41.内存函数实现(memcpy,memset,memmove,memicmp,memchr.memccpy)

1 #include <stdio.h>
2 #include <stdlib.h>
3 #include <memory.h>
4
5 void * mymemcpy(void* _Dst, void const* _Src, size_t _Size)
6 {
7     if (_Dst == NULL || _Src == NULL)
8     {
9         return NULL;
10     }
11
12     //转化成char类型,一次前进一个字节
13     char *dst = _Dst;
14     char *src = _Src;
15
16     for (int i = 0; i < _Size; i++)
17     {
18         dst[i] = src[i];
19     }
20
21     return _Dst;
22 }
23
24 void main()
25 {
26     int a[10] = { 1,2,3,4,5,6,7,8,9,10 };
27     int *p = malloc(sizeof(int) * 10);
28     int *tmp = mymemcpy(p, a, 40);
29
30     for (int i = 0; i < 10; i++)
31     {
32         printf("%d\n" ,p[i]);
33     }
34
35     char str[100] = "hello world";
36     char mystr[100];
37     mymemcpy(mystr, str, strlen(str) + 1);
38
39     printf("%s\n", mystr);
40
41     system("pause");
42 }

1 void *mymemset(void *_Dst, int _Val, size_t _Size)
2 {
3     if (_Dst == NULL || _Val == NULL)
4     {
5         return;
6     }
7
8     for (int i = 0; i < _Size; i++)
9     {
10         ((char *)_Dst)[i] = _Val;
11     }
12
13     return _Dst;
14 }

1 void * mymemmove(void *_Dst, const void *_Src, size_t _Size)
2 {
3     if (_Dst == NULL || _Src == NULL)
4     {
5         return NULL;
6     }
7
8     void *psrc = malloc(_Size);//分配内存
9     memcpy(psrc, _Src, _Size);
10     memcpy(_Dst, psrc, _Size);
11     free(psrc);
12     return _Dst;
13 }

1 int mymemicmp(const void *_Buf1, const void *_Buf2, size_t _Size)
2 {
3     //保存变量
4     char *buf1 = _Buf1;
5     char *buf2 = _Buf2;
6
7     //结束标识
8     char *end = buf1 + _Size;
9
10     while ((*buf1 == *buf2) && buf1 != end)
11     {
12         buf1++;
13         buf2++;
14     }
15
16     if (buf1 == end)
17     {
18         return 0;
19     }
20     else
21     {
22         return *buf1 - *buf2 > 0 ? 1 : -1;
23     }
24 }

1 void *mymemchr(void *start, char ch, int maxlength)
2 {
3     char *p = NULL;
4     for (int i = 0; i < maxlength; i++)
5     {
6         if (((char *)start)[i] == ch)
7         {
8             p = (char *)start + i;
9             break;
10         }
11     }
12     return p;
13 }

1 void * mymemccpy(void * _Dst, const void *_Src, int _Val,size_t _MaxCount)
2 {
3     char *dst = _Dst;
4     char *src = _Src;
5
6     for (int i = 0; i < _MaxCount; i++)
7     {
8         dst[i] = src[i];
9         if (dst[i] == _Val)
10         {
11             break;
12         }
13     }
14 }