字符函数串讲

最新推荐文章于 2021-03-24 01:02:00 发布

原创最新推荐文章于 2021-03-24 01:02:00 发布 · 247 阅读

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CC 4.0 BY-SA版权

本文模拟实现了几个常用的字符串操作函数，包括strncpy、strncat、strncmp及strrstr等，并提供了详细的代码示例。通过这些模拟实现，读者可以更好地理解这些函数的工作原理。

1.模拟实现
strncpy

#include<stdio.h>
#include<assert.h>
#include<iostream>
char*my_strncpy(char*dest, const char*src, int n)
{
assert(dest != NULL);
assert(src != NULL);
int i = 0;
char *tmp = dest;
while ((i++<n) && (*tmp++ = *src++) != '\0')
{
;
}
return dest;
}

int main()
{
char str1[] = "1234567890";
char str2[] = "abcde";
my_strncpy(str1, str2, 6);
printf("%s\n", str1);
system("pause");
return 0;
}

strncat

#include<stdio.h>
#include<assert.h>
#include<iostream>
char*my_strncat(const char*src, char*dest, int n)
{
assert(src != NULL&&dest != NULL);
char*tmp = dest;
while (*tmp != '\0')
{
tmp++;
}
while ((n--) && (*tmp++ = *src++) != '\0')
{
;
}
return dest;

}
int main()
{
char str1[20] = "hello ";
char str2[6] = "word!";
my_strncat(str2, str1, 2);
printf("%s\n", str1);
system("pause");
return 0;
}

strncmp

#include<stdio.h>
#include<iostream>
#include<assert.h>
int my_strncmp(const char*str1, const char*str2, int n)
{
assert(str1 != NULL);
assert(str2 != NULL);
while ((*str1 != '\0') && (*str2 != '\0') && n)
{
  if ((*str1 - *str2) > 0)
   return 1;
  if ((*str1 - *str2)<0)
   return -1;
  str1++;
  str2++;
  n--;
}
if (*str1 == '\0'&&*str2 != '\0')
  return -1;
if (*str1 != '\0'&&*str2 == '\0')
  return 1;
return 0;
}
int main()
{
char str1[] = "abcdef";
char str2[] = "abcmln";
int ret = my_strncmp(str1, str2, 4);
printf("%d\n", ret);
system("pause");
return 0;
}
2.模拟实现
strrstr

#include<stdio.h>
#include<assert.h>
#include<iostream>
char*my_strrstr(char*str1, char*str2)
{
assert(str1 != NULL&&str2 != NULL);
int i = 0;
int j = 0;
char*ret = 0;
for (i = 0; str1[i] != 0; i++)
{
  for (j = 0; str2[j] != 0; j++)
  {
   if (str1[i + j] != str2[j])
   {
    break;
   }
  }
  if (str2[j] == 0)
   ret = str1 + i;

}
return ret;
}

int main()
{
char str[] = "abbcdbcdefmln";
char str1[] = "bcd";
//char *tmp=my_strstr(str, str1);
printf("%s", my_strrstr(str, str1));
system("pause");
return 0;
}

strchr

#include <stdio.h>
char const * my_strchr(char const *str, char ch)
{
while (*str != '\0')//判断str是否已经查找到最后一个字符
{
  if (ch == *str)//当在str中第一次找到ch就返回ch
  {
   return str;
  }
  str++;
}
return NULL;//当str中没有ch时就返回null
}
int main()
{
char const * my_strchr(char const *str, char ch);
char str[] = "asfdgdhjjk";
char ch = 'd';
printf("%s\n", my_strchr(str, ch));
return 0;
}