string函数的一些实现

  1 /*************************************************************************
  2     > File Name: test.cpp
  3  ************************************************************************/
  4 #include"stdlib.h"
  5 #include"stdio.h"
  6 #include"string.h"
  7 
  8 char *mystrcat(char *dest,const char *src)
  9 {
 10     char* temp = dest;
 11     while(*dest != '')
 12     {
 13         dest++;
 14     }
 15 
 16     while((*dest++ = *src++) != '');
 17 
 18     return temp;
 19 }
 20 char *mystrncat(char *dest,const char *src,size_t n)
 21 {
 22     
 23     char* temp = dest;
 24     while(*dest != '')
 25     {
 26         dest++;
 27     }
 28 
 29     while(n-->0 && (*dest++ = *src++) != '');
 30 
 31     return temp;
 32 }
 33 
 34 
 35 
 36 void* mymemset(void *s, int c, size_t n )
 37 {
 38     unsigned char uc = c;
 39     unsigned char *su = (unsigned char*)s;
 40     while(n-->0)
 41     {
 42         *su = uc;
 43         su++;
 44     }
 45 }
 46 
 47 int mystrlen(const char* str)
 48 {
 49     return *str?(mystrlen(++str)+1):0;
 50     /*
 51     const char* eos = str;
 52     while(*eos++);
 53     return (eos-str-1);
 54     */
 55 }
 56 
 57 void* mymemcpy(void*dst, const void* src,size_t size)
 58 {
 59     
 60     if(src==NULL || dst==NULL) return NULL;
 61     void* ret = dst;
 62     while(size--)
 63     {
 64         *(char*)dst = *(char*)src;
 65         dst = (char*)dst + 1;
 66         src = (char*)src + 1;
 67     }
 68     return ret;
 69 }
 70 
 71 void* mymemmove(void*dst, const void* src,size_t size)
 72 {
 73     if(src==NULL || dst==NULL) return NULL;
 74     char* psrc;
 75     char* pdst;
 76     //存在覆盖，自后向前进行拷贝
 77     if((src<dst) && (char*)src+size > (char*)dst)
 78     {
 79         psrc = (char*)src + size-1;
 80         pdst = (char*)dst + size-1;
 81         while(size--)
 82             *pdst-- = *psrc--;
 83     }
 84     else
 85     {
 86         psrc = (char*)src;
 87         pdst = (char*)dst;
 88         while(size--)
 89         {
 90             *pdst++ = *psrc++;
 91         }
 92     }
 93 }
 94 
 95 int mymemcmp(const void * ptr1, const void * ptr2, size_t num)
 96 {
 97     if(ptr1==NULL || ptr2==NULL || num<0) return 0;
 98 
 99     char* pch1 = (char*)ptr1;
100     char* pch2 = (char*)ptr2;
101 
102     while(num-- && *pch1++ == *pch2++);
103     return (pch1-pch2)<<8;
104 }
105 
106 int mystrcmp ( const char * str1, const char * str2 )
107 {
108     if(str1==NULL || str2 ==NULL) return 0;
109 
110     while(*str1 == *str2)
111     {
112         str1++;
113         str2++;
114     }
115 
116     return (*str1-*str2);
117 }
118 
119 int mystrncmp( const char * str1, const char * str2, size_t num )
120 {
121 
122     if(str1==NULL || str2 ==NULL) return 0;
123 
124     while(num-- && *str1 == *str2)
125     {
126         str1++;
127         str2++;
128     }
129 
130     return (*str1-*str2);
131 }
132 
133 int main()
134 {
135     char ch1[] = "hello";
136     char ch2[] = "herld";
137  //   printf("strcat : %s
", mystrncat(ch1,ch2,2));
138     
139     printf("%d
",mystrcmp(ch2,ch1));
140 
141     printf("%d
",mystrncmp(ch2,ch1,4));
142 
143 
144     return 0;
145 }