c.tmd

---
title: Tmdoc - examples for the C programming language
author: Detlef Groth
date: 2025-10-17 20:00
include-before: |
    <style>
    body { max-width: 1000px; font-family: Candara, sans-serif; }
    pre  { font-family: Consolas; monospaced; }
    table { min-width: 400px; border-spacing: 5px;  border-collapse: collapse; }
    </style>
    <center>some links on top</center>
---

`tcl include header.md`

## Introduction

Below are some C coding examples.

## Hello World

```{.shell cmd="gcc %i -o hello&&./hello > %o" chunk.ext=c ext=txt}
#include <stdio.h>
int main() {
    printf("Hello C World!\n");
    return(0);
}
```

## Image Creation

Here   an    example    which    does    create    an    image    using    the
[Gd](https://libgd.github.io) library.

```{.shell label=gdtest cmd="gcc -L/usr/lib/x86_64-linux-gnu %i -o %b -lgd -lpng -lz -ljpeg -lfreetype -lm &&./%b %o" chunk.ext=c ext=png include=false}
/* Bring in gd library functions */
#include <gd.h>

/* Bring in standard I/O so we can output the PNG to a file */
#include <stdio.h>


int main(int argc, char **argv) {
  /* Declare the image */
  gdImagePtr im;
  /* Declare output files */
  FILE *pngout;
  /* Declare color indexes */
  int black;
  int white;

  /* Allocate the image: 64 pixels across by 64 pixels tall */
  im = gdImageCreate(64, 64);

  /* Allocate the color black (red, green and blue all minimum).
    Since this is the first color in a new image, it will
    be the background color. */
  black = gdImageColorAllocate(im, 0, 0, 0);

  /* Allocate the color white (red, green and blue all maximum). */
  white = gdImageColorAllocate(im, 255, 255, 255);

  /* Draw a line from the upper left to the lower right,
    using white color index. */
  gdImageLine(im, 0, 0, 63, 63, white);

  /* Open a file for writing. "wb" means "write binary", important
    under MSDOS, harmless under Unix. */
  pngout = fopen(argv[1], "wb");

  /* Output the image to the disk file in PNG format. */
  gdImagePng(im, pngout);

  /* Close the files. */
  fclose(pngout);

  /* Destroy the image in memory. */
  gdImageDestroy(im);
}
```

![](gdtest.png)

And here an example using the small PlutoVG vector graphics library which can be installed on Fedora like this:

```
sudo dnf install plutovg-devel
```

Here example code:

```
'``{.shell  cmd="gcc -lplutovg %i -o smiley&&./smiley" chunk.ext=c ext=png include=false}
... Code ...
'``
```

On debian the library seems not to be available. Here you can then install the library like this:

```
git clone https://github.com/sammycage/plutovg.git
cd plutovg
cmake -B build .
cmake --build build
sudo cmake --install build
```

You the need to use the following chunk parameters to use the package:

```
label=smiley cmd="gcc -I/usr/local/include/plutovg %i /usr/local/lib64/libplutovg.a \
    -o %b -lm &&./%b %o" chunk.ext=c ext=png include=false
```    


And here the output:

```{.shell label=smiley cmd="gcc -I/usr/local/include/plutovg %i /usr/local/lib64/libplutovg.a -o %b -lm &&./%b %o" chunk.ext=c ext=png include=false}
#include <plutovg/plutovg.h>

int main(int argc, char **argv)
{
    const int width = 150;
    const int height = 150;

    const float center_x = width / 2.f;
    const float center_y = height / 2.f;
    const float face_radius = 70;
    const float mouth_radius = 50;
    const float eye_radius = 10;
    const float eye_offset_x = 25;
    const float eye_offset_y = 20;
    const float eye_x = center_x - eye_offset_x;
    const float eye_y = center_y - eye_offset_y;

    plutovg_surface_t* surface = plutovg_surface_create(width, height);
    plutovg_canvas_t* canvas = plutovg_canvas_create(surface);

    plutovg_canvas_save(canvas);
    plutovg_canvas_arc(canvas, center_x, center_y, face_radius, 0, PLUTOVG_TWO_PI, 0);
    plutovg_canvas_set_rgb(canvas, 1, 0.8, 0);
    plutovg_canvas_fill_preserve(canvas);
    plutovg_canvas_set_rgb(canvas, 0, 0, 0);
    plutovg_canvas_set_line_width(canvas, 5);
    plutovg_canvas_stroke(canvas);
    plutovg_canvas_restore(canvas);

    plutovg_canvas_save(canvas);
    plutovg_canvas_arc(canvas, eye_x, eye_y, eye_radius, 0, PLUTOVG_TWO_PI, 0);
    plutovg_canvas_arc(canvas, center_x + eye_offset_x, eye_y, eye_radius, 0, PLUTOVG_TWO_PI, 0);
    plutovg_canvas_set_rgb(canvas, 0, 0, 0);
    plutovg_canvas_fill(canvas);
    plutovg_canvas_restore(canvas);

    plutovg_canvas_save(canvas);
    plutovg_canvas_arc(canvas, center_x, center_y, mouth_radius, 0, PLUTOVG_PI, 0);
    plutovg_canvas_set_rgb(canvas, 0, 0, 0);
    plutovg_canvas_set_line_width(canvas, 5);
    plutovg_canvas_stroke(canvas);
    plutovg_canvas_restore(canvas);

    plutovg_surface_write_to_png(surface, argv[1]);
    plutovg_canvas_destroy(canvas);
    plutovg_surface_destroy(surface);
    return 0;
}
```

![](smiley.png)