不使用库函数、自己编写的(strlen、strcpy、strcmp、strcat、memcmp、memcpy、memmove)

不使用库函数、自己编写的(strlen、strcpy、strcmp、strcat、memcmp、memcpy、memmove)

  1 //求字符串长度的函数
  2 int my_strlen(const char* pStr)
  3 {
  4 assert(pStr != NULL);
  5 int length = 0;
  6 while (*pStr++ != '\0') 
  7 {
  8 length++;
  9 }
 10 return length;
 11 }
 12 //字符串拷贝函数
 13 char* my_strcpy(char* strDest, const char* strSrc)
 14 {
 15 assert(strDest != NULL && strSrc != NULL);
 16 char* pDest = strDest; //保护参数
 17 const char* pSrc = strSrc;
 18 while (*pSrc != '\0')
 19 {
 20 *pDest++ = *pSrc++;
 21 }
 22 //*pDest = '\0';
 23 return strDest;
 24 }
 25 //字符串比较函数
 26 int my_strcmp(const char* strDest, const char* strSrc)
 27 {
 28 assert(strDest != NULL && strSrc != NULL);
 29 if (*strDest == '\0'&&*strSrc != '\0')
 30 {
 31 return 0;
 32 }
 33 const char* pDest = strDest;
 34 const char* pSrc = strSrc;
 35 int result = 0; //用于记录比较结果
 36 while (*pDest != '\0' || *pSrc != '\0')
 37 {
 38 if ((result = *pDest - *pSrc) != 0) 
 39 {
 40 break;
 41 }
 42 pDest++;
 43 pSrc++;
 44 }
 45 if (result > 0)
 46 {
 47 result = 1;
 48 }
 49 else if (result<0)
 50 {
 51 result = -1;
 52 }
 53 return result;
 54 }
 55 //字符串连接函数
 56 char* my_strcat(char* strDest, char* strSrc)
 57 {
 58 assert(strDest != NULL && strSrc != NULL);
 59 char* pDest = strDest;
 60 char* pSrc = strSrc;
 61 while(*pDest != '\0') 
 62 {
 63 pDest++;
 64 }
 65 while (*pSrc != '\0')
 66 {
 67 *pDest++ = *pSrc++;
 68 }
 69 *pDest = '\0';
 70 return strDest;
 71 }
 72 
 73 //内存比较函数
 74 int my_memcmp(void* src1, void* src2, int len)
 75 {
 76 assert(src1 != NULL && src2 != NULL);
 77 const char* pSrc1 = (char*)src1;
 78 const char* pSrc2 = (char*)src2;
 79 while (len-- > 0)
 80 {
 81 if (*pSrc1++ != *pSrc2++) 
 82 {
 83 return *pSrc1 < *pSrc2 ? -1 : 1;
 84 }
 85 }
 86 return 0; 
 87 }
 88 
 89 //内存拷贝函数
 90 void* my_memcpy(void* dest, const void* src, size_t count)
 91 {
 92 assert(dest != NULL && src != NULL);
 93 char* pDest = (char*)dest;
 94 const char* pSrc = (const char*)src;
 95 while (count-- > 0)
 96 {
 97 *pDest++ = *pSrc++;
 98 }
 99 return dest;
100 }
101 
102 //内存移动函数
103 void* my_memmove(void* dest, void* src, size_t count)
104 {
105 assert(dest != NULL && src != NULL);
106 char* pDest = (char*)dest;
107 const char* pSrc = (char*)src;
108      if (pSrc >= pDest || pDest >= (pSrc + count))
109 {
110 
111 
112     while (count-- > 0)
113         {
114              *pDest++ = *pSrc;
115        }
116 }
117 else
118  {
119       while (count-- > 0)
120 
121           {
122 
123               *(pDest + count) = *(pSrc + count);
124          }
125 }
126 *pDest = '\0';
127 return dest;
128 }

 

posted @ 2016-04-19 10:46  A_carat_tear  阅读(540)  评论(0编辑  收藏