C实现字符操作函数，strcpy, strcat, strcmp, memcpy

1. char *strcpy(char *strDest, const char *strSrc)
2. {
3.     assert((strDest!=NULL) && (strSrc !=NULL));
4.     char *address = strDest;
5.     while( (*strDest++ = * strSrc++) != '\0' ) 
6. NULL;
7. return address;
8. }

1. char* strcat(char *str1,char *str2)  
2. {
3.  asser((str!=NULL) && (str2!=NULL));
4.  char* tempt = str1;  
5. 
6.  while(*str1++!='\0')   
7. 
8.  while(*str2!='\0')  
9.  {  
10.     *str1++ = *str2++;
11.   }  
12.   *str1 = '\0';  
13. 
14.   return tempt;  
15. }

1. int strcmp(const char* str1, const char* str2)  
2. {  
3.  assert((str1 != NULL) && (str2 != NULL);  
4.  int ret = 0;  
5.  while (!(ret = (unsigned char*)*str1 - (unsigned char*)*str2) && (*str2))  
6.  {  
7.    str1++;  
8.    str2++;  
9.  }  
10.   if(ret > 0)  
11.   {  
12.     return 1;  
13.   }  
14.   else if (ret < 0)  
15.   {  
16.     return -1
17.   } 
18. 
19.   return 0;  
20. }

1. void* memcpy(void *dest , const void* src , size_t count)    
2. {    
3.     assert( (dest != NULL) && (src != NULL));     //安全检查    
4.     assert(count > 0);
5.     char* psrc = (char *)src;
6.     char* pdest = (char *)dest;
7.     while(count--)    
8.     { 
9. *pdest++ = *psrc++;    
10.     } 
11. return dest; 
12. }