algorithm/string/strops.c at master · viclab/algorithm · GitHub

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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;

}

algorithm/string/strops.c at master · viclab/algorithm · GitHub

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