Receiving error: assignment makes integer from pointer without a cast

Question

I have below program for shared memory access in C

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

#define SHMSZ 27

int main() {
    char c;
    int shmid;
    key_t key;
    char *shm, *s;

    key = 5678;
    /* Create the segment */
    if ((shmid = shmget(key, SHMSZ, IPC_CREAT | 0666)) < 0) {
        perror("shmget");
        exit(1);
    }

    /* Attach the segment */
    if ( (shm = shmat(shmid, NULL, 0)) == (char *) -1) {
        perror("shmat");
        exit(1);
    }

    /* Put things into memory for other processes to read*/
    s = shm;
    for (c = 'a'; c <= 'z'; c++) {
        *s++ = c;
    }
    *s = NULL; 

    /*Wait till other processes read and change the memory*/
    while (*shm != '*') {
           sleep(1);
    }

    exit(0);
}

In this program I am getting error for below line

   *s = NULL;

Error:

shm_server.c: In function ‘main’:
shm_server.c:36:8: warning: assignment makes integer from pointer without a cast [enabled by default]

Why am I receiving this error?

Note: I also have a other script as shm_client.c to read the memory while the server program shm_server.c waits till client program changes the first character to '*'

`*s = NULL; `->`*s = '\0';` – David Ranieri Feb 13 '15 at 11:12 — David Ranieri, Feb 13 '15 at 11:12

Vagish · Accepted Answer · 2015-02-13T11:57:15.257

1

If you want to write 'null' NOT 'NULL' at the end of data then do this:

*s = '\0';

OR

*s  = 0x00;

edited Feb 13 '15 at 11:57

answered Feb 13 '15 at 11:07

Vagish

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wont that NULL complete previous assignment done in while. I just want to add NULL as last element – Feb 13 '15 at 11:10
ok now it works. With the first one I was getting Segmentation fault. Since I have a other prog as shm_client.c to read the memory while the server script waits till shared memory is changed. – Feb 13 '15 at 11:17
Good that its working for you,If you do not have any more issues accept the answer. – Vagish Feb 13 '15 at 11:19
It is better explained here: http://stackoverflow.com/questions/1296843/what-is-the-difference-between-null-0-and-0 – Vagish Feb 13 '15 at 11:23
1

`NULL` is not an object. And (outside POSIX) not necessarily of pointer type. `#define NULL 0` is valid (and would have made the code compile). – mafso Feb 13 '15 at 11:49

Receiving error: assignment makes integer from pointer without a cast

1 Answers1