字符串处理函数的实现

喜欢ヅ旅行 2022-07-14 00:09 207阅读 0赞

**1、strcpy函数的实现**

#define _CRT_SECURE_NO_WARNINGS 1
    #include<stdio.h>
    #include<stdlib.h>
    #include<assert.h>
    #include<string.h>
    char *My_strcpy(char *dst, const char *str)
    { 	
    	assert(dst);
    	assert(str);
    	while (*dst++ = *str++);
    	return dst;
    }
    int main()
    {
    	char *src = "ABCDE";
    	char dest[]="12345";
    	My_strcpy(dest, src);
    	printf("%s", dest);
    	system("pause");
    	return 0;
    
    }

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**2、strncpy函数的实现**

#define _CRT_SECURE_NO_WARNINGS 1
    #include<stdio.h>
    #include<stdlib.h>
    #include<assert.h>
    #include<string.h>
    char *My_strncpy(char *dst, const char *str, size_t count)
    { 
    	assert(dst);
    	assert(str);
    	assert(count > 0);
    	while (count--)
    	{
    		*dst++ = *str++;
    	}
    	*dst = '\0';
    	return dst;
    }
    int main()
    {
    	char *src = "ABCDEGFYTRHUUUUUU";
    	char dest[64];
    	int len = strlen(src);
    	int num = 0;
    	scanf("%d", &num);
    	if (num < len)
    	{
    		My_strncpy(dest, src, num);
    		printf("%s", dest);
    	}
    	else
    	{
    		printf("输入错误");
    	}
    	system("pause");
    	return 0;
    }

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**3、strcat函数的实现**

#define _CRT_SECURE_NO_WARNINGS 1
    #include<stdio.h>
    #include<stdlib.h>
    #include<assert.h>
    #include<string.h>
    char *My_strcat(char *dst, const char *str)
    {
    	assert(dst);
    	assert(str);
    	int len1 = strlen(dst);
    	int len2 = strlen(str);
    	char *Buff = NULL;
    	char *end = NULL;
    	Buff = (char *)malloc(len1 + len2+1);
    	strcpy(Buff, dst);
    	end = Buff + len1;
    	strcpy(end, str);
    	printf("%s", Buff);
    	return dst;
    }
    
    int main()
    {
    	char *src = "ABCDEFGGGGGGG";
    	char dest[] = "12345";
    	My_strcat(dest, src);
    	system("pause");
    	return 0;
    
    }

![Center 2][]

**4、strncat函数的实现**

#define _CRT_SECURE_NO_WARNINGS 1
    #include<stdio.h>
    #include<stdlib.h>
    #include<assert.h>
    #include<string.h>
    char *My_strncat(char *dst, const char *str, size_t count)
    {
    	int len1 = strlen(dst);
    	int len2 = strlen(str);
    	char *Buff = NULL;
    	char *end = NULL;
    	Buff = (char *)malloc(len1 + len2+1);
    	strcpy(Buff, dst);
    	end = Buff + len1;
    	while (count--)
    	{
    		*end++ = *str++;
    	}
    	*end = '\0';
    	printf("%s", Buff);
    }
    int main()
    {
    	char *src = "ABCDEFGHIGK";
    	char dst[] = "123456789";
    	int num = 0;
    	scanf("%d", &num);
    	My_strncat(dst, src, num);
    	system("pause");
    	return 0;
    
    }

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**5、strcmp函数的实现**

int My_strcmp(const char *str1, const char *str2)
    {
    	assert(str1);
    	assert(str2);
    	while (*str1 != '\0', *str2 != '\0')
    	{
    		if (*str1 == *str2)
    		{
    			str1++;
    			str2++;
    		}
    		if (*str1 > *str2)
    		{
    			return 1;
    		}
    		if (*str1 < *str2)
    		{
    			return -1;
    		}
    	}
    	if (*str1 == '\0'&&*str2 != '\0')
    	{
    		return -1;
    	}
    	if (*str2 == '\0'&&*str1 != '\0')
    	{
    		return -1;
    	}
    	return 0;
    }
    int main()
    {
    	char *str1 = "ABCDEFGH";
    	char *str2 = "ABCDEFGH";
    	if (My_strcmp(str1, str2) == 0)
    	{
    		printf("两个字符串相等");
    	}
    	if (My_strcmp(str1, str2) == 1)
    	{
    		printf("字符串1大于字符串2");
    	}
    	if (My_strcmp(str1, str2) ==-1)
    	{
    		printf("字符串1小于字符串2");
    	}
    	system("pause");
    	return 0;
    }

![Center 4][]

**6、strncmp函数的实现**

#define _CRT_SECURE_NO_WARNINGS 1
    #include<stdio.h>
    #include<stdlib.h>
    #include<assert.h>
    #include<string.h>
    int My_strncmp(const char *str1, const char *str2, size_t count)
    {
    	assert(str1);
    	assert(str2);
    	while (count--)
    	{
    		if (*str1 != '\0'&&*str2 != '\0')
    		{
    			if (*str1 > *str2)
    			{
    				return 1;
    			}
    			if (*str1 <*str2)
    			{
    				return -1;
    			}
    			if (*str1 == *str2)
    			{
    				str1++;
    				str2++;
    			}
    
    		}
    		if (*str1 == '\0'&&*str2 != '\0')
    		{
    			return -1;
    		}
    		if (*str2 == '\0'&&*str1 != '\0')
    		{
    			return -1;
    		}
    	}
    }
    
    
    int main()
    {
    	char *str1 = "ABCDEFGH";
    	char *str2 = "ABCDEWGH";
    	int num = 0;
    	scanf("%d", &num);
    	if (My_strncmp(str1, str2, num) == 0)
    	{
    		printf("两个字符串相等");
    	}
    	if (My_strncmp(str1, str2, num) == 1)
    	{
    		printf("字符串1大于字符串2");
    	}
    	if (My_strncmp(str1, str2, num) == -1)
    	{
    		printf("字符串1小于字符串2");
    	}
    	system("pause");
    	return 0;
    }

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**7、memcpy函数的实现：复制后会覆盖部分原有数据**

#define _CRT_SECURE_NO_WARNINGS 1
    #include<stdio.h>
    #include<stdlib.h>
    #include<assert.h>
    #include<string.h>
    void *memcpy(void *dst, const void *str, size_t count)
    {   
    	assert(dst);
    	assert(str);
    	void *ret = dst;
    	while (count--)
    	{
    		*(char*)dst = *(char*)str;
    		dst=(char*)dst+1;
    		str=(char*)str + 1;
    
    	}
    	return dst;
    }
    int main()
    {
    	char *src = "ABCDE";
    	char dest[] ="BBBBBBBBBB";
    	int num = 0;
    	scanf("%d", &num);
    	memcpy(dest, src, num);
    	printf("%s", dest);
    	system("pause");
    	return 0;
    }

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**8、memmove函数的实现**

#define _CRT_SECURE_NO_WARNINGS 1
    #include<stdio.h>
    #include<stdlib.h>
    #include<assert.h>
    #include<string.h>
    void *My_memmove(void *dst, const void *str, size_t count)
    {
    	assert(str);
    	void *ret = dst;
    	if (dst <= str || (char*)dst >= ((char*)str + count))
    	{
    		while (count--)
    		{
    			assert(dst);
    			*(char*)dst = *(char *)str;
    			dst = (char*)dst + 1;
    			str = (char *)str + 1;
    
    		}
    
    	}
    	else
    	{
    		(char*)dst = (char*)dst + count - 1;
    		(char *)str = (char *)str + count - 1;
    		while (count--)
    		{
    			*(char*)dst = *(char *)str;
    			dst = (char*)dst - 1;
    			str = (char *)str - 1;
    
    		}
    
    	}
    	return ret;
    }
    int main()
    {
    	char *src = "AABCDE";
    	char dst[] = "AAAAABBBB";
    	My_memmove(dst, src, strlen(src) + 1);
    	printf("%s", src);
    	system("pause");
    	return 0;
    }

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