What does the postfix "_t" stand for in C?

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+1 Q:

What does the postfix "_t" stand for in C?

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What does a type followed by _t (underscore-t) represent?

While typing in my IDE (Xcode), autocomplete pops up already-defined words when I'm partway thru entering some variable name. I occasionally see names that have '_t' at the end of them.

What naming convention is that and what does it mean?
Is there a reference document to look up pre- and post-fixes in common use?

Searching with the term "postfix" gives me a lot of GoogleNoise about the mail server of the same name.

+1 A:

based only on my own experience, the "_t" postfix means "data type". In other words, it's a datatype defined used typedef.

nairdaen 2009-09-08 00:47:06

+3 A:

The t stands for "type" or "typedef." You'll see a lot of POSIX headers (and others) with time_t, size_t, and others. These which hold (not necessarily defined) specific bit-sizes based on the operating system and machine architecture.

Sufian 2009-09-08 00:48:23

Also in standard C: size_t, wchar_t, wint_t, clock_t, not to mention the integer types such as int8_t, uint16_t, ... Actually, all the 'POSIX' types mentioned in the answer are defined first in the C standard and only secondarily in POSIX (because it uses the C standard). There are plenty of POSIX-only types ending in '_t' too: ino_t, dev_t appear in `<sys/stat.h>`, for example, and gid_t, uid_t, mode_t, and ...

Jonathan Leffler 2009-09-08 00:57:04

The "_t" suffix is a convention for data type names such as size_t or wchar_t. It's not used consistently.

John Bode 2009-09-08 00:49:53

I believe the `_t` suffix was largely POSIX, but then ANSI decided to incorporate some POSIX features as being kind of important. I can't be sure of that, but the first POSIX standard was released in 1988, so they were definitely happening around the same time.

Chris Lutz 2009-09-08 00:57:04

The first C standard was released in 1989, but was largely ready a year or two earlier as the (ANSI) C standard committee tried to get final agreement on the I18N/G11N/L10N aspects of the standard - in particular <locale.h>. But you're right - the (IEEE) POSIX and C standards were developed at very much the same time. The ISO POSIX standard was first released in 1990, the same year as ISO C, IIRC.

Jonathan Leffler 2009-09-08 01:00:53

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What does the postfix "_t" stand for in C?

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