1.實現strcpy 

#include<stdio.h>
#include<assert.h>
char* m_strcpy(char* dest, const char* src)
{
	char *ret = dest;
	assert(dest != NULL );//斷言
	assert(src != NULL);//斷言
	逐位複製
 	while(*dest++ = *src++)
	{	
	;
	}
return ret;
}


int main()
{
	char arr1[1024] = {0};
	char *arr2 = "12345";
	
 m_strcpy(arr1,arr2);
printf("%s ", arr1);
system("pause");
return 0;
}
 

2.實現strcat 

#include<stdio.h>
#include<assert.h>
char* m_strcat(char* dest,const char* src)
{
	char* ret = dest;
	assert(*dest);
	assert(*src);
	//找到dest的‘\0’，從此處開始複製src
	while(*dest++)
	{
	;
	}
	
	while(*dest++ = *src++); 
return ret;
}


int main()
{
	char *arr1 = "abbbb";
	char *arr2 = "12345";
 m_strcat(arr1,arr2);
printf("%s ", arr1);
system("pause");
return 0;
}

 

3.實現strstr 

#include<stdio.h>
#include<assert.h>
char* m_strstr(const char* dest,const char* src)
{
	//在dest中找src
	// 在dest中找到src的首字元，然後進行比較，直到src到“\0”
const char* str = dest;
for(; *str != '\0'; ++str)
{
while(*str != '\0' && *src != '\0')
{
  if(*str == *src)
  {
  ++str;
  ++src;
  }
  else
  {
  break;
  }
}
if(*src == '\0')
{
return str;
}
return NULL;
}



 int main()
{
	char *arr1 = "abbbb";
	char *arr2 = "bb";
char* p = m_strstr(arr1,arr2);
printf("%p %p ", arr1, p );
system("pause");
return 0;
}
 

4.實現strchr 

#include<stdio.h>
#include<assert.h>
char* m_strchr(char* dest, char a)
{
//在dest中逐個查詢a，直到在dest中找到a或者找完dest（*dest==‘\0’）為止
while(*dest != '\0' && *dest != a)
{
++dest;
}
//如果查詢結束後，dest=a 表示找到了，返回當前dest的地址，如果dest為\0，表示沒找到，返回空
return *dest == a ? dest : NULL;
}




int main()
{
	char *p = "asdf";
	char p2 = 's';
		char* n =  m_strchr(p , p2);
printf("%p %p", n, p);
system("pause");
		return 0;
}

5.實現strcmp 

#include<stdio.h>
#include<assert.h>
int m_strcmp(const char* str1, const char* str2)
{
assert(*str1);
assert(*str2);
//從第一個字元逐個判斷大小，直到有字串（一個或兩個）結束
while(*str1 != '\0' && *str2 != '\0')
{
  if(*str1 < *str2)
  {
  return -1;
  }
  else if(*str1 > *str2)
  {
  return 1;
  }
  else
  {
  ++str1;
  ++str2;
  }
}
//再次進行判斷，哪一個字串先結束，還是一起結束
if(*str1 < *str2)
  {
  return -1;
  }
  else if(*str1 > *str2)
  {
  return 1;
  }
  else
  {
  return 0;
  }
}

int main()
{
	char *p = "asdf";
	char *p2 = "asdf";
		int a =  m_strcmp(p , p2);
printf("%d ", a);
system("pause");
		return 0;
}

6.實現memcpy 

#include<stdio.h>
#include<assert.h>
void* m_memcpy(void* dest, void* src, size_t n)
{
void* ret = dest;
size_t i = 0;
for(i=0; i<n; ++i)
{
//想要複製，首先要強轉型別，因為void是不可以複製的
*(char*)dest = *(char*)src;
dest = (char*)dest+1;
src = (char*)src+1;
}
}



 int main()
{
	int i = 0;
	int arr1[] = {1, 2, 2, 3, 5};
	int arr2[10] = {0};
		m_memcpy(arr2 , arr1, sizeof(arr1));
		for(i=0; i<10; i++)
		{
		printf("%d\n", arr2[i]);
		}
system("pause");
		return 0;
}

7.實現memmove

#include<stdio.h>
#include<assert.h>
void* m_memmove(void* dest, const void* src, size_t n)
{
	void* ret = dest;
	size_t i = 0;
assert(dest != NULL);
assert(src != NULL);

//保證dest不在src--src+n的範圍裡內
if(dest <= src || (char*)dest >=(char*)src + n)
{
//如果不在 正常拷貝
	for(i = 0; i<n; ++i)
	{
	*(char*)dest = *(char*)src;
	dest = (char*)dest+1;
src = (char*)src+1;
	}
}
else
{
//如果在  反著拷貝
	dest = (char*)dest+n-1;
src = (char*)src+n-1;
for(i = 0; i<n; ++i)
	{
	*(char*)dest = *(char*)src;
	dest = (char*)dest-1;
src = (char*)src-1;
	}
}
return ret;
}

 int main()
{
	int i = 0;
	int arr1[10] = {1, 2, 2, 3, 5};
	
		m_memmove(arr1+1 , arr1, sizeof(arr1));
		for(i=0; i<10; i++)
		{
		printf("%d\n", arr1[i]);
		}
system("pause");
		return 0;
}