I am interested to know the valid values which I can expect for a file descriptor.
Please let me explain a bit. I know that, for instance, when I use #include <unistd.h> on my linux system then a call to open a file for reading:
int fileDescriptor;
fileDescriptor = open("/some/filename",O_RDONLY);
an error might occur and I receive -1 as a result.
Incidently the (-1) negative one must have somewhat of a special meaning. Is it that all other values are valid file descriptors? i.e. also negative ones like -2 and -1023?
Assuming that int is 4 bytes (sizeof(int)==4), then would
(-1) = 10000000 0000000 00000000 00000001
would be the only detectable invalid file descriptor? Would others like:
(0) = 00000000 0000000 00000000 00000000(-2) = 10000000 0000000 00000000 00000010(2) = 00000000 0000000 00000000 00000010be ok? Since the file descriptor could store 4 bytes I could have therefore a maximum of (2^(8*4)-1) valid file descriptors and consequently this would be the maximum number of files I can have open, correct?
To put it plain again:
What should I expect a (valid) file descriptor to be?
any value but -1?
From the man page:
open()returns a file descriptor, a small, nonnegative integer.
and then:
open()andcreat()return the new file descriptor, or -1 if an error occurred
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