如何在此 C 代码中释放所有动态分配的内存实例

Question

我已经编写了这个 C 代码。一开始，我使用文件处理来读取文本文件并将每一行作为字符串插入到链表中。我需要在一个单独的 void 函数中释放程序中所有的内存分配情况。我怎么做？我只包含了相关的代码部分，因为它是一个相当长的程序。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <stdbool.h>
#include <ctype.h>



/*Node of linked list*/
typedef struct node {
    char *data;
    struct node *next;
} node;

node *start = NULL;
node *current;

typedef enum {
    not_tested, found, missed
} state;

/*Appending nodes to linked list*/
void add(char *line) {

    node *temp = (node *)malloc(sizeof(node));
    temp->data = strdup(line);
    temp->next = NULL;
    current = start;

    if (start == NULL) {
        start = temp;
    }
    else {
        while (current->next != NULL) {
            current = current->next;
        }
        current->next = temp;
    }
}

/*read text file*/
void readfile(char *filename) {
    FILE *file = fopen(filename, "r");

    if (file == NULL) {
        exit(1);
    }

    char buffer[512];

    while (fgets(buffer, sizeof(buffer), file) != NULL) {
        add(buffer);
    }

    fclose(file);
}

Answer 1

这并不完全符合您的要求，但我将向您展示如何构建一个小类来分配可以在一次调用中释放的内存块。当您有大量小块内存要分配并因此在使用后释放时，这尤其有用。

对于您的使用而言，代码似乎太多了，但请注意，这样的类可以保存在一个独立的文件中，并在每次需要时重复使用：

struct Allocator {
    void * buffer;
    size_t capacity;
    size_t usedSize;
};

struct Allocator * newAllocator(size_t initialSize) {
    struct Allocator * allocator = malloc(sizeof(*allocator));
    if (! allocator) return NULL;
    allocator->buffer = malloc(initialSize);
    if (! allocator->buffer) { free(allocator); return NULL; }
    allocator->capacity = initialSize;
    allocator->usedSize = 0;
    return allocator;
}

void freeAllocator(struct Allocator * allocator) {
    if (!allocator) return;
    if (allocator->buffer) free(allocator->buffer);
    free(allocator);
}

void * allocate(struct Allocator * allocator, size_t size) {
    if (size + allocator->usedSize > allocator->capacity) {
        while (size + allocator->usedSize > allocator->capacity) allocator->capacity *= 2;
        allocator->buffer = realloc(allocator->buffer, allocator->capacity);
    }
    void * ptr = allocator->buffer + allocator->usedSize;
    allocator->usedSize += size;
    return ptr;
}
//-------- END ALLOCATOR

struct node {
    //...
};

// How to replace a call to malloc to allocate a node :
void add(struct Allocator *allocator, char *line) {
     struct node *temp = allocate(allocator, sizeof(*temp));
    //...
}

int main()
{
    FILE *file = fopen("myfileName", "r");
    if (file == NULL) exit(1);
    
    // Allocates the buffer and as many nodes as needed 
    struct Allocator *allocator = newAllocator(1024);
    char * buffer = allocate(allocator, 512);
    while (fgets(buffer, 512, file) != NULL) {
        add(allocator, buffer);
    }
    // Free all allocated memory in a single call
    freeAllocator(allocator);
    return 0;
}