我将分享Malloc和free的完整方法,它适用于每种情况。这是使用数组进行补充的。我们也可以使用链接列表来实现元数据。
有三种场景需要覆盖:
1. 连续内存分配:以连续方式分配内存。
2. 在两个已分配的内存之间分配内存:当内存在两个已分配的内存块之间可用时,我们必须使用该内存块进行分配。
3. 从初始块分配内存时,初始块是空闲的。
详见下图:
内存分配算法的分配图
malloc源代码:
#define TRUE 1
#define FALSE 0
#define MAX_ALOCATION_ALLOWED 20
static unsigned char our_memory[1024 * 1024];
static int g_allocted_number = 0;
static int g_heap_base_address = 0;
typedef struct malloc_info
{
int address;
int size;
}malloc_info_t;
malloc_info_t metadata_info[MAX_ALOCATION_ALLOWED] ={0};
void* my_malloc(int size)
{
int j =0;
int index = 0 ;
int initial_gap =0;
int gap =0;
int flag = FALSE;
int initial_flag = FALSE;
void *address = NULL;
int heap_index = 0;
malloc_info_t temp_info = {0};
if(g_allocted_number >= MAX_ALOCATION_ALLOWED)
{
return NULL;
}
for(index = 0; index < g_allocted_number; index++)
{
if(metadata_info[index+1].address != 0 )
{
initial_gap = metadata_info[0].address - g_heap_base_address;
if(initial_gap >= size)
{
initial_flag = TRUE;
break;
}
else
{
gap = metadata_info[index+1].address - (metadata_info[index].address + metadata_info[index].size);
if(gap >= size)
{
flag = TRUE;
break;
}
}
}
}
if(flag == TRUE)
{
heap_index = ((metadata_info[index].address + metadata_info[index].size) - g_heap_base_address);
for(j = MAX_ALOCATION_ALLOWED -1; j > index+1; j--)
{
memcpy(&metadata_info[j], &metadata_info[j-1], sizeof(malloc_info_t));
}
}
else if (initial_flag == TRUE)
{
heap_index = 0;
for(j = MAX_ALOCATION_ALLOWED -1; j > index+1; j--)
{
memcpy(&metadata_info[j], &metadata_info[j-1], sizeof(malloc_info_t));
}
}
else
{
if(g_allocted_number != 0)
{
heap_index = ((metadata_info[index -1].address + metadata_info[index-1].size) - g_heap_base_address);
}
else
heap_index = 0;
}
address = &our_memory[heap_index];
metadata_info[index].address = g_heap_base_address + heap_index;
metadata_info[index].size = size;
g_allocted_number += 1;
return address;
}
现在免费编写代码。
void my_free(int address)
{
int i =0;
int copy_meta_data = FALSE;
for(i = 0; i < g_allocted_number; i++)
{
if(address == metadata_info[i].address)
{
g_allocted_number -= 1;
copy_meta_data = TRUE;
printf("g_allocted_number in free = %d %d\n", g_allocted_number, address);
break;
}
}
if(copy_meta_data == TRUE)
{
if(i == MAX_ALOCATION_ALLOWED -1)
{
metadata_info[i].address = 0;
metadata_info[i].size = 0;
}
else
memcpy(&metadata_info[i], &metadata_info[i+1], sizeof(malloc_info_t));
}
}
现在进行测试的代码是:
int main()
{
int *ptr =NULL;
int *ptr1 =NULL;
int *ptr2 =NULL;
int *ptr3 =NULL;
int *ptr4 =NULL;
int *ptr5 =NULL;
int *ptr6 =NULL;
g_heap_base_address = &our_memory[0];
ptr = my_malloc(20);
ptr1 = my_malloc(20);
ptr2 = my_malloc(20);
my_free(ptr);
ptr3 = my_malloc(10);
ptr4 = my_malloc(20);
ptr5 = my_malloc(20);
ptr6 = my_malloc(10);
printf("Addresses are: %d, %d, %d, %d, %d, %d, %d\n", ptr, ptr1, ptr2, ptr3, ptr4, ptr5, ptr6);
return 0;
}