23.3.4 Naming macros

Just like functions in a C program, it's important to choose a good name for your Autoconf macros. A well-chosen name helps to unambiguously describe the purpose of the macro. Macros in M4 are all named within a single namespace and, thus, it is necessary to follow a convention to ensure that names retain uniqueness. This reasoning goes beyond just avoiding collisions with other macros--if you happen to choose a name that is already known to M4 as a definition of any kind, your macro's name could be rewritten by the prior definition during macro processing.

One naming convention has emerged--prefixing each macro name with the name of the package that the macro originated in or the initials of the macro's author. Macros are usually named in a hierarchical fashion, with each part of the name separated by underscores. As you move left-to-right through each component of the name, the description becomes more detailed. There are some high-level categories of macros suggested by the Autoconf manual that you may wish to use when forming a descriptive name for your own macro. For example, if your macro tries to discover the existence of a particular C structure, you might wish to use C and STRUCT as components of its name.

`C'

Tests related to constructs of the C programming language.

`DECL'

Tests for variable declarations in header files.

`FUNC'

Tests for functions present in (or absent from) libraries.

`HEADER'

Tests for header files.

`LIB'

Tests for libraries.

`PATH'

Tests to discover absolute filenames (especially programs).

`PROG'

Tests to determine the base names of programs.

`STRUCT'

Tests for definitions of C structures in header files.

`SYS'

Tests for operating system features, such as restartable system calls.

`TYPE'

Tests for built-in or declared C data types.

`VAR'

Tests for C variables in libraries.

Some examples of macro names formed in this way include:

`AC_PROG_CC'

A test that looks for a program called cc.

`AC_C_INLINE'

A test that discovers if the C keyword inline is recognized.

`bje_CXX_MUTABLE'

A test, written by "bje", that discovers if the C++ keyword mutable is recognized.