add option parsing

meson.build

@@ -11,10 +11,12 @@ project(
 sources = [
   'src/image.c',
   'src/main.c',
+  'src/options.c',
   'src/ppm.c',
 ]
 
 executable(
   'buddhabrot',
   sources : sources,
+  c_args : '-D_XOPEN_SOURCE',
 )

src/main.c

@@ -3,6 +3,7 @@
 #include <stdlib.h>
 
 #include "image.h"
+#include "options.h"
 #include "ppm.h"
 
 static void fill_image(struct image *image) {
@@ -16,13 +17,17 @@ static void fill_image(struct image *image) {
     }
 }
 
-int main(void) {
-    struct image *image = create_image(960, 540);
+int main(int argc, char *argv[]) {
+    struct options opt = parse_options(&argc, &argv);
+
+    struct image *image = create_image(opt.w, opt.h);
     if (!image)
         err(EXIT_FAILURE, "could not allocate image");
 
     fill_image(image);
-    print_ppm(image, stdout);
+    print_ppm(image, opt.output);
+
+    fclose(opt.output);
     destroy_image(image);
 
     return EXIT_SUCCESS;

src/options.c

@@ -0,0 +1,43 @@
+#include "options.h"
+
+#include <err.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+struct options parse_options(int *argc, char **argv[]) {
+    struct options opts = {
+        .output = stdout,
+        .w = 960,
+        .h = 540,
+    };
+
+    opterr = 0; // Deactivate error message from `getopt`
+
+    int opt;
+    while ((opt = getopt(*argc, *argv, "h:o:w:")) != -1) {
+        switch (opt) {
+        case 'h':
+            if (!sscanf(optarg, "%zu", &opts.h))
+                errx(EXIT_FAILURE, "could not parse height");
+            break;
+        case 'o':
+            if (!freopen(optarg, "w", opts.output))
+                err(EXIT_FAILURE, "could not open output file");
+            break;
+        case 'w':
+            if (!sscanf(optarg, "%zu", &opts.w))
+                errx(EXIT_FAILURE, "could not parse width");
+            break;
+        default:
+            fprintf(stderr, "Usage: %s [-o FILE] [-h HEIGHT] [-w WIDTH]\n",
+                    (*argv)[0]);
+            exit(EXIT_FAILURE);
+        }
+    }
+
+
+    *argc -= optind;
+    *argv += optind;
+
+    return opts;
+}

src/options.h

@@ -0,0 +1,15 @@
+#ifndef OPTIONS_H
+#define OPTIONS_H
+
+#include <stddef.h>
+#include <stdio.h>
+
+struct options {
+    FILE *output;
+    size_t w;
+    size_t h;
+};
+
+struct options parse_options(int *argc, char **argv[]);
+
+#endif /* !OPTIONS_H */