few comments below,
hope that helps
re,
wh
________________________________________
Von: linux-man-owner@xxxxxxxxxxxxxxx [linux-man-owner@xxxxxxxxxxxxxxx] im Auftrag von Arkadiusz Drabczyk [arkadiusz@xxxxxxxxxxxx]
Gesendet: Mittwoch, 17. Juni 2020 20:45
An: mtk.manpages@xxxxxxxxx
Cc: linux-man@xxxxxxxxxxxxxxx
Betreff: [PATCH] fread.3: Add example
Signed-off-by: Arkadiusz Drabczyk <arkadiusz@xxxxxxxxxxxx>
---
man3/fread.3 | 53 +++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 53 insertions(+)
diff --git a/man3/fread.3 b/man3/fread.3
index 2dd7be9..c19a59c 100644
--- a/man3/fread.3
+++ b/man3/fread.3
@@ -113,6 +113,59 @@ T} Thread safety MT-Safe
.TE
.SH CONFORMING TO
POSIX.1-2001, POSIX.1-2008, C89.
+.SH EXAMPLES
+The program below demonstrates the use of
+.BR fread ()
+by parsing /bin/sh ELF executable in binary mode and printing its
+magic and class:
+.PP
+.in +4n
+.EX
+$ \fB./a.out\fP
+./a.out
+ELF magic: 0x7f454c46
+Class: 0x2
+.EE
+.in
+.SS Program source
+\&
+.EX
+#include <stdio.h>
+#include <stdlib.h>
+
+int
+main(void)
+{
+ FILE *fp = fopen("/bin/sh", "rb");
+ if (!fp) {
+ perror("fopen");
+ return EXIT_FAILURE;
+ }
+
+ unsigned char buffer[4];
+
+ size_t ret = fread(buffer, 4, 1, fp);
this is the core of the example and should be a bit more verbose:
maybe this is a bit to cryptic
ret = fread(buffer,sizeof (buffer)/sizeof (*buffer), sizeof (*buffer), fp);
alt:
size_of_buf= sizeof (buffer)/sizeof (*buffer);
ret = fread(buffer, // start of buffer
sizeof (buffer)/sizeof (*buffer), // size of buffer in bytes
sizeof (*buffer), // size of element
fp); // file pointer
+ if (ret != 1) {
+ fprintf(stderr, "fread() failed: %zu\en", ret);
+ exit(EXIT_FAILURE);
+ }
+
+ printf("ELF magic: %#x%x%x%x\en", buffer[0], buffer[1], buffer[2],
+ buffer[3]);
+
this works for /bin/sh but if the user plays round this may show confusing results
so you could simply do:
printf("ELF magic: %#02x%02x%02x%02x\en",
so you are consistent in all cased. (until some will test this on a big endian, no idea
what will happen then).
+ ret = fread(buffer, 1, 1, fp);
+ if (ret != 1) {
+ fprintf(stderr, "fread() failed: %zu\en", ret);
+ exit(EXIT_FAILURE);
+ }
+
please drop a line what case you want to explain here, looks like the same as above.
+ printf("Class: %#x\en", buffer[0]);
+
+ fclose(fp);
+
+ exit(EXIT_SUCCESS);
+}
+.EE
.SH SEE ALSO
.BR read (2),
.BR write (2),
--
2.9.0
