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Copy pathstrops.c
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139 lines (127 loc) · 3.05 KB
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//常用字符串函数实现
//Wed Aug 13 01:06:50 PDT 2014
#include <stdio.h>
#include <string.h>
#include <assert.h>
//实现strcpy方法一
char* mystrcpy(char* strDes, const char* strSrc)
{
if (strDes == strSrc)
return strDes;
assert(strDes != NULL && strSrc != NULL);
char* des = strDes;
while ((*strDes++ = *strSrc++) != '\0');
return strDes;
}
//实现strncpy方法一
char* mystrncpy(char *dst, const char *src, size_t size)
{
assert((src != NULL) && (dst != NULL));
char *add = dst;
//int i = 0; // 控制复制的个数
while ((*dst++ = *src++)!='\0' && size-- > 0)
{
/*do nothing*/
}
if (*(--dst) != '\0') //注意字符串以'\0'结尾
{
*dst = '\0';
}
return add;
}
//char* mystrncpy(char* dest, const char* src, int len)
//{
// assert(dest!=NULL && src!=NULL);
//
// char* temp=dest;
// //int i=0;
//
// //while(i++ < len && (*temp++ = *src++)!='\0');
// while(len-->0 && (*temp++ = *src++)!='\0'); //要么长度限制，此时设*temp = '\0',
//
// if (*temp != '\0')
// *temp='\0';
//
// return dest;
//}
//char* strncpy(char* strDes, const char* strSrc, size_t n)
//{
// assert(strDes != NULL && strSrc != NULL && n > 0);
// if (strDes == strSrc)
// return strDes;
// char *des = strDes;
// for (; strSrc && n > 0; ++des, ++strSrc, --n)
// *des = *strSrc;
// for (; n > 0; --n)
// *des = '\0';
// return strDes;
//}
//C标准库实现strcpy
//没有处理空指针，原字符串与目标字符串相同
char* mystrcpy2(char *s1, const char *s2)
{
char *s;
for (s = s1; (*s++ = *s2++) != '\0'; )
;
return s1;
}
//C标准库实现strncpy
//没有处理空指针
char* mystrncpy2(char *s1, const char *s2, size_t n)
{
char* s;
for (s = s1; 0 < n && *s2 != '\0'; --n)
*s++ = *s2++;
for (; 0 < n; --n)
*s++ = '\0';
return s1;
}
//没有考虑到内存重叠的情况
void* mymemcpy(void *des, void *src, size_t n)
{
assert(des != NULL && src != NULL && n > 0);
char *pdes = (char*) des;
const char *psrc = (const char*) src;
while (n-- > 0)
{
*pdes++ = *psrc++;
}
return des;
}
//考虑内存重叠的情况，类似memmove
void* mymemcpy2(void *des, void *src, size_t n)
{
assert(des != NULL && src != NULL && n > 0);
if ( src < des && (char*)src + n > (char*)des)
{
char *pdes = (char*)des + n - 1;
const char *psrc = (const char*)src + n - 1;
while (n-- > 0)
{
*pdes-- = *psrc--;
}
}
else
{
char *pdes = (char*)des;
const char *psrc = (const char*)src;
while (n-- > 0)
{
*pdes++ = *psrc++;
}
}
return des;
}
int main()
{
char str1[10];
char str2[10];
//mystrcpy(str1, "hello");
mystrncpy(str1, "hello", 3);
//mystrcpy2(str2, "World");
//mystrncpy2(str2, "World", 2000000);
strncpy(str2, "hello", 3);
printf("str1=%s\n", str1);
printf("str2=%s\n", str2);
return 0;
}