使用结构的2D内存分配
使用结构的2D内存分配
提问于 2021-07-27 06:07:41
//我必须创建一个新的imgr_t，其中包含初始大小行、cols和它们的保留对应项(行和reserved_rows将是相同的，而cols和reserved_cols是相同的)。如果分配成功(即内存分配成功)，则返回指向新分配的imgr_t的指针，如果不成功，则返回空指针。
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
/* Structure type that encapsulates image: 2D array.
* the rows represent the indices of the main array,
* the cols represent the indices of the arrays pointed to by the pointers
* in the elements of the main array.
*/
typedef struct {
uint8_t** pixels;
unsigned int rows;
unsigned int cols;
unsigned int reserved_rows;
unsigned int reserved_cols;
} imgr_t;
/***** I am thinking something is wrong here but I cannot figure out what *****/
imgr_t* imgr_create(unsigned int rows, unsigned int cols){
imgr_t* arr;
arr->rows = rows;
arr->cols = cols;
arr->reserved_rows = rows;
arr->reserved_cols = cols;
arr = malloc(rows*sizeof(imgr_t));
for(int i = 0; i<arr->rows; i++){
arr->pixels[i] = malloc(cols*sizeof(imgr_t));
}return arr;
}
void imgr_destroy(imgr_t* im){
if(im != NULL){
free(im->pixels);
free(im);
}
}
// helper function that prints the content of the img
void print_img(imgr_t* im) {
if (im == NULL) {
printf("Invalid img (null).\n");
return;
}
printf("Printing img of row length %d and col length %d:\n", im->rows, im->cols);
for (unsigned int i=0; i<im->rows; i++) {
for (unsigned int j=0; j<im->cols; j++) {
printf("%d ", im->pixels[i][j]);
}
printf("\n");
}
printf("\n");
}
int main(){
imgr_t* test_im;
printf("Creating test_im by calling 'img_create(10, 10)'\n");
test_im = imgr_create(10, 10);
printf("test_im created successfully.\n\n");
return 0;
}
/*
Output what I am getting : Creating test_im by calling 'img_create(10, 10)'
signal: segmentation fault (core dumped)
*/回答 2
Stack Overflow用户
回答已采纳
发布于 2021-07-27 08:27:54
规则是需要调用free的次数与ons调用malloc的次数相同。uint8_t** pixels;不是指向2D数组的指针，而是指向数组指针的指针，因此您需要两次传递分配(在free时间相同)。
在这里你需要：
- 1为
imgr_t结构分配 - 1为指向行的指针数组分配
- 1每行(*)
代码可以是：
imgr_t* imgr_create(unsigned int rows, unsigned int cols) {
imgr_t* arr = malloc(sizeof *arr);
if (NULL == arr) return arr; // do not forget to test allocation!
arr->rows = rows;
arr->cols = cols;
arr->reserved_rows = rows;
arr->reserved_cols = cols;
arr->pixels = malloc(rows * sizeof(*arr->pixels)); // allocate rows
if (NULL == arr->pixels) { // another allocation to test
free(arr);
return NULL;
}
for (unsigned int i = 0; i < arr->rows; i++) {
arr->pixels[i] = malloc(cols * sizeof(uint8_t));
if (NULL == arr->pixels[i]) { // free what was allocated so far
for (int j = 0; j < i; j++) {
free(arr->pixels[i]);
}
free(arr->pixels)
free(arr);
return NULL;
}
}return arr;
}
void imgr_destroy(imgr_t* im) {
if (im != NULL) {
// one free per malloc...
for (unsigned int i = 0; i < im->rows; i++) {
free(im->pixels[i]);
}
free(im->pixels);
free(im);
}
}小心:我不明白什么是保留，所以我忽略了它.
(*)实际上，可以在一次传递中分配整个数组，然后让指向行的指针指向全局数组中每一行的开始，但这是一种高级方法.
Stack Overflow用户
发布于 2021-07-27 06:10:01
imgr_t* imgr_create(unsigned int rows, unsigned int cols){
imgr_t* arr;
arr->rows = rows;
arr->cols = cols;
arr->reserved_rows = rows;
arr->reserved_cols = cols;
arr = malloc(rows*sizeof(imgr_t));
for(int i = 0; i<arr->rows; i++){
arr->pixels[i] = malloc(cols*sizeof(imgr_t));
}return arr;
}在这里，您在初始化arr之前使用它。您的初始化似乎是错误的，因为您只需要分配一个imgr_t元素。像素初始化在我看来也是错误的:类型不正确，您需要使用uint8_t类型。您还需要分配一些空间来存储像素：
imgr_t* imgr_create(unsigned int rows, unsigned int cols){
imgr_t* arr = malloc(sizeof(imgr_t));
arr->rows = rows;
arr->cols = cols;
arr->reserved_rows = rows;
arr->reserved_cols = cols;
arr->pixels = malloc(rows * sizeof(uint8_t*));
for(int i = 0; i<arr->rows; i++){
arr->pixels[i] = malloc(cols*sizeof(uint8_t));
}
return arr;
}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/68539743
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