[hackers] [farbfeld] Update example in farbfeld.5 || FRIGN

[git]

commit b52f376a0f18db0dc8b2c8707cf3f41d32fd9a10
Author:     FRIGN <d...@frign.de>
AuthorDate: Tue Jan 5 11:10:39 2016 +0100
Commit:     FRIGN <d...@frign.de>
CommitDate: Tue Jan 5 11:10:39 2016 +0100

    Update example in farbfeld.5
    
    We were close to a full program anyway, so I just completed the code so
    you can study and run it easily.

diff --git a/farbfeld.5 b/farbfeld.5
index 74bd02c..2ed3354 100644
--- a/farbfeld.5
+++ b/farbfeld.5
@@ -45,8 +45,8 @@ and inherent complexity involved in handling common image 
formats
 (PNG, JPEG, GIF,...), having to rely on bloated libraries not being able
 to focus on the task at hand for a given problem.
 .Sh EXAMPLES
-Below is an example for a color inverter. No external libraries other
-than libc are needed to read the image data:
+Below is an example for a color inverter usable in a pipeline. No external
+libraries other than libc are needed to handle the image data:
 .Bd -literal -offset left
 #include <arpa/inet.h>
 
@@ -55,49 +55,58 @@ than libc are needed to read the image data:
 #include <stdlib.h>
 #include <string.h>
 
-(...)
+int
+main(int argc, char *argv[])
+{
+       uint32_t width, height, i, j, k;
+       uint16_t rgba[4];
+       uint8_t hdr[strlen("farbfeld") + 2 * sizeof(uint32_t)];
 
-uint32_t width, height, i, j, k;
-uint16_t rgba[4];
-uint8_t hdr[strlen("farbfeld") + 2 * sizeof(uint32_t)];
+       if (argc > 1) {
+               fprintf(stderr, "usage: %s\\n", argv[0]);
+               exit(1);
+       }
 
-if (fread(hdr, 1, sizeof(hdr), infile) != sizeof(hdr)) {
-       fprintf(stderr, "incomplete header\\n");
-       exit(1);
-}
-if (memcmp("farbfeld", hdr, strlen("farbfeld"))) {
-       fprintf(stderr, "invalid magic\\n");
-       exit(1);
-}
-width = ntohl(*((uint32_t *)(hdr + 8)));
-height = ntohl(*((uint32_t *)(hdr + 12)));
+       if (fread(hdr, 1, sizeof(hdr), stdin) != sizeof(hdr)) {
+               fprintf(stderr, "incomplete header\\n");
+               exit(1);
+       }
+       if (memcmp("farbfeld", hdr, strlen("farbfeld"))) {
+               fprintf(stderr, "invalid magic\\n");
+               exit(1);
+       }
+       width = ntohl(*((uint32_t *)(hdr + 8)));
+       height = ntohl(*((uint32_t *)(hdr + 12)));
 
-if (fwrite(hdr, 1, sizeof(hdr), outfile) != sizeof(hdr)) {
-       fprintf(stderr, "write error\\n");
-       exit(1);
-}
+       if (fwrite(hdr, 1, sizeof(hdr), stdout) != sizeof(hdr)) {
+               fprintf(stderr, "write error\\n");
+               exit(1);
+       }
 
-for (i = 0; i < height; i++) {
-       for (j = 0; j < width; j++) {
-               if (fread(rgba, sizeof(uint16_t), 4, infile) != 4) {
-                       fprintf(stderr, "unexpected EOF\\n");
-                       exit(1);
-               }
-               for (k = 0; k < 4; k++) {
-                       rgba[k] = ntohs(rgba[k]);
-               }
+       for (i = 0; i < height; i++) {
+               for (j = 0; j < width; j++) {
+                       if (fread(rgba, sizeof(uint16_t), 4,
+                                 stdin) != 4) {
+                               fprintf(stderr, "unexpected EOF\\n");
+                               exit(1);
+                       }
+                       for (k = 0; k < 4; k++) {
+                               rgba[k] = ntohs(rgba[k]);
+                       }
 
-               /* invert colors */
-               rgba[0] = 65535 - rgba[0];
-               rgba[1] = 65535 - rgba[1];
-               rgba[2] = 65535 - rgba[2];
+                       /* invert colors */
+                       rgba[0] = 65535 - rgba[0];
+                       rgba[1] = 65535 - rgba[1];
+                       rgba[2] = 65535 - rgba[2];
 
-               for (k = 0; k < 4; k++) {
-                       rgba[k] = htons(rgba[k]);
-               }
-               if (fwrite(rgba, sizeof(uint16_t), 4, outfile) != 4) {
-                       fprintf(stderr, "write error\\n");
-                       exit(1);
+                       for (k = 0; k < 4; k++) {
+                               rgba[k] = htons(rgba[k]);
+                       }
+                       if (fwrite(rgba, sizeof(uint16_t), 4,
+                                  stdout) != 4) {
+                               fprintf(stderr, "write error\\n");
+                               exit(1);
+                       }
                }
        }
 }