《Windows核心编程》---C运行库的内存对齐函数

C运行库提供了一系列函数用于分配对齐过的内存：

1）_aligned_malloc函数的功能是分配一块对齐过的内存：

void * _aligned_malloc(

size_t size, //要分配的字节数

size_t alignment //要对齐到的字节边界，传给alignment的值必须是2的整数幂次方

);

2）_aligned_offset_malloc函数用于在指定的内存对齐边界上分配内存：

void * _aligned_offset_malloc(

size_t size, //要分配的字节数

size_t alignment, //要对齐到的字节边界，传给alignment的值必须是2的整数幂次方

size_t offset //为达到内存对齐所指定的偏移量

);

3）_aligned_realloc函数和_aligned_offset_realloc函数用于改变由_aligned_malloc或者_aligned_offset_malloc分配的内存的大小：

void * _aligned_realloc(

void *memblock, //要改变大小的内存地址

size_t size, //新分配的字节数

size_t alignment //要对齐到的字节边界，传给alignment的值必须是2的整数幂次方

);

void * _aligned_offset_realloc(

void *memblock,

size_t size,

size_t alignment,

size_t offset

);

4）_aligned_free函数用于释放由上述函数申请的内存资源：

void _aligned_free (

void *memblock

);

实例代码如下：

#include <iostream>

#include <malloc.h>

#include <stdio.h>

using namespace std;

int main()

{

void *ptr;

size_t alignment;

size_t offset;

//注意alignment必须是2的整数幂次方

alignment = 16;

offset = 5;

//使用_aligned_malloc

ptr = _aligned_malloc(100, alignment);

if(ptr == NULL)

{

printf_s("Error allocation aligned memory/n");

return -1;

}

if(((int)ptr % alignment) == 0)

{

printf_s("This pointer, %d, is aligned on %d/n",

ptr, alignment);

}

else

{

printf_s("This pointer, %d, is not aligned on %d/n",

ptr, alignment);

}

//使用_aligned_realloc

ptr = _aligned_realloc(ptr, 200, alignment);

if(((int)ptr % alignment) == 0)

{

printf_s("This pointer, %d, is aligned on %d/n",

ptr, alignment);

}

else

{

printf_s("This pointer, %d, is not aligned on %d/n",

ptr, alignment);

}

//释放

_aligned_free(ptr);

//使用_aligned_offset_malloc

ptr = _aligned_offset_malloc(200, alignment, offset);

if(ptr == NULL)

{

printf_s("Error allocation aligned offset memory/n");

return -1;

}

if((((int)ptr + offset) % alignment) == 0)

{

printf_s("This pointer, %d, is offset by %d on alignment of %d/n",

ptr, offset, alignment);

}

else

{

printf_s("This pointer, %d, does not satisfy offset %d and alignment %d/n",

ptr, offset, alignment);

}

//使用_aligned_offset_realloc

ptr = _aligned_offset_realloc(ptr, 200, alignment, offset);

if(ptr == NULL)

{

printf_s("Error reallocation aligned offset memory/n");

return -1;

}

if((((int)ptr + offset) % alignment) == 0)

{

printf_s("This pointer, %d, is offset by %d on alignment of %d/n",

ptr, offset, alignment);

}

else

{

printf_s("This pointer, %d, does not satisfy offset %d and alignment %d/n",

ptr, offset, alignment);

}

//_aligned_free同时与_aligned_malloc和_aligned_realloc配合使用

_aligned_free(ptr);

system("pause");

return 0;

}