[PATCH v2] fread.3: Add example

[PATCH v2] fread.3: Add example

[Arkadiusz Drabczyk]

Signed-off-by: Arkadiusz Drabczyk <arkadiusz@drabczyk.org>
---
 man3/fread.3 | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 55 insertions(+)

diff --git a/man3/fread.3 b/man3/fread.3
index 2dd7be9..4af3850 100644
--- a/man3/fread.3
+++ b/man3/fread.3
@@ -113,6 +113,61 @@ 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: 0x02
+.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, sizeof(buffer) / sizeof(*buffer), sizeof(*buffer),
+              fp);
+    if (ret != sizeof(*buffer)) {
+        fprintf(stderr, "fread() failed: %zu\en", ret);
+        exit(EXIT_FAILURE);
+    }
+
+    printf("ELF magic: %#04x%02x%02x%02x\en", buffer[0], buffer[1],
+           buffer[2], buffer[3]);
+
+    ret = fread(buffer, 1, 1, fp);
+    if (ret != 1) {
+        fprintf(stderr, "fread() failed: %zu\en", ret);
+        exit(EXIT_FAILURE);
+    }
+
+    printf("Class: %#04x\en", buffer[0]);
+
+    fclose(fp);
+
+    exit(EXIT_SUCCESS);
+}
+.EE
 .SH SEE ALSO
 .BR read (2),
 .BR write (2),
-- 
2.9.0

Re: [PATCH v2] fread.3: Add example

[Michael Kerrisk (man-pages)]

Hello Arkadiusz,

On 6/18/20 4:22 PM, Arkadiusz Drabczyk wrote:
> Signed-off-by: Arkadiusz Drabczyk <arkadiusz@drabczyk.org>

Thanks! Patch applied. One glitch below edited.

> ---
>  man3/fread.3 | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 55 insertions(+)
> 
> diff --git a/man3/fread.3 b/man3/fread.3
> index 2dd7be9..4af3850 100644
> --- a/man3/fread.3
> +++ b/man3/fread.3
> @@ -113,6 +113,61 @@ 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

I removed the preceding line (which did not render, and I assume was
cruft you meant to delete).


Thanks,

Michael

> +ELF magic: 0x7f454c46
> +Class: 0x02
> +.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, sizeof(buffer) / sizeof(*buffer), sizeof(*buffer),
> +              fp);
> +    if (ret != sizeof(*buffer)) {
> +        fprintf(stderr, "fread() failed: %zu\en", ret);
> +        exit(EXIT_FAILURE);
> +    }
> +
> +    printf("ELF magic: %#04x%02x%02x%02x\en", buffer[0], buffer[1],
> +           buffer[2], buffer[3]);
> +
> +    ret = fread(buffer, 1, 1, fp);
> +    if (ret != 1) {
> +        fprintf(stderr, "fread() failed: %zu\en", ret);
> +        exit(EXIT_FAILURE);
> +    }
> +
> +    printf("Class: %#04x\en", buffer[0]);
> +
> +    fclose(fp);
> +
> +    exit(EXIT_SUCCESS);
> +}
> +.EE
>  .SH SEE ALSO
>  .BR read (2),
>  .BR write (2),
> 


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/