What is the difference between malloc and malloc(3)?

Question

While reading a hacker article on the jemalloc memory manager, the hacker keeps referring to malloc(3), not malloc. I wondered why.

Does he do so because it refers to a specific linux malloc implementation? Or simply to refer to all malloc variants, that implement the interface as described on the section 3 (libary functions) of the unix/linux manual pages? This option is my guess, want to be sure. Is there a different reason?

So, is the hacker just overly specific? Or is there a difference between malloc and malloc(3)?

The (3) part is not a reference to other documentation, article or research mentioned later in the hacker article.

Some people write(2) that way all the time(2), as it makes it clear(1)er what they are trying to stat(2)e. — ChrisH, Jul 11 '12 at 23:30

score 9 · Accepted Answer · answered Jul 11 '12 at 20:24

malloc(3) is just a hint that malloc is a part of the section 3 of the man pages. The section 3 is where are the library functions. This is by opposition to the section 2 of the man pages where are the syscalls. There is no malloc(2).

For example:

fwrite is a library function so sometimes written as fwrite(3)

write is a syscall so sometimes written as write(2)

If you run the command:

$ man man

it will tell you

   1   Executable programs or shell commands
   2   System calls (functions provided by the kernel)
   3   Library calls (functions within program libraries)
   4   Special files (usually found in /dev)
   5   File formats and conventions eg /etc/passwd
   6   Games
   7   Miscellaneous  (including  macro  packages and convenâ
       tions), e.g. man(7), groff(7)
   8   System administration commands (usually only for root)
   9   Kernel routines [Non standard]

score 3 · Answer 2 · answered Jul 11 '12 at 20:26

Preface: My unix is weak.

I believe that it is simply a reference to the section 3 library.

( from the jargon file )
References such as malloc(3) and patch(1) are to Unix facilities (some of which, such as patch(1), are actually open source distributed over Usenet).

pb2q · Answer 3 · 2012-07-11T20:33:34.663

1

It looks like the author is simply being very specific.

Specifying the reference to section 3 of the man pages is often useful if there might be an e.g. shell version of the same function. For instance, man 1 printf for printf(1) vs. printf(3).

But in the case of malloc documentation should exist only in section 3.

edited Jul 11 '12 at 20:33

answered Jul 11 '12 at 20:24

pb2q

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I believe he is referring to the POSIX definition of malloc. It's not just Linux specific. – Jul 11 '12 at 20:27

What is the difference between malloc and malloc(3)?

3 Answers3