c++ - Why is Runtime Error popping up? -

can please me in this? why runtime error popping up? in advance:) not c++.

   #include <iostream>     #include<sys/types.h>     #include<sys/ipc.h>     #include<sys/shm.h>     #include<string.h>     #include<unistd.h>     #define key 123456     using namespace std;      int main()     {         int shmid=shmget(key, 128, 0666);         char* addr1=(char*)shmat(shmid, 0, 0);         strcpy(addr1, "hello");          int pid=fork();         if(pid!=0)         {             char* addr2=(char*)shmat(shmid,0,0);             std::cout<<"\n"<<addr1;             std::cout<<"\n"<<addr2;             sleep(2);             std::cout<<"\n"<<addr1;             std::cout<<"\n"<<addr2;             int rval=shmdt(addr2);             std::cout<<"\n"<<addr1;             std::cout<<"\n"<<addr2;         }         else         {             strcpy(addr1, "world");         }         return 0;     } 

can please me in this? why runtime error popping up? in advance:) not c++. can please me in this? why runtime error popping up? in advance:) not c++. sorry had make content larger.