将一个字符串,左旋N个字符

#include "stdio.h"

size_t _strlen(char* str)
{
if (str==NULL || *str=='\0') return 0;

int count=0;
while (*str++)
{
count++;
}
return count;
}
void scroll_str(char* str,int step)
{
if (str==NULL || *str=='\0' || step<=0) return;
int len=_strlen(str);
int real_step=step%(len-1);

char c=*str;
char* p1=str;
char* p2=str+1;
for (int i=0;i<real_step;i++)
{

*p1=*p2;

p1++;
p2++;
}

*p1=c;

}
void main(void)
{
char a[]="Hello World!";
printf("%s\n",a);

scroll_str(a,10);

printf("%s\n",a);
}