isfdtype - test file type of a file descriptor
The isfdtype() function returns 1 if the file descriptor
fd is of type
fdtype and 0 if it is not. On error, -1 is returned and
errno is set to indicate the cause.
The isfdtype() function is not specified in any standard, but did appear in the draft POSIX.1g standard. It is present on OpenBSD and Tru64 UNIX (where the required header file in both cases is just
<sys/stat.h>, as shown in the POSIX.1g draft), and possibly other systems.
Portable applications should use fstat(3) instead.
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