What does the postfix "_t" stand for in C? [duplicate]

Question

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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.

1. What naming convention is that and what does it mean?

2. 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.

Haiti

Duplicate: #232260 – Bearce

This is a two-part question but everyone is getting hung up on the first part. – Haiti

edited question to make that more clear. – Haiti

The second part can be answered by "C Standard" and POSIX (see opengroup.org/onlinepubs/9699919799/toc.htm) and your system manual pages. AFAICR, Microsoft doesn't use the '_t' convention in its own code except when following a standard (or, at least, it is not as pervasive a convention in Windows as it is in the Unix/Linux world). – Catercorner

Fastest closers in the west :( – Haiti

The POSIX standard reserves names ending '_t' when you include POSIX headers. I don't think there are any widespread prefix conventions; people use a few characters, often but not necessarily followed by an underscore, to generate their own namespace. See the Apache Portable Runtime (apr - apr.apache.org) library for examples; see also ICU (icu-project.org) for more examples, and (in C++) the Boost (boost.org) libraries. – Catercorner

Answer 1

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.

Oilla

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 ... – Catercorner

Answer 2

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

Holograph

Answer 3

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

Wort

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. – Brand

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. – Catercorner