cannot write a number to disk file in its binary format?

[lichtjiang]

For example, say we want to write integer "100" in a binary file, "test.dat". The following code won't work.

$anumber=100;
$file="test.dat";
open(DAT, ">", $file);
print DAT $anumber;

This will write 3 bytes in "test.dat" as 31, 30, and 30. Though, if $anumber is read as "64" in hex from a binary file, then "64" can be written to "test.dat" in 1 byte.

It seems a scalar variable only writes its string value to disk file. Why? Any idea how to write a number's native value into a binary disk file? Thanks!

 

[hoinz]

chr function is what you need:
$anumber=chr(100);

 

[lichtjiang]

Thanks a lot!

 

[lichtjiang]

chr() can only work on a number that is of size of 1 byte. What about a number that takes more than 1 byte, say 1000. How to ensure this number is written to a binary file in 2 bytes?

 

[hoinz]

I think you will have to split it up yourself:
1000 = 3*256 + 232
and so: chr(3), chr(232)

 

[lichtjiang]

Thanks. That's also what I thought or maybe someone has done thiss before ...

 

[lichtjiang]

though I think chr() can be very generic. but the problem can be better handled by "pack(...)" function, which is purposedly designed for writing binary data I guess.