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clinuxposixstandardslanguage-lawyer
Koray Tugay
Koray Tugay

Reputation: 23854

What is included in C Standard library?

I will give an example from The GNU C Library documentation:

13.1 Opening and Closing Files

This section describes the primitives for opening and closing files using file descriptors. The open and creat functions are declared in the header file fcntl.h, while close is declared in unistd.h.

My question is:

Can unistd.h and fcntl.h be considered as Standard C? As far as I know, they should be part of the Posix standard?

Can we say C Standard Library = Posix functions + C API? I am confused because Wikipedia page for C Standard Library does not include unistd.h but the GNU C Library documentation includes it?

Upvotes: 3

Views: 3005

Answers (2)

Sourav Ghosh
Sourav Ghosh

Reputation: 134396

As far as I can see, in C11 standard, there is no unistd.h and fcntl.h. So, strictly speaking, they are not part of the C standard.

When it comes to the implementation part, the GNU C library (glibc) is one of them. From the wiki page

glibc provides the functionality required by the Single UNIX Specification, POSIX (1c, 1d, and 1j) and some of the functionality required by ISO C11, ISO C99, Berkeley Unix (BSD) interfaces, the System V Interface Definition (SVID) and the X/Open Portability Guide (XPG), Issue 4.2, with all extensions common to XSI (X/Open System Interface) compliant systems along with all X/Open UNIX extensions.

In addition, glibc also provides extensions that have been deemed useful or necessary while developing GNU.

So, as a part of the POSIX standard, they are available in glibc.

Reference: Check the C11 standard draft version here.

Upvotes: 3

Yu Hao
Yu Hao

Reputation: 122493

No, unistd.h, fcntl.h, etc, are not standard C.

In general, standard C doesn't include functions that deal with low level file manipulation. For example, fopen, fread, and fwrite are part of standard C library. While POSIX open, read, write functions are not standard C.

Upvotes: 5

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