
#include <stdlib.h>
struct vector {
size_t capacity;
size_t typesize;
size_t size;
};
#define VECTOR(v) ((struct vector *)((unsigned char *)v - sizeof(struct vector)))
static void *valloc(size_t typesize, size_t size)
{
struct vector *vector;
unsigned char *data;
data = calloc(1, sizeof(*vector) + typesize * size);
if (data == NULL) {
return NULL;
}
vector = (struct vector *)data;
vector->typesize = typesize;
vector->capacity = size;
vector->size = 0;
return data + sizeof(*vector);
}
static void *vadd(void *data)
{
struct vector *vector = VECTOR(data);
unsigned char *new;
size_t capacity;
if (vector->size >= vector->capacity) {
capacity = vector->capacity * 2;
new = realloc(vector, sizeof(*vector) + vector->typesize * capacity);
if (new == NULL) {
return NULL;
}
vector = (struct vector *)new;
vector->capacity = capacity;
vector->size++;
return new + sizeof(*vector);
}
vector->size++;
return data;
}
static size_t vsize(void *data)
{
return VECTOR(data)->size;
}
static void vfree(void *data, void (*func)(void *))
{
struct vector *vector = VECTOR(data);
if (func != NULL) {
for (size_t iter = 0; iter < vector->size; iter++) {
func(*(void **)((unsigned char *)data + iter * vector->typesize));
}
}
free(vector);
}
int main(void)
{
size_t *data;
data = valloc(sizeof(size_t), 1);
if (data == NULL) {
perror("valloc");
exit(EXIT_FAILURE);
}
for (size_t i = 0; i < 10; i++) {
data = vadd(data);
if (data == NULL) {
perror("vadd");
exit(EXIT_FAILURE);
}
data[i] = i;
}
for (size_t i = 0; i < vsize(data); i++) {
printf("%zu\n", data[i]);
}
vfree(data, NULL);
return 0;
}
问题是:malloc
(void *
)结果的地址+ struct
的大小对于任何类型都是对齐的吗?这段代码的行为定义得好吗?
https://stackoverflow.com/questions/55867320
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