Hello,

I'm looking at man-pages 6.7 installed in Ubuntu 26.04 and I notice the following in the memcpy page.

I guess that the restrict refers to the keyword restrict being integrated into LIBC, but what is this .n in dest and src? Does it mean that the dest and src pointers do not overlap on the first n bytes? Where is this syntax defined and what other interesting cases can be out there?

Thanks

SYNOPSIS

#include <string.h>

void *memcpy(void dest[restrict .n], const void src[restrict .n],

size_t n);

Hey everybody. I’m a beginner to C and I was writing some functions today to get used to doing things. I tried to write binary search and bubble sort. I tried to pass in an array as an argument to the functions, but the compiler gave me a bunch of warnings. I looked it up and I saw that passing in an array is the same as passing in its pointer. I haven’t touched pointers yet, but I have two questions:
1. If I dereferenced the pointer to an array, wouldn’t that return the same as indexing the first value?
2. If I wanted to pass in the entire array, could I do that by passing in the pointers of both the first and last elements and using pointer arithmetic to access the other elements? What’s the idiomatic way of doing this?

I just started learning C(2 days ago) and as a first project I decided to make some data structures, starting with dynamic arrays. I made a struct called List and some functions for. The function setList() sets the value of an index of the array, if the index is larger that the current size of the array, it resizes it. However, when i tried to use in a for loop, it didn't work despite it working elsewhere.

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


#define itirate(index, limit) for(int index = 0; index < limit; index++)


typedef struct 
{
    size_t size;
    int* arr;
} List;


List* newList (size_t size) 
{
    List *newone = malloc(sizeof(List));
    newone->arr = calloc(size, sizeof(int));
    newone->size = size;
    return newone;
}


void setList(List* list, int index, int value) 
{
    if (index >= list->size)
    {
        list->arr = realloc(list->arr, index + 1 * sizeof(int));
        list->size = index + 1;
    }


    list->arr[index] = value;
}


int main() 
{
    
    List *mok = newList(5);

    itirate(i, 5) setList(mok, i, i);
    itirate(i, 5) printf("%d\n", mok->arr[i]);

    //setList(mok, 13, 9); this works
    //printf("%d\n", mok->arr[13]);

    for(int i = 5; i < 10; i++) setList(mok, i, i); // this does not somehow
    for(int i = 5; i < 10; i++) printf("%d\n", mok->arr[i]);
    
    return 0;
}

#include <stddef.h>

static void *align_forward(void *address, size_t alignment) {
    size_t mask = alignment - 1U;
    size_t padding = (alignment - ((size_t)address & mask)) & mask;
    return (char *)address + padding;
}

I'm writing allocator just for fun and now I'm wondering if aligning pointer reliably on any platform without any implementation defined casts while conforming to C standard is even possible.

There is no aling_up function, uintptr_t is optional, and in the example we do cast from pointer to size_t that might cause truncation.

i know fork creates processes but how process ids are generated

I have a double* which has the following entries:

0.3333333333333334
0.6666666666666668
0.1249999999999999
1

Here, the last entry, 1, can be considered the right hand side of an inequality:

0.3333333333333334 x + 0.6666666666666668 y + 0.1249999999999999 z >= 1

These numbers come from a numerical linear algebra library over which I don't have any control. What is the easiest way to "convert" this to the following equivalent inequality (subject to a user provided tolerance of what counts as an epsilon so that epsilon within an integer is to be counted as an integer)?

8 x + 16 y + 3 z >= 24

Is there a package that does such conversion, if reasonably possible? I consider it unreasonably possible by multiplying everything in the original equation by a large enough power of 10. But I do not want that.

Background
Hi, I am a 15-year-old teen (just so what you'd know what to expect) who left school because our school system taught us to be parrots. I want to be a god-level developer, not a code monkey. I wrote a Sudoku GUI using win32api in C Language.
It is currently working and does what it is supposed to do, but because I am still learning, I know it is likely inefficient and could be written much better. 

Code : https://github.com/reewdgh/sudoku_gui.

Concerns:
Please guide me on:

Bugs or potential issues
Efficiency
How can I move to Tier 1 to Tier 2
Naming anything I could simplify or improve.

Hello. Recently I've been working on a pet project of mine written in C and I needed to reduce the amount of space a lookup table was taking in memory and on disk. I applied a few simple compression techniques and got a 2x space reduction. I wrote this post where I describe my constraints, the techniques, and results.

https://blog.x4204.xyz/posts/compressing-lookup-tables.html

Hello everyone,

I am currently working on a (very early progress) retained-mode UI library using raylib. I might switch to SDL3 later, or try to make a CPU-only rendering engine in the far future.

Right now i'm trying to implement a multi-line text edit widget, that would be as versatile as possible, all while maintaining low memory usage. I So far my structure consists of an "original text" character array, and an array of struct representing wrapped lines.

typedef struct TextBox {
  Widget widget;
  char* text;
  int cursorX; int cursorY;
  int offsetX; int offsetY;
  TextLine* lines;
  int _lineCount;
};

At each resize, the layout is recalculated, and the lines reallocated, which I find really wasteful. However, I didn't come up with another model for text editing yet.

void TextBox_Resize(TextBox* textbox, int w, int h){
  textbox->widget.bounds.w = w;
  textbox->widget.bounds.h = h;
  textbox->_lineCount = 0;

  //Estimate text length
  int textLength = TextLength(textbox->text); //Raylib function
  int totalTextWidth = MeasureText(textbox->text, 12);
  int estimatedLineCount = (int)(totalTextWidth / w) + 1;

  //Add 1 line to the estimation for each newline
  for (int i = 0; i < textLength; i++) {
    if (textbox->text[i] == '\n') { estimatedLineCount++; }
  }

  printf("Estimating %d lines for resize\n", estimatedLineCount);

  //free(textbox->lines);
  textbox->lines = realloc(textbox->lines, estimatedLineCount * sizeof(TextLine));

  Font font = GetFontDefault(); //Will be replaced after

  int currentLine = 0;
  int lineStart = 0;
  int lineEnd = 0;

  float currentGlyphWidth = 0;
  float totalLineWidth = 0;

  // Almost copied from raylib example
  for (int i = 0; i < textLength; i++){
    //printf("Current byte %d\n", i);
    int codepointByteCount = 0;

    // Gets UTF8 codepoints instead of simply bytes.
    int codepoint = GetCodepoint(&textbox->text[i], &codepointByteCount);
    //printf("Got codepoint %d, is %c\n", codepoint, codepoint);
    int glyphIndex = GetGlyphIndex(font, codepoint);
    //printf("Got index %d\n", index);

    // We are advancing more than 1 byte at a time if we get UTF-8 text.
    // Since the default font is limited, replace invalid codepoints with
    // "?" and keep advancing 1 byte at a time.
    if (codepoint == 0x3f) codepointByteCount = 1;
    i += (codepointByteCount - 1); // i will advance by itself in next iter, dont accumulate offsets.

    currentGlyphWidth = GetGlyphAtlasRec(GetFontDefault(), codepoint).width;
    //printf("Glyph width is %f\n", currentGlyphWidth);
    totalLineWidth += currentGlyphWidth;

    //printf("Total line length is %f\n", totalLineWidth);

    // Follow line
    lineEnd = i;

    if (totalLineWidth >= textbox->widget.bounds.w || codepoint == '\n' || codepoint == 0) {
      printf("line is %f pixels wide\n", totalLineWidth);
      textbox->lines[currentLine].text = calloc((lineEnd - lineStart),  sizeof(char));
      textbox->lines[currentLine].text = strncpy(textbox->lines[currentLine].text, textbox->text + lineStart, (lineEnd - lineStart));

      // Set last char of text to null
      textbox->lines[currentLine].text[lineEnd - lineStart] = '\0';
      lineStart = (codepoint == '\n' ? lineEnd + 1 : lineEnd);

      totalLineWidth = 0;
    } else {
      lineStart = lineEnd; lineEnd = textLength;
    }

    textbox->lines[currentLine].text[lineEnd - lineStart] = '\0';
    currentLine++; textbox->_lineCount++;
  }
}

Are there any articles / projects with clever approaches to text editing, that keep a low memory footprint ?
Thanks for your advice !

Can someone recommend/send some resources for advanced and trickey c questions. I have my placement exam in a week ans most of it is dominated by c. The mock had questions related to struct padding, macros, increment decrements, static, volatile, unsigned signed ints and some other tricky things. I’m familier with the topics, but where can I practice the trickey questions?

I've been working in C and assembly for 3 years now (consistently) and I've noticed a trend. The more I work on C or do C adjacent activities like decompiling assembly, the quicker I forget how the stack and heap works.

And the level of forgetting is always proportional to how complicated the project I'm working on is. A basic project? Probably won't forget. An intermediary project? I'll need to Google "Stack vs Heap" at least once. Advanced project? I'll need to start from scratch and watch a YouTube video a couple of times to remember.

Does anyone else have this amnesia or is it just me?

i made logging in C that does not need formater% as printf instead it has auto-type detect via _Generic ,like fmt it uses {} as placeholder

i started it just for fun but later i notice that it is insanely fast it beets fmt lib and rust print 4.5x faster

it uses linux syscall write i might map syscall for windows latter

this is very interesting because i did not optimize the lib like convert from type to another use poor impl + i write in the buffer many times

write(1, logtag, strlen(logtag));

write(1, filename, strlen(filename)) ;

write(1, "->", 2);

write(1, function, strlen(function)) ;

write(1, " ", 1);

write(1, buffer, out);

so i guess after optimizing it will be 2x faster

all respect for fmt devs i inspired the {} from them btw

Pls help me idk what's going on...
https://imgur.com/a/5KLsigY

It complains that it can't find the pow function.

Editor is an extremely simple-to-use terminal text editor. Written in C using only native POSIX libraries/api, it offers simplicity while being very responsive and performant. Editor was inspired by and written using antirez's kilo editor tutorial.

Source: https://github.com/111nation/Editor/

This tutorial was such a blast, and it walks you through how to make your own text editor. I highly recommend you give it a look!

~ chlo

Hey guys, I just finished the mandatory part of ft_printf and I'm ready to tackle the bonuses, but I'm not sure where to start. Do you have any tips or strategies on how to implement them? What tools or approaches worked best for you?

After my class in C programing I have decided to dig more around and one thing I found out that scanf is unsafe specially in arithmethic input? can somoe please extrapolate this one concept? Advance thanks for those who answered to my question.

golfing a SHA-256 implementation in C and ended up at 559 bytes.
Curious if anyone here can beat it.

#define S(x,a,b)(x>>a^x<<32-a^x>>b^x<<32-b^x>>
unsigned k[72],g[216],i,j,p,n,t,m,*u,*z;char*q=g;main(c,v)char**v;{for(;j<64;p-c||(j<8&&(k[j]=sqrt(c)*0x1p32),k[71-j++]=cbrt(c)*0x1p32),c++)for(p=1;c%++p;);for(;q[n^3]=v[1][n];n++);q[n^3]=128;m=n+72>>6<<4,g[m-1]=n*8;for(;t<m;t+=16)for(bcopy(g+t,z=g+64,64),bcopy(k,u=g+208,32),i=72;i--;i>7?(z[16]=*z+S(z[1],7,18)3)+z[9]+S(z[14],17,19)10),j=u[4],p=u[7]+k[i]+*z+++(S(j,6,11)25)^j<<7)+(j&u[5]^~j&u[6]),j=S(*u,2,13)22)^*u<<10,j+=*u&u[1]^(*u^u[1])&u[2],u[3]+=p,*--u=p+j):(k[i]+=u[i]));for(;++i<8;)printf("%08x",k[i]);}

My OOP library relies on it for its unspecified arguments behavior.

For example:

#define ptmethod(pt, ret_type, identifier) \
    (*((ret_type (**)()) padd(pt, identifier, ptfunction, NULL, NULL)))

#define ptapply(pt, ret_type, identifier, ...) \
    ((ret_type (*)()) pget(pt, identifier))(pt __VA_OPT__(,) __VA_ARGS__)

You could add a method to an object with:

void drive_Car(prototype *Car, double speed, double x_direction, double y_direction);

ptmethod(Car, void, "drive") = drive_Car;

and call it with

ptapply(Car, void, "drive", 1.3, 0.1, 5.0)

How do I do this in the new standard?

#include <stdio.h>


int main() {
    int s[90];
    printf("%d\n",s[43]);
}

I wanted to understand how modern AI models actually generate text, but most inference codebases are tens or hundreds of thousands of lines long. They’re incredibly impressive, but they’re optimized for flexibility and performance, not for understanding.

So I implemented a complete CPU runtime for Google’s latest open language model, Gemma 4, in about 700 lines of C.

The whole point is that you can open one file, start at main() , and follow a prompt all the way through the program. You can see every buffer that’s allocated, every mathematical operation that transforms the activations, every update to the KV cache, and every step that eventually produces the next token.

I think C is a great language for this kind of project. There’s very little hidden from you. The data structures, memory layout, SIMD kernels, and execution flow are all visible, so the implementation ends up feeling much closer to the hardware than to the diagrams in an ML paper.

https://github.com/ryanssenn/gemma4.c

In all programming languages, there are places where you need to write a function with some parameters that are unused. Mostly to satisfy some callback signature or functional interface. But C makes it easiest of all languages. Where in other languages you have to give the compiler hints like @SuppressWarnings("unused") or name _: String to prevent it from warning you that this parameter here is unused, in C you can just omit the parameter name:

void
foo(int arg, char*) {
    ...implemenation
}

That's it, no hints, no warnings (even with -Wextra), no nuthin'. The compiler understands that if you haven't given this parameter a name, then you intend it to be unused. This is the most concise of all languages and you don't even have to come up with a (useless) name.

link to code : https://github.com/RamiBrahimi-c/big-ar9am .

hello i am sharing with you project i did this summer , in fact it is a side project was done to be included in another side project which is a crypto lib in C and it is important to say that it is not meant for professional use at all (code : https://github.com/RamiBrahimi-c/cryptography-library ) .

the crypto lib was asked for us to do in a uni class , and due to the fact that i was not able to take my full time with it , like actually doing everything myself from scratch and not vibecode it or use openssl and GMP , so i had to kind of rely on them a little just until the deadline was over and i got marked for it , then i decided to go back to it and make it totally from the ground up .

the crypto lib has :

• hash functions ( sha256 , sha512 , md4 , md5 )
• classic ciphers ( affine , cesar , ..etc )
• symmetric ones ( aes , des , rc4 , blowfish , .. )
• asymmetric ones that requires arbitary length numbers in protocols like rsa , elgamel , and defil-hellman .

for now all of them except the asymmetric crypto were done from the ground up , i even tried not to copy block of constants if i could calculate it manually ( like the AES s-box that i generated manually by calculating it with galois fields operations in 2⁸ ) , that being said i refused to also rely on GMP to do all the calculations for me too and here where this project was born .

for now it has several features like basic arithmetic operations and even prime numbers testing , generation , finding inverse multiplicative too .. etc you can check my readme ,

yet it is also important that it is not optimized yet , i must note that it will be subjective and based on what i feel like either to go further and see how things like Karatsuba , FFT‑based (Schönhage‑Strassen) , Newton‑Raphson division , ..etc .
although it feels really interesting to see all these mentioned algorithms in action .

an other important point imo is how did i make sure it is at least calculating right , and for that i used Python 3.12.3 , it was extremily helpful and i absolutely appreciate such things like this .

and that would be it , i apologize if i drifted on the main subject i wanted to give the full picture of things , also you can read the README of both of my projects for more details especially the readme of this big num library ( i promise ai just helped with technical details , otherwise it is completely mine )

NOTE : if you want to ask about the why i did what i did , i dont have a clear answer , cuz i love to know how things work and why ? cuz i just want to make my own stuff ? for fun ?
idk , could be one of these could be all of them .

let me know your thoughts ,