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十二、C语言：内存函数

article 2025/3/19 6:37:59

一、memcpy

1.1 使用

void * memcpy ( void * destination, const void * source, size_t num );

1.前两个参数类型都是void*，因此可以拷贝任何数据类型；

2.num参数为要拷贝的字节数；

int main()
{
    char arr[10] = "abcdef";
    char brr[20] = {'\0'};
    int arr_int[10] = {0,1,2,3,4,5,6,7,8,9};
    int brr_int[10] = {0};
    memcpy(brr, arr, 3);
    memcpy(brr_int, arr_int, 4*5);  //拷贝前5个，共20字节
    printf("%s", brr);
    return 0;
}

1.2 模拟实现

void* my_memcpy(void* dest, void* src, size_t num)
{
    assert(dest && src);
    void* ret = dest;
    while (num--)
    {
        *(char*)dest = *(char*)src;
        dest = (char*)dest + 1;
        src = (char*)src + 1;
    }
    return ret;
}

二、memmove

2.1 使用

void * memmove( void * destination, const void * source, size_t num );

int main()
{
    int arr_int[10] = {1,2,3,4,5,6,7,8,9,10};
    int brr_int[10] = {0};
    memmove(arr_int+2, arr_int, 20);
    for (int i = 0; i < 10; i++)
        printf("%d ",arr_int[i]);  //1 2 1 2 3 4 5 8 9 10
    return 0;
}

2.2 模拟实现

void* my_memmove(void* dest, void* src, size_t num)
{
    void* ret = dest;
    if(dest > src)
    {
        while (num--)
        {
            *((char*)dest + num) = *((char*)src + num);
        }
    }
    else
    {
        while (num--)
        {
            *(char*)dest = *(char*)src;
            dest = (char*)dest + 1;
            src = (char*)src + 1;
        }
    }
    return ret;
}
int main()
{
    int arr_int[10] = {1,2,3,4,5,6,7,8,9,10};
    int brr_int[10] = { 1,2,3,4,5,6,7,8,9,10 };
    my_memmove(arr_int, arr_int+2, 20);      //从前向后拷贝
    my_memmove(brr_int + 2, brr_int, 20);    //从后向前拷贝
    for (int i = 0; i < 10; i++) 
        printf("%d ",brr_int[i]);
    return 0;
}

三、memcmp

int memcmp ( const void * ptr1, const void * ptr2, size_t num );

int main()
{
    float arr1[] = {1.0,2.0,3.0,4.0};
    float arr2[] = { 1.0,3.0,4.0 };
    int ret1 = memcmp(arr1, arr2, 4);  //0
    int ret2 = memcmp(arr1, arr2, 8);  //-1
    int ret3 = memcmp(arr2,arr1, 8);   //1
    printf("%d\n%d\n%d\n", ret1,ret2,ret3);
    return 0;
}

四、memset

void * memset ( void * ptr, int value, size_t num );

int main()
{
    int arr[10] = {0};
    int brr[10] = {0};
    memset(arr, 1, 20);
    //01 01 01 01  
    //01 00 00 00
    for (int i = 0; i < 5; i++)
    {
        memset(brr+i, 1, 1);
    }
    return 0;
}