最近是校招很热的季节，实验室里讨论最多的也就是算法，面试和笔试的必备知识储备。昨天想起 C 语言中 string.h 中的函数在操作字符串时很方便，所以，就想起写写那些函数。
当然，这些函数实现的只是简单的功能，并没有加入太多的排错功能，欢迎大家及时指正代码中出现的问题，谢谢！
my_string.h
#include <stdio.h>
#include <stdlib.h>
int my_strcmp(char *string1, char *string2);
int my_strlen(char *string);
char *my_strcat(char *res, const char *string);
char *my_strcpy(const char *sou, char *dest);
const char *my_strchr(char const *str,int ch);
const char *my_strstr(char const *s1,char const *s2);
my_string.c
#include <stdio.h>
#include <stdlib.h>
#include "my_string.h"
int my_strcmp(char *string1, char *string2)
{
char *index1 = string1;
char *index2 = string2;
while (*index1 == *index2 && *index1 != '\0' && *index2 != '\0')
{
index1++;
index2++;
}
if (*index1 - *index2 > 0)
{
return 1;
}
else if (*index1 - *index2 < 0)
{
return -1;
}
else
{
return 0;
}
}
int my_strlen(char *string)
{
char *temp = string;
int count = 0;
if (string == NULL || *string == '\0')
{
return 0;
}
while (*temp != '\0')
{
temp++;
count++;
}
return count;
}
char *my_strcat(char *res, const char *string)
{
char *ret = res;
if (string == NULL || *string == '\0')
{
return res;
}
while (*res != '\0')
{
res++;
}
while (*string != '\0')
{
*res++ = *string++;
}
*res = '\0';
return ret;
}
char *my_strcpy(const char *sou, char *dest)
{
char *addr = dest;
if (dest == NULL || sou == NULL)
{
return NULL;
}
while (*sou != '\0')
{
*dest++ = *sou++;
}
*dest = '\0';
return addr;
}
const char *my_strchr(char const *str,int ch)
{
if (str == NULL || *str == '\0')
{
return NULL;
}
while (*str != ch && *str != '\0')
str++;
if (*str == ch)
return str;
else
return NULL;
}
/*************************************************/
const char *my_strstr(char const *s1,char const *s2)
{
int n;
if (*s2 == '\0' || s2 == NULL)
{
return s1;
}
while (*s1 != '\0')
{
for (n = 0; *(s1 + n) == *(s2 + n); n++)
{
if (*(s2 + n + 1) == '\0')
return s1;
}
s1++;
}
return NULL;
}
/*************************************************/
