一些字符串操作函数的模拟实现

最新推荐文章于 2024-08-10 23:29:05 发布

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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,strncmp,strncat,strstr,strrstr,strchr和strrchr。通过这些函数的实现过程，帮助读者更好地理解字符串操作的基本原理。

下面我们模拟实现一下几个字符串操作的函数。

模拟实现strncpy:

#include<stdio.h>
#include<assert.h>
#include<stdlib.h>

char *my_strncpy(char *dest, char *src, size_t n)
{
	assert(dest != NULL);
	assert(src != NULL);
	char *p = dest;
	while (n)
	{
		*dest = *src;
		dest++;
		src++;
		n--;
	}
	return p;
}

int main(void)
{
	char buf1[100] = "heelo";
	char buf2[100] = "world";
	printf("%s\n", my_strncpy(buf2, buf1, 4));
	system("pause");
	return 0;
}

模拟实现strncmp:

#include<stdio.h>
#include<assert.h>
#include<stdlib.h>
int my_strncmp(const char *dest, const char *src, size_t count)
{
	assert(dest != NULL);
	assert(src != NULL);
	while (count--)
	{
		if ((*dest - *src) > 0)
		{
			return 1;
		}
		else if ((*dest - *src) < 0)
		{
			return -1;
		}
		else
		{
			;
		}
		*dest++;
		*src++;
	}
	return 0;
}
int main()
{
	char arr[] = "zhangsan";
	char arr1[] = "zhangsi";
	int ret = my_strncmp(arr, arr1, 8);
	printf("ret = %d", ret);
	system("pause");
	return 0;
}

模拟实现strncat:

#include<stdio.h>
#include<stdlib.h>
#include<assert.h>
#include<string.h>
char* my_strncat(char *dest, const char *src,size_t count)
{
	assert(dest != NULL);
	assert(src != NULL);
	char *tmp = dest;
	while (*dest != '\0')
	{
		*dest++;
	}
	while (count && (*dest++ = *src++))
	{
		if (*src == '\0')
		{
			*dest = *src;
			break;
		}
		else
		{
			count--;
		}
	}
	return tmp;
}
int main()
{
	char arr[20] = "hello";
	char arr1[] = "world";
	char *tmp = my_strncat(arr, arr1, 2);
	printf("%s\n", tmp);
	printf("%d", strlen(tmp));//测试下有没有把\0连接到arr里
	system("pause");
	return 0;
}

模拟实现strstr：

#include<stdio.h>
#include<stdlib.h>
char* my_strstr(const char *dest, const char *src)
{
	const char *cp = dest;
	const char *p = src;
	const char *start = NULL;
	while(*cp)
	{
		start = cp;
		while(*cp && *p && *cp == *p)
		{
			cp++;
			p++;
		}
		if(*p == '\0')
		{
			return (char *)start;
		}
		cp = start+1;
		p = src;
	}
	return NULL;
}
int main()
{
	char arr[] = "abcdefgbcd";
	char arr1[] = "bcd";
	char *tmp = my_strstr(arr, arr1);
	if(tmp == NULL)
	{
		printf("没找到\n");
	}
	else
		printf("%s",tmp);

	system("pause");
	return 0;
}

模拟实现strrstr：

#include<stdio.h>
#include<stdlib.h>
#include<assert.h>
char* my_strstr(const char *dest, const char *src)
{
	const char *cp = dest;
	const char *p = src;
	const char *start = NULL;
	while(*cp)
	{
		start = cp;
		while(*cp && *p && *cp == *p)
		{
			cp++;
			p++;
		}
		if(*p == '\0')
		{
			return (char *)start;
		}
		cp = start+1;
		p = src;
	}
	return NULL;
}
char* my_strrstr(const char *dest, const char *src)
{
	char *p = NULL;
	assert(dest != NULL);
	assert(src != NULL);
	while (*dest)
	{
		if (my_strstr(dest, src))
		{
			p = my_strstr(dest, src);
			dest = p + 1;
		}
		else
		{
			return p;
		}
	}
	return p;
}
int main()
{
	char arr[] = "abcdefgbcd";
	char arr1[] = "bcd";
	char *cp = my_strstr(arr, arr1);
	char *p = my_strrstr(arr, arr1);
	if (cp == NULL)
	{
		printf("没找到\n");
	}
	else
		printf("%s\n", cp);
	if (p == NULL)
	{
		printf("没找到\n");
	}
	else
		printf("%s\n", p);
	system("pause");
	return 0;
}

模拟实现strchr：

#define _CRT_SECURE_NO_WARNINGS 1

#include<stdio.h>
#include<assert.h>
char *my_strchr(char *str, int key)
{
	assert(str != NULL);
	while (*str != '\0')
	{
		if (*str == key)
		{
			return str;
		}
		str++;
	}
	return NULL;
}
int main()
{
	char arr[] = "hello world!";
	int n = 0;
	printf("请输入你要查找的字符：");
	scanf("%c", &n);
	char* ret = my_strchr(arr, n);
	printf("%s\n", ret);
	return 0;
}

模拟实现strrchr：

#define _CRT_SECURE_NO_WARNINGS 1

#include<stdio.h>
#include<assert.h>
char *my_strrchr(char *str, int key)
{
	assert(str != NULL);
	char * ret = 0;
	while (*str != '\0')
	{
		if (*str == key)
		{
			ret = str;
		}
		str++;
	}
	if (ret != 0)
	{
		return ret;
	}
	else
		return NULL;
}
int main()
{
	char arr[] = "hello world";
	int n = 0;
	printf("请输入你要查找的字符：");
	scanf("%c", &n);
	char *ret = my_strrchr(arr, n);
	printf("%s\n", ret);
	return 0;
}