strcpy,strcat,strstr,strcmp,memmove的实现

1.实现strcpy

把从src地址开始且含有''结束符的字符串复制到以dest开始的地址空间

#include <stdio.h>
#include <Windows.h>
#include <assert.h>
char* my_strcpy(char* dest, const char* src)
{
assert(dest != NULL);
assert(src != NULL);
char* start = dest;
while (*dest = *src)
{
dest++;
src++;
}
return start;
}
int main()
{
char arr1[] = "hello";
char arr2[] = "world";
my_strcpy(arr1, arr2);
printf("%sn", arr1);
system("pause");
return 0;
}

2.strcat

用于连接两个字符串

#include <stdio.h>
#include <assert.h>
#include <Windows.h>
char* my_strcat(char* dest, const char* src)
{
assert(dest);
assert(src);
char* temp = dest;
while (*dest)
dest++;
while (*dest++ = *src++)
{
;
}
return temp;
}
int main()
{
char arr1[] = "hello ";
char arr2[] = "world";
my_strcat(arr1, arr2);
printf("%s", arr1);
system("pause");
return 0;
}

3.strstr

strstr(dest,src) 函数用于判断字符串src是否是dest的子串。如果是，则该函数返回src在dest中首次出现的地址；否则，返回NULL。

#include <stdio.h>
#include <Windows.h>
#include <assert.h>
char* my_strstr(const char* dest, const char* src)
{
assert(dest);
assert(src);
const char* cur = dest;
while (*cur)
{
const char* s1 = cur;
const char* s2 = src;
while ((*s1) && (*s2) && (*s1 == *s2))
{
s1++;
s2++;
}
if (*s2 == '')
{
return (char*)cur;
}
cur++;
}
return NULL;
}
int main()
{
char arr1[] = "hello ";
char arr2[] = "world";
char* ret = my_strstr(arr1, "l");
if (ret == NULL)
{
printf("non");
}
else
{
printf("%sn", ret);
}
system("pause");
return 0;
}

4.strcmp

strcmp用于比较两个字符串s1和s2，若s1>s2,返回1; s1==s2,返回0；若s1<s2,返回-1；

#include <stdio.h>
#include <Windows.h>
#include <assert.h>
int my_strcmp(const char*s1, const char* s2)
{
assert(s1);
assert(s2);
while (*s1 == *s2)
{
if (*s1 == '')
return 0;
s1++;
s2++;
}
if (*s1 > *s2)
return 1;
else
return -1;
}
int main()
{
char arr1[] = "hello ";
char arr2[] = "world";
int ret = my_strcmp(arr1, arr2);
printf("%dn", ret);
system("pause");
return 0;
}

5.memmove

memmove用于从src拷贝count个字节到dest，如果目标区域和源区域有重叠的话，memmove能够保证源串在被覆盖之前将重叠区域的字节拷贝到目标区域中。但复制后src内容会被更改。但是当目标区域与源区域没有重叠则和memcpy函数功能相同。

#include <stdio.h>
#include <Windows.h>
#include <assert.h>
void* my_memmove(const void* dest, const void* src,int count)
{
assert(dest);
assert(src);
char* cur = (char*)dest;
while (*cur)
{
char* pdest = (char*)dest;
char* psrc = (char*)src;
if ((pdest > psrc) && (pdest < psrc + count))
{
while (count--)
*(pdest+count) = *(psrc+count);
}
else
{
while (count--)
{
*pdest = *psrc;
}
}
cur++;
}
return dest;
}
int main()
{
int arr1[20] = { 1,2,3,4,5,6,7,8,9,0 };
int arr2[10] = { 0 };
my_memmove(arr1 + 3, arr1, 20);
system("pause");
return 0;
}

如发现错误，请及时告知我谢谢~

最后

以上就是舒心发箍最近收集整理的关于strcpy,strcat,strstr,strcmp,memmove的实现的全部内容，更多相关strcpy,strcat,strstr,strcmp,memmove内容请搜索靠谱客的其他文章。