为什么编译通过了，执行时出现应用程序错误该内存不能为writtet

#include<stdio.h>#include<string.h>
char *loopmove(char *pstr,int steps)
{
int n=strlen(pstr)-steps;
char tmp[50];
strcpy(tmp,pstr+n);
strcpy(tmp+steps,pstr);
*(tmp+strlen(pstr))='\0';
strcpy(pstr,tmp);
return(pstr);
}
int main()
{
char *a={"asdfghjkl"};
int b=3;
loopmove(a,b);
printf("%s",a);
}