I am reading data through a socket connected to a proxy, which in turn connects to a website of a choice, based on the IP and port I've assigned. After the successful connection, I am supposed to start sending headers to the server I've successfully connected to:

    ...
    char *request_header = "HEAD / HTTP/1.0\r\n";

    int response_size = 512;
    char *response_header = malloc(response_size * sizeof(char));

    write(proxy_fd, request_header, strlen(request_header));
    read(proxy_fd, response_header, response_size);

    printf("Response header:\n%s\n", response_header);
    free(response_header);
    ...

Now, creating a statically-allocated string array is problematic, because the response header can have any size. Is there a way to dynamically allocate the string response_header?

Inside <arpa/inet.h>, there are two functions to convert host byte order to network byte order. Why are there two options? I understand that htons() is used for port address related to IPv4 and IPv6, but what use does htonl() serve?

When I try running GNU indent on this particular code snippet:

#include    <stdio.h>
#include <stdlib.h>

Nothing happens? Why isn't indent dealing with the irregular space between #include and <stdio.h>?

In the book authored by K.N.King, there's this example:

/* Allows the user to view regions of computer memory */

#include <stdio.h>
#include <ctype.h>

typedef unsigned char BYTE;

int main(void)
{
	unsigned int addr;
	int i, n;
	BYTE *ptr;
	
	printf("Address of main function: %x\n", (unsigned int) main);
	printf("Address of addr variable: %x\n", (unsigned int) &addr);
	printf("\nEnter a (hex) address: ");
	scanf("%x", &addr);
	printf("Enter number of bytes to view: ");
	scanf("%d", &n);
	
	printf("\n");
	printf(" Address               Bytes             Characters\n");
	printf(" ------- ------------------------------- ----------\n");
	
	ptr = (BYTE *) addr;
	for (; n > 0; n -= 10) {
		printf("%8X  ", (unsigned int) ptr);
		for (i = 0; i < 10 && i < n; i++)
			printf("%.2X ", *(ptr + i));
		for (; i < 10; i++)
			printf("   ");
		printf(" ");
		for (i = 0; i < 10 && i < n; i++) {
			BYTE ch = *(ptr + i);
			if (!isprint(ch))
				ch = '.';
			printf("%c", ch);
		}
		printf("\n");
		ptr += 10;
	}
	
	return 0;
}

For some reason, when I try to enter addr variable address as the parameter, it has a segmentation fault error. However, in the book's example and the screenshot from this site in Hangul, there's no such error?

When I try using gdb to check the issue, here's what I get:

$ gdb ./a.out  --silent
Reading symbols from ./a.out...
(gdb) run
Starting program: /home/<username>/Desktop/c-programming-a-modern-approach/low-level-programming/a.out 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/gnu/store/zvlp3n8iwa1svxmwv4q22pv1pb1c9pjq-glibc-2.39/lib/libthread_db.so.1".
Address of main function: 401166
Address of addr variable: ffffd678

Enter a (hex) address: ffffd678
Enter number of bytes to view: 64

 Address               Bytes             Characters
 ------- ------------------------------- ----------

Program received signal SIGSEGV, Segmentation fault.
0x000000000040123a in main () at viewmemory.c:31
warning: Source file is more recent than executable.
31	        printf ("%.2X ", *(ptr + i));
(gdb)

What is going on? By the way, I am using Guix, if that matters in any way. Here's the output for ldd:

$ ldd ./a.out 
	linux-vdso.so.1 (0x00007ffecdda9000)
	libgcc_s.so.1 => /gnu/store/w0i4fd8ivrpwz91a0wjwz5l0b2ralj16-gcc-11.4.0-lib/lib/libgcc_s.so.1 (0x00007fcd2627a000)
	libc.so.6 => /gnu/store/zvlp3n8iwa1svxmwv4q22pv1pb1c9pjq-glibc-2.39/lib/libc.so.6 (0x00007fcd2609c000)

Second representation requires at least 6 bits to represent numbers between 0 to 59. But 5 bits are not just enough - 2^5^ = 32, which can only represent from 0 up to 31 seconds.

According to K.N. King:

You may be wondering how it 's possible to store the seconds - a number between 0 and 59 in a field with only 5 bits. Well. DOS cheats: it divides the number of seconds by 2, so the seconds member is actually between 0 and 29.

That really makes no sense?

It looks very similar to scope, so I really don't understand the difference. What makes storage classes different from each other? How is auto not the same as static, extern or register?

im new to system programming, idk if thats the issuse. but according gcc, it can not find dbus/dbus-arch-deps.h and thats all i know. any idea about this issue?

 program
[I] tomri@artix ~ [1]> cat main.c
#include <dbus-1.0/dbus/dbus.h>

int main(void) { return 0; }

# error
[I] tomri@artix ~> gcc main.c
In file included from main.c:1:
/usr/include/dbus-1.0/dbus/dbus.h:29:10: fatal error: dbus/dbus-arch-deps.h: No such file or directory
   29 | #include <dbus/dbus-arch-deps.h>
      |          ^~~~~~~~~~~~~~~~~~~~~~~
compilation terminated.

[I] tomri@artix ~> ls -la /usr/include/dbus-1.0/dbus/
total 216
drwxr-xr-x 2 root root  4096 Jul  2 20:26 ./
drwxr-xr-x 3 root root  4096 Jun 15 21:36 ../
-rw-r--r-- 1 root root  2809 Jan 14 06:17 dbus-address.h
-rw-r--r-- 1 root root  3470 Jan 14 06:17 dbus-bus.h
-rw-r--r-- 1 root root 27018 Jan 14 06:17 dbus-connection.h
-rw-r--r-- 1 root root  2909 Jan 14 06:17 dbus-errors.h
-rw-r--r-- 1 root root 22076 Jun  8  2023 dbus-glib-bindings.h
-rw-r--r-- 1 root root  2575 Jun  8  2023 dbus-glib-lowlevel.h
-rw-r--r-- 1 root root 14766 Jun  8  2023 dbus-glib.h
-rw-r--r-- 1 root root  8969 Jun  8  2023 dbus-gtype-specialized.h
-rw-r--r-- 1 root root  1464 Jun  8  2023 dbus-gvalue-parse-variant.h
-rw-r--r-- 1 root root  7246 Jan 14 06:17 dbus-macros.h
-rw-r--r-- 1 root root  1961 Jan 14 06:17 dbus-memory.h
-rw-r--r-- 1 root root 15259 Jan 14 06:17 dbus-message.h
-rw-r--r-- 1 root root  1810 Jan 14 06:17 dbus-misc.h
-rw-r--r-- 1 root root  3809 Jan 14 06:17 dbus-pending-call.h
-rw-r--r-- 1 root root 23956 Jan 14 06:17 dbus-protocol.h
-rw-r--r-- 1 root root  5412 Jan 14 06:17 dbus-server.h
-rw-r--r-- 1 root root  5392 Jan 14 06:17 dbus-shared.h
-rw-r--r-- 1 root root  3047 Jan 14 06:17 dbus-signature.h
-rw-r--r-- 1 root root  2359 Jan 14 06:17 dbus-syntax.h
-rw-r--r-- 1 root root  8505 Jan 14 06:17 dbus-threads.h
-rw-r--r-- 1 root root  4143 Jan 14 06:17 dbus-types.h
-rw-r--r-- 1 root root  3961 Jan 14 06:17 dbus.h
[I] tomri@artix ~> 

# my system
[I] tomri@artix ~> uname --all
Linux artix 6.9.7-artix1-1 #1 SMP PREEMPT_DYNAMIC Fri, 28 Jun 2024 18:11:28 +0000 x86_64 GNU/Linux

Is there a library for C, providing thread safe (high performance), and structured logging? An example for rust is the Tracing crate for rust (from Tokio). It should support several outputs as well.

cross-posted from: https://lemmy.ml/post/2650558

Highlights:

• More work on C2X features.

• The strlcpy and strlcat functions have been added. They are derived from OpenBSD, and are expected to be added to a future POSIX version.

• Support for x86_64 running on Hurd has been added.

• CVE-2023-25139: When the printf family of functions is called with a format specifier that uses an (enable grouping) and a minimum width specifier, the resulting output could be larger than reasonably expected by a caller that computed a tight bound on the buffer size. The resulting larger than expected output could result in a buffer overflow in the printf family of functions.

Let's say I have two arrays that have related data:

const char *backend_short[] = { "oal", "pa", "sdl_m" };
const char *backend_long[] = { "openal", "portaudio", "sdl_mixer" };

Does C support a way to "assert" that these two arrays have the same size? And failing compilation if they are different? I want a safeguard in case I'm drunk one day and forget to keep these synchronized.

Thanks in advance.

EDIT: I found a solution. Here are some enlightening resources on the matter:

• https://www.pixelbeat.org/programming/gcc/static_assert.html
• https://www.embedded.com/catching-errors-early-with-compile-time-assertions/

If one has POSIX extensions available, then it seems that defining _POSIX_C_SOURCE and just using getline or detdelim is the way to go. However, for source that is just C, here is a solution I've found from various sources, mainly here. I've also tried to make it more safe.

// Read line from stdin

#include <stdio.h>
#include <stdlib.h>

#define CHUNK_SIZE 16 // Allocate memory in chunks of this size

// Safe self-realloc
void *xrealloc(void *ptr, size_t size)
{
    void *tmp = realloc(ptr, size);
    if (!tmp) free(ptr);
    return tmp;
}

// Dynamically allocate memory for char pointer from stdin
char *readline(void)
{
    size_t len = 0, chunk = CHUNK_SIZE;
    char *str = (char *)malloc(CHUNK_SIZE);
    if (!str) return NULL;
    int ch;
    while((ch = getchar()) != EOF && ch != '\n' && ch != '\r') {
        str[len++] = ch;
        if (len == chunk) {
            str = (char *)xrealloc(str, chunk+=CHUNK_SIZE);
            if (!str) return NULL;
        }
    }
    str[len++] = '\0'; // Ensure str is null-terminated
    return (char *)xrealloc(str, len);
}

int main(void)
{
    setbuf(stdout, NULL); // Ensure environment doesn't buffer stdout
    printf("Enter name: ");
    char *userName = readline();
    if (!userName) return 1;
    printf("Hello, %s!\n", userName);
    free(userName);
    return 0;
}

The idea is that we allocate in chunks of 16, or whichever size. xrealloc is handy when reallocating a block of memory to itself.

int *ptr = malloc(sizeof(int) * 4);
ptr = (int *)realloc(ptr, sizeof(int) * 8);

If realloc fails, ptr gets assigned NULL, and we lose the address that we need to free, causing a memory leak. So, xrealloc allows for safe self re-allocation.

I am not the author of dwl. Since dwl is based on wlroots (just like the popular Sway) it already supports making screenshots using grim and screencasts using wf-recorder.

You can try out dwl from within your current WM. The default modkey is Alt. If you want to use the Super key, change #define MODKEY WLR_MODIFIER_ALT in config.h to #define MODKEY WLR_MODIFIER_LOGO and recompile. The default terminal emulator is kitty but you can change termcmd to alacritty if you want.

Currently, only native Wayland applications run on it. You can enable experimental Wayland support for Firefox with MOZ_ENABLE_WAYLAND=1, see Running programs natively under Wayland in Sway Wiki.

Do not hover over the edges of windows – this will crash dwl.

Hello fellow lemmys (or however do we call us?),

as the title suggests, I am looking for someone who wants to learn the C programming language. I have a decent knowledge of computer science and of a couple of programming languages (C#, Java, Python). Currently, I am studying computer science in central/western Europe. In my opinion, studying together keeps each other motivated and is more efficient. In long terms, I hope, that we can contribute to open-source projects together and improve our code quality by reviewing each others code.

If any of you has some interest in being my programming buddy, please message me or reply to this post. Preferably from a similar time zone (mine is UTC+01:00).

Hoping for some replies

Regards