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++ != ' ') 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 != ' ') 19 { 20 *pDest++ = *pSrc++; 21 } 22 //*pDest = ' '; 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 == ' '&&*strSrc != ' ') 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 != ' ' || *pSrc != ' ') 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 != ' ') 62 { 63 pDest++; 64 } 65 while (*pSrc != ' ') 66 { 67 *pDest++ = *pSrc++; 68 } 69 *pDest = ' '; 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 = ' '; 127 return dest; 128 }