常见的字符串处理函数实现

char* strcpy(char* strDest,const char* strSrc)
{
assert(strDest!=NULL && strSrc!=NULL);
char* strTmp = strDest;
while(*strSrc!='\0')
{
*strDest++ = *strSrc++;
}
strDest = '\0';
return strTmp;
}

void * memcpy(void* strDest,void* strSrc,size_t size)
{
assert(strDest!=NULL && strSrc != NULL);
void* strTmp = strDest;
//考虑内存重叠情况 类似memmove
if (strDest<=strSrc || (char*)strDest >= (char*)strSrc+size)
{
while(size--)
{
*(char*)strDest = *(char*)strSrc;
strDest = (char*)strDest + 1;
strSrc = (char*)strSrc + 1;
}
}
else
{
strDest = (char*)strDest+size-1;
strSrc = (char*)strSrc +size-1;
while(size--)
{
*(char*)strDest = *(char*)strSrc;
strDest = (char*)strDest-1;
strSrc = (char*)strSrc-1;
}
}
return strTmp;
}

int strlen(const char*strSrc)
{
assert(strSrc!= NULL);
int len = 0;
while((*strSrc++)  != '\0')
++len;
return len;
}

char* strcat(char* strDest,const char* strSrc)
{
assert((strDest != NULL) && (strSrc != NULL));
char* strTmp = strDest;
while(*strDest != '\0')
++strDest;
while(*strDest++ = *strSrc++)
;
*strDest++ = '\0';
return strDest;
}

int myAtoi(char* strSrc)
{
int iValue = 0;
int flag=0;
while (*strSrc == ' ')
{
strSrc++;
}
if(*strSrc == '-')
{
flag = -1;
}
else if(*strSrc == '+')
{
flag = 1;
}
else if(*strSrc > '9' || *strSrc < '0')
{
return 0;
}
while(*strSrc>='0' && *strSrc <= '9' && *strSrc )
{
iValue = iValue*10 + *strSrc -'\0';
strSrc++;
}
if(flag == 0)
iValue = iValue*(-1);
return  iValue;
}

bool isPalindrome(char* input)
{
if(input == NULL)
return false;
char* strBegin = input;
char* strEnd = input+strlen(input)-1;
while (strBegin < strEnd)
{
if(*strBegin++ != *strEnd--)
return false;
}
return true;
}

把一个char组成的字符串循环右移n个
void loopMove(char* pStr,int steps)
{
int nLen = strlen(pStr);
if(nLen <= 0 || steps == 0)
return;
int nStep = steps % nLen;
if(nStep == 0)
return;
char strTmp[128];
memcpy(strTmp,pStr+nLen-nStep,nStep);
memcpy(strTmp+nStep,pStr,nLen-nStep);
memcpy(pStr,strTmp,nLen);
}