c++的c风格字符串函数的实现

　　要注意使用断言判断传入的字符串非空。

 #include <cassert>

 //求字符串长度
 size_t StrLen(const char *str)
 {
     assert(str != nullptr);
     size_t len = ;
     while (*str++ != '\0')
     {
         ++len;
     }
     return len;
 }

 //复制字符串
 char* StrCpy(char *dest, const char *src)
 {
     assert(dest != nullptr && src != nullptr);
     char *temp = dest;
     while ((*dest++ = *src++) != '\0');
     return temp;
 }

 //复制指定长度字符串
 char* StrNCpy(char *dest, const char *src, size_t n)
 {
     assert(dest != nullptr && src != nullptr);
     char *temp = dest;
     size_t i = ;
     while (i++ < n && (*dest++ = *src++) != '\0');
     if (*dest != '\0')
     {
         *dest = '\0';
     }
     return temp;
 }

 //比较字符串
 int StrCmp(const char *lhs, const char *rhs)
 {
     assert(lhs != nullptr && rhs != nullptr);
     int ret = ;
     while (!(ret = *(const unsigned char *)lhs - *(const unsigned char *)rhs) && *rhs)
     {
         ++lhs;
         ++rhs;
     }
     if (ret > )
     {
         return ;
     }
     else if (ret < )
     {
         return -;
     }
     else
     {
         return ;
     }
 }

 //拼接字符串
 char* StrCat(char *dest, const char *src)
 {
     assert(dest != nullptr && src != nullptr);
     char *temp = dest;
     while (*dest != '\0')
     {
         ++dest;
     }
     while ((*dest++ = *src++) != '\0');
     return temp;
 }

 //附：实现memcpy()函数
 void* MemCpy(void *dest, const void *src, size_t n)
 {
     assert(dest != nullptr && src != nullptr);
     //不可直接对void类型的指针进行操作
     char *temp_dest = (char*)dest;
     const char *temp_src = (char*)src;
     while (n--)
     {
         *temp_dest++ = *temp_src++;
     }
     return dest;
 }

 //附2：实现memset()函数
 void* MemSet(void *buffer, int c, size_t n)
 {
     assert(buffer != nullptr);
     char *temp = (char*)buffer;
     while (n--)
     {
         *temp++ = (char)c;
     }
     return buffer;
 }