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List:       linux-man
Subject:    [patch] vcs.4: broken example code
From:       Mattias =?ISO-8859-1?Q?Engdeg=E5rd?= <mattiase () acm ! org>
Date:       2018-06-25 15:56:21
Message-ID: b48cb8b5ef9b06aba98c2b5b7609c8189a111a0c.camel () acm ! org
[Download RAW message or body]

Fix broken example code in the vcs.4 man page:

- use of wrong variable (attrib, which is uninitialised, instead of s)
- variable ch too narrow
- printing a font char index with %c, as if it were ASCII (it's not)
- removing the high font bit while changing the background colour

Also be friendly and use SEEK_* instead of numbers.


diff --git a/man4/vcs.4 b/man4/vcs.4
index aebe8cfda..c8b8cf361 100644
--- a/man4/vcs.4
+++ b/man4/vcs.4
@@ -140,7 +140,8 @@ main(void)
     struct {unsigned char lines, cols, x, y;} scrn;
     unsigned short s;
     unsigned short mask;
-    unsigned char ch, attrib;
+    unsigned char attrib, a;
+    int ch;
 
     fd = open(console, O_RDWR);
     if (fd < 0) {
@@ -158,16 +159,16 @@ main(void)
         exit(EXIT_FAILURE);
     }
     (void) read(fd, &scrn, 4);
-    (void) lseek(fd, 4 + 2*(scrn.y*scrn.cols + scrn.x), 0);
+    (void) lseek(fd, 4 + 2*(scrn.y*scrn.cols + scrn.x), SEEK_SET);
     (void) read(fd, &s, 2);
     ch = s & 0xff;
-    if (attrib & mask)
+    if (s & mask)
         ch |= 0x100;
     attrib = ((s & ~mask) >> 8);
-    printf("ch=\(aq%c\(aq attrib=0x%02x\\n", ch, attrib);
-    attrib ^= 0x10;
-    (void) lseek(fd, \-1, 1);
-    (void) write(fd, &attrib, 1);
+    printf("ch=0x%03x attrib=0x%02x\\n", ch, attrib);
+    a = (s >> 8) ^ 0x10;
+    (void) lseek(fd, \-1, SEEK_CUR);
+    (void) write(fd, &a, 1);
     exit(EXIT_SUCCESS);
 }
 .EE

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