从文件中读取c中结构数组中的dma结构时如何分配内存答案

【问题标题】：How do you allocate memory when reading from a file for a dma struct in a struct array in c从文件中读取c中结构数组中的dma结构时如何分配内存
【发布时间】：2020-10-29 07:12:57
【问题描述】：

所以我有一个地图，它由一个结构数组组成，看起来像这样


//Header files
#include <string.h>
#include <stdlib.h>
#include <dirent.h>

//Symbolic names
#define mapSize 301

//This struct will be used to store item data in the map
struct mapItem
{
    char name[21];
    short id;
    short type;
    short amount;
}; //End mapItem

//This struct will be used for map generation and storage
struct tile
{
    char name[21];
    short id;
    char description[100];
    short itemAmount;
    struct mapItem *item;
}; //End tile struct

//This struct variable is the map
struct tile map[mapSize][mapSize];

//Function signatures
void itemGen();

int main()
{
    
    char str[4];
    FILE *characterF, *inventoryF, *mapF;

    itemGen();

    //Opens map file
    /*Example file path is C:\*/
    strcpy(str, "C:\");
    mapF = fopen(str, "w");

    //writes map to file
    fwrite(map, sizeof(struct tile), (mapSize*mapSize), mapF);

    //Closes file
    fclose(mapF);

    /*This would not usually be streight after the file had been written to
    //Opens file
    mapF = fopen(str, "w");

    

    //Reads from file
    fread(map, sizeof(struct tile), mapSize*mapSize, mapF);

    return 0;
} //End main


/*This is just an example in the actual program the itemAmount is not always 3*/
void itemGen()
{

    short x, y;
    x = y  = 100;

    //Sets value of itemAmount for example
    map[y][x].itemAmount = 3;

    //Allocates 3 structs in memory
    map[y][x].item = (struct mapItem *)calloc(map[y][x].itemAmount, sizeof(struct mapItem));

    //This will add 3 items to the tile
    strcpy((map[y][x].item+0)->name, "Apple");
    strcpy((map[y][x].item+1)->name, "Bag");
strcpy((map[y][x].item+1)->name, "Bag");

} //End itemGen

一旦我开始读取文件部分，似乎我需要为将存储在图块中的项目声明内存。因为这不是我在代码中提到的固定数字，我该如何处理？

欢迎使用此过程的任何替代方法。谢谢！

【问题讨论】：

文件中存储的数据结构不应该有指针。不要将struct mapItem *item 成员存储在文件中，而是存储item[0]、item[1]、...、item[itemAmount-1] 元素。一个术语是“扁平化”数据，也称为“序列化”数据。

标签： c windows gcc io dma

【解决方案1】：

地图数据写入文件时需要序列化，从文件中读回时需要反序列化。一种方法是：

for (int y = 0; y < mapSize; y++) {
    for (int x = 0; x < mapSize; y++) {
        fwrite(&map[y][x], offsetof(struct tile, item), 1, mapF);
        fwrite(map[y][x].item, sizeof(struct mapItem), map[y][x].itemAmount, mapF);
    }
}

为清楚起见，省略了错误检查。

读取类似于写入，但需要分配内存：

for (int y = 0; y < mapSize; y++) {
    for (int x = 0; x < mapSize; y++) {
        fread(&map[y][x], offsetof(struct tile, item), 1, mapF);
        map[y][x].item = calloc(map[y][x].itemAmount, sizeof(struct mapItem));
        fread(map[y][x].item, sizeof(struct mapItem), map[y][x].itemAmount, mapF);
    }
}

为了清楚起见，再次省略了错误检查。

【讨论】：