模拟实现strcpy、strcat、strstr、strcmp、memcpy、memmove、strchr

1. To achieve strcpy
2. implement strcat
3. achieved Strstr
4. implement the strchr
5. The implement strcmp
6. The implement the memcpy
7. The implement memmove

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
//strcpy:将str2的字符串给str1
void my_cpy(char * str1, const char * str2){
	int i;
	int ret = strlen(str2);
	for (i = 0; i < ret; ++i){
		str1[i] = str2[i];
	}
	puts(str1);
}
int main(){
	char str1[20] = "abcdefgh";
	char str2[20] = "12345";
	my_cpy(str1, str2);
	system("pause");
	return 0;
}

//strcat:将str2拼接到str1后面
void my_cat(char *str1,const char *str2){
	int i;
	int ret = strlen(str2);
	int a = strlen(str1);
	for (i = 0; i < ret; ++i){
		str1[i + a] = str2[i];
	}
	puts(str1);
}
int main(){
	char str1[20] = "abcdefgh";
	char str2[20] = "12345";
	my_cat(str1, str2);
	system("pause");
	return 0;
}

//strstr:查找str1里面是否有str2
int my_str(const char * str1, const char * str2){
	char *start1 = (char *)str1;
	char *start2 = (char *)str2;
	char *p = (char *)str1;
	assert(str1 != NULL);
	assert(str2 != NULL);
	while (*p){
		start1 = p;
		while (*start1 != '\0'&&*start2 != '\0'&&*start1 == *start2){
			start1++;
			start2++;
		}
		if (*start2 == '\0'){
			printf("%s\n",p);
		}
		start2 = (char *)str2;
		p++;
	}
	return 0;
}
int main(){
	char a[20] = "abbbcdef";
	char b[10] = "bbcde";
	printf("%s\n", my_str(a, b));
	system("pause");
	return 0;
}

//strchr:在字符串里面查找字符
char *my_strchr(const char *str1, char str2)
{
	char *m = NULL;
	while (*str1 != NULL)
	{
		if (*str1 == str2)
		{
			return (char *)str1;
		}
		*str1++;
	}
	return NULL;
}

int main()
{
	char *a = "abcderf";
	char b = 'e';
	char *c = NULL;
	c = my_strchr(a, b);
	printf("%s\n", c);
	system("pause");
	return 0;
}

//strcmp:比较两个字符串是不是相等
int my_strcmp(char const *s1, char const *s2)
{
	assert(s1 != NULL);
	assert(s2 != NULL);
	int ret = 0;
	while (!(ret = (*s1 - *s2)) && *s1 && *s2)//如果两者相等且不为'\0'
	{
		s1++;
		s2++;
	}
	if (ret < 0)
		ret = -1;
	else if (ret>0)
		ret = 1;
	return ret;
}
int main()
{
	char *s1 = "abcd";
	char*s2 = "abbb";
	printf("%d\n", my_strcmp(s1, s2));
	system("pause");
	return 0;
}

//memcpy:内存拷贝
void* my_memcpy(void* dest, void* src, size_t n)
{
	void* ret = dest;
	char* str1 = (char*)dest;
	char* str2 = (char*)src;
	assert(dest);
	assert(src);
	while (n--)
	{
		*str1++ = *str2++;
	}
	return ret;
}
//内存移动
void* my_memmove(void* dest, void* src, size_t n)
{
	void* ret = dest;
	char* str1 = (char*)dest;
	char* str2 = (char*)src;
	assert(dest);
	assert(src);
	if (str1 > str2)
	{
		while (n--)
		{
			*(str1 + n) = *(str2 + n);
		}
	}
	else
	{
		while (n--)
		{
			*str1++ = *str2++;
		}
	}
	return ret;
}
int main()
{
	int i = 0;
	int arr1[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
	int arr2[10] = { 0 };
	int arr3[10] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
	my_memcpy(arr2, arr1, sizeof(arr1));
	my_memmove(arr3 + 5, arr3 + 4, 3 * sizeof(int));
	for (i = 0; i < 10; i++)
	{
		printf("%d ", arr2[i]);
	}
	printf("\n");
	for (i = 0; i < 10; i++)
	{
		printf("%d ", arr3[i]);
	}
	system("pause");
	return 0;
}