對strcpy strcat strstr strchr strcmp memcpy memmove的自我編譯
阿新 • • 發佈:2018-12-09
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;
}