1.实现strcpy
#include<stdio.h>
#include<assert.h>
char* m_strcpy(char* dest, const char* src)
{
char *ret = dest;
assert(dest != NULL );//断言
assert(src != NULL);//断言
逐位复制
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.实现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’,从此处开始复制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.实现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的首字符,然后进行比较,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.实现strchr
#include<stdio.h>
#include<assert.h>
char* m_strchr(char* dest, char a)
{
//在dest中逐个查找a,直到在dest中找到a或者找完dest(*dest==‘\0’)为止
while(*dest != '\0' && *dest != a)
{
++dest;
}
//如果查找结束后,dest=a 表示找到了,返回当前dest的地址,如果dest为\0,表示没找到,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.实现strcmp
#include<stdio.h>
#include<assert.h>
int m_strcmp(const char* str1, const char* str2)
{
assert(*str1);
assert(*str2);
//从第一个字符逐个判断大小,直到有字符串(一个或两个)结束
while(*str1 != '\0' && *str2 != '\0')
{
if(*str1 < *str2)
{
return -1;
}
else if(*str1 > *str2)
{
return 1;
}
else
{
++str1;
++str2;
}
}
//再次进行判断,哪一个字符串先结束,还是一起结束
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.实现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)
{
//想要复制,首先要强转类型,因为void是不可以复制的
*(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.实现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);
//保证dest不在src--src+n的范围里内
if(dest <= src || (char*)dest >=(char*)src + n)
{
//如果不在 正常拷贝
for(i = 0; i<n; ++i)
{
*(char*)dest = *(char*)src;
dest = (char*)dest+1;
src = (char*)src+1;
}
}
else
{
//如果在 反着拷贝
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;
}