How to read/write from/to shared memory

get_shm.cpp

#include <stdio.h>
#include <sys/ipc.h>
#include <sys/shm.h>

#define SHKEY 0x11213007	 

int main() {

	int shm_id = shmget( SHKEY , 32, 0666 );
	if ( shm_id != -1 ) {
		char *str = (char *) shmat( shm_id, NULL, 0 );
    		printf("shared mem = |%s|\n", str );
	} else {
		printf("unable to get shmid , key is 0x%x\n", SHKEY);
	}
	return 0;
}

put_shm.cpp

#include <stdio.h>
#include <sys/ipc.h>
#include <sys/shm.h>	 
#include <string.h>

#define SHKEY 0x11213007

int main( int argc , char *argv[] ) {

	char *str;
	int shm_id = shmget( SHKEY , 32, IPC_CREAT | 0666 );

	
	if ( shm_id != -1 ) {

		printf( " shm_id ok %d\n ", shm_id );
		str = (char *) shmat( shm_id, NULL, 0 );
		
		
		if ( str == (char *)-1 ) {
			printf("shmat error!\n");

		} else {
    			if ( argc > 1 ) {
				strcpy( str, argv[1] );
				printf( "%s has been put in shared mem\n", argv[1]);
			} else {
				printf("argv not supplied\n");
			}
		}
	} else {
		printf("unable to get shmid , key is 0x%x\n", SHKEY);
	}
	return 0;
}