This is svmsg/svmsg_create.c (Listing 46-1, page 938), an example from the book, The Linux Programming Interface.

The source code file is copyright 2022, Michael Kerrisk, and is licensed under the GNU General Public License, version 3.

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In the listing below, the names of Linux system calls and C library functions are hyperlinked to manual pages from the Linux man-pages project, and the names of functions implemented in the book are hyperlinked to the implementations of those functions.


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Function list (Bold in this list means a function is not static)

/* svmsg_create.c

   Experiment with the use of msgget() to create a System V message queue.
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#include <sys/stat.h>
#include "tlpi_hdr.h"
static void             /* Print usage info, then exit */
usageError(const char *progName, const char *msg)
    if (msg != NULL)
        fprintf(stderr, "%s", msg);
    fprintf(stderr, "Usage: %s [-cx] {-f pathname | -k key | -p} "
                            "[octal-perms]\n", progName);
    fprintf(stderr, "    -c           Use IPC_CREAT flag\n");
    fprintf(stderr, "    -x           Use IPC_EXCL flag\n");
    fprintf(stderr, "    -f pathname  Generate key using ftok()\n");
    fprintf(stderr, "    -k key       Use 'key' as key\n");
    fprintf(stderr, "    -p           Use IPC_PRIVATE key\n");
main(int argc, char *argv[])
    int numKeyFlags;            /* Counts -f, -k, and -p options */
    int flags, msqid, opt;
    unsigned int perms;
    long lkey;
    key_t key;

    /* Parse command-line options and arguments */

    numKeyFlags = 0;
    flags = 0;

    while ((opt = getopt(argc, argv, "cf:k:px")) != -1) {
        switch (opt) {
        case 'c':
            flags |= IPC_CREAT;

        case 'f':               /* -f pathname */
            key = ftok(optarg, 1);
            if (key == -1)

        case 'k':               /* -k key (octal, decimal or hexadecimal) */
            if (sscanf(optarg, "%li", &lkey) != 1)
                cmdLineErr("-k option requires a numeric argument\n");
            key = lkey;

        case 'p':
            key = IPC_PRIVATE;

        case 'x':
            flags |= IPC_EXCL;

            usageError(argv[0], "Bad option\n");

    if (numKeyFlags != 1)
        usageError(argv[0], "Exactly one of the options -f, -k, "
                            "or -p must be supplied\n");

    perms = (optind == argc) ? (S_IRUSR | S_IWUSR) :
                getInt(argv[optind], GN_BASE_8, "octal-perms");

    msqid = msgget(key, flags | perms);
    if (msqid == -1)

    printf("%d\n", msqid);


Download svmsg/svmsg_create.c

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