svmsg/svmsg_chqbytes.c

This is svmsg/svmsg_chqbytes.c (Listing 46-5, page 949), an example from the book, The Linux Programming Interface.

This page shows the "distribution" or "book" version of the file (why are there two versions?), or the differences between the two versions. You can switch between the views using the tabs below.

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.

Cover of The Linux Programming Interface

+/* svmsg_chqbytes.c
+
+   Usage: svmsg_chqbytes msqid max-bytes
+
+   Change the 'msg_qbytes' setting of the System V message queue identified
+   by 'msqid'.
+*/
 #include <sys/types.h>
 #include <sys/msg.h>
 #include "tlpi_hdr.h"
 
 int
 main(int argc, char *argv[])
 {
     struct msqid_ds ds;
     int msqid;
 
     if (argc != 3 || strcmp(argv[1], "--help") == 0)
         usageErr("%s msqid max-bytes\n", argv[0]);
 
     /* Retrieve copy of associated data structure from kernel */
 
     msqid = getInt(argv[1], 0, "msqid");
     if (msgctl(msqid, IPC_STAT, &ds) == -1)
         errExit("msgctl");
 
     ds.msg_qbytes = getInt(argv[2], 0, "max-bytes");
 
     /* Update associated data structure in kernel */
 
     if (msgctl(msqid, IPC_SET, &ds) == -1)
         errExit("msgctl");
 
     exit(EXIT_SUCCESS);
 }

Note that, in most cases, the programs rendered in these web pages are not free standing: you'll typically also need a few other source files (mostly in the lib/ subdirectory) as well. Generally, it's easier to just download the entire source tarball and build the programs with make(1). By hovering your mouse over the various hyperlinked include files and function calls above, you can see which other source files this file depends on.