2018-2-7 test19

最新推荐文章于 2022-10-04 07:30:00 发布

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C语言

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本文提供了一系列C语言中常用字符串操作函数的手动实现版本，包括strcpy、strcat、strstr、strchr、strcmp及内存操作函数memcpy和memmove。通过这些代码示例，读者可以更好地理解这些函数的工作原理和实现细节。

模拟strcpy

#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
#include<windows.h>
#include<assert.h>

char* my_strcpy(char* x, char* y)
{
	assert(x);
	assert(y);
	char* p2 = x;
	while (*y != '\0')
	{
		*x++ = *y++;
	}
	*x = *y;
	return p2;
}

int main()
{
	char p[10] = { 0 };
	char *p1 = "hello1234";
	
	char *n = my_strcpy(p, p1);

	system("pause");
	return 0;

}

模拟strcat

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

char* my_strcat(char* x, char* y)
{
    assert(x);
    assert(y);
	char* p2 = x;
	while (*x != '\0')
	{
		x++;
	}
	while (*y != '\0')
	{
		*x++ = *y++;
	}
	*x = *y;
	return p2;
}
int main()
{
	char p[64] = "hello";
	char* p1 = "world";
	my_strcat(p, p1);
	system("pause");
	return 0;
}

模拟strstr

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

char* my_strstr(const char* x, const char* y)
{
	assert(x);
	assert(y);
	char* x1 = NULL;
	char* y1 = NULL;
	char* p = NULL;
	while (*x !='\0')
	{
		x1 = x;
		y1 = y;
		while ((*x1 != '\0') && (*y1 != '\0') && (*x1 == *y1))
		{
			x1++;
			y1++;
		}
		if (*y1 == '\0')
		{
			return x;
		}
		x++;
	}
	return NULL;
}
int main()
{
	const char* p = "abcdabcdehij";
	const char* p1 = "abcde";
	const char* p2 = my_strstr(p, p1);
	printf("%s", p2);
	system("pause");
	return 0;
}

模拟strchr

#include<stdio.h>
#include<windows.h>
#include<assert.h>
char *my_strchr(char *x, char y)
{
	assert(x);
	while (*x != '\0')
	{
		if (*x == y)
		{
			
			return x;
		}
		x++;
	}
	return NULL;
	
}
int main()
{
	char *p = "helloworld";
	char ch = 'd';
	char *p1 = my_strchr(p, ch);
	system("pause");
	return 0;
}

模拟strcmp

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

int my_strcmp(char* x, char* y)
{
	assert(x);
	assert(y);
	int ret = 0;
	while (*x != '\0'&&*y != '\0')
	{
		if (*x == *y)
		{
			x++;
			y++;
		}

		else if (*x > *y)
		{
			ret = 1;
			
			
		}
		else
			ret = -1;
		
	}
	if ((*x == '\0') && (*y == '\0'))
	{
		ret = 0;
	}
	else if (*x == '\0')
	{
		ret = -1;
	}
	else
	{
		ret = 1;
	}
	
	return ret;

}
int main()
{
		char* p = "hello";
		char* p1 = "helloo";
		printf("%d", my_strcmp(p, p1));
		system("pause");
		return 0;
}

模拟memcpy

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

void *my_memcpy(void *x, const void *y, int size )

{
    assert(x);
    assert(y);
	char *x1 = (char *)x;
	const char* y1 = (const char*)y;
	while (size--)
	{
		*x1++ = *y1++;
	}
	return x;
}
int main()
{
	char a[10] = { 0 };
	const char b[] = { 1,2,5,8,3,4,6,8,7 };
	int size = sizeof(b) / sizeof(b[0]);
	my_memcpy(a, b,size);

		system("pause");
		return 0;
}

模拟memmove

#include<stdio.h>
#include<windows.h>
#include<assert.h>
#include<string.h>
void *my_memmove(void *dst, const void *src, int size)
{
	void *ret = dst;
	if (((char*)src<(char*)dst) && (char*)src+size>(char *)dst)
	{
		src = (char*)src + size - 1;
		dst = (char*)src + size - 1;
		while (size--)
		{
			*(char*)dst = *(char*)src;
			dst = (char*)dst - 1;
			src = (char*)src - 1;
		}
	}
	else
	{
		while (size--)
		{
			*(char*)dst = *(char*)src;
			dst = (char*)dst + 1;
			src = (char*)src + 1;
		}
		return ret;
	}
}
int main()
{
	const char buf[32] = "abcd1234";
	char buf1[32] = { 0 };
	int size = strlen(buf);
	my_memmove(buf1, buf, strlen(buf));
	system("pause");
	return 0;
}