send string from process to process using shared memory

Question

I'm new with shared memory , and i have tried these codes to send a string from process to another , and when the other process recives the string , it set the first character on the shared memory equal to 'a' character . but when i want to run one of them , i get segmentation fault message :

     #include <stdlib.h>
        #include<stdio.h>
        #include <string.h>
        int main(int argc , char *argv[])
        {
            key_t key = 111 ;
            int id = shmget(key , 512 , 1 | 0666);
            char *s  = shmat(id  , 0 , 0) ; 
            strcpy(s,argv[1]) ; 
            while(*s == 'a') sleep(1) ;
            return 0 ;
        }
   // and this is the code for reciever >     
        #include <stdlib.h>
        #include<stdio.h>
        int main(int argc , char *argv[])
        {
            key_t key = 111 ;
            int id = shmget(key , 512 , 1 | 0666);
            char* shm = shmat(id , 0 , 0 ) ;
            char *s = shm ; 
            for(s =  shm; *s != NULL ; s++ )
                putchar(*s) ;
            *s = 'a' ;
            return 0 ;
        }

Answer 1

I solve it , i include the following libraries --> and , and change the last input of shmget funciton to IPC_CREAT | 0666

Answer 2

It looks like in your for loop, you are incrementing your 's' variable, so you are not actually setting the first character of your string to 'a', but rather the null-terminator to 'a'.

Try changing

*s = 'a';

To

*shm = 'a';