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f9fb90f299
- Update labels so they use consistent naming. Instead of the copy-and-pasted `chapter` prefix, name labels with a prefix consistent with what they point to: - "module-" for module - "target-" for targets - "docs-" for general documentation - Remove the unnecessary highlight and default-domain directives. Neither is necessary since the Pigweed docs always specify the language in code snippets and other directives. Change-Id: I55c34e9ec919f6f4670e5d3d008e0edf5fecf05b Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/19328 Commit-Queue: Wyatt Hepler <hepler@google.com> Reviewed-by: Keir Mierle <keir@google.com>
88 lines
3.2 KiB
ReStructuredText
88 lines
3.2 KiB
ReStructuredText
.. _module-pw_preprocessor:
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---------------
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pw_preprocessor
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---------------
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The preprocessor module provides various helpful preprocessor macros.
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Compatibility
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=============
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C and C++
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Headers
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=======
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The preprocessor module provides several headers.
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pw_preprocessor/arguments.h
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---------------------------------
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Defines macros for handling variadic arguments to function-like macros. Macros
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include the following:
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.. c:function:: PW_DELEGATE_BY_ARG_COUNT(name, ...)
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Selects and invokes a macro based on the number of arguments provided. Expands
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to ``<name><arg_count>(...)``. For example,
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``PW_DELEGATE_BY_ARG_COUNT(foo_, 1, 2, 3)`` expands to ``foo_3(1, 2, 3)``.
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This example shows how ``PW_DELEGATE_BY_ARG_COUNT`` could be used to log a
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customized message based on the number of arguments provided.
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.. code-block:: cpp
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#define ARG_PRINT(...) PW_DELEGATE_BY_ARG_COUNT(_ARG_PRINT, __VA_ARGS__)
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#define _ARG_PRINT_0(a) LOG_INFO("nothing!")
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#define _ARG_PRINT_1(a) LOG_INFO("1 arg: %s", a)
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#define _ARG_PRINT_2(a, b) LOG_INFO("2 args: %s, %s", a, b)
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#define _ARG_PRINT_3(a, b, c) LOG_INFO("3 args: %s, %s, %s", a, b, c)
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When used, ``ARG_PRINT`` expands to the ``_ARG_PRINT_#`` macro corresponding
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to the number of arguments.
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.. code-block:: cpp
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ARG_PRINT(); // Outputs: nothing!
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ARG_PRINT("a"); // Outputs: 1 arg: a
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ARG_PRINT("a", "b"); // Outputs: 2 args: a, b
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ARG_PRINT("a", "b", "c"); // Outputs: 3 args: a, b, c
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.. c:function:: PW_COMMA_ARGS(...)
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Expands to a comma followed by the arguments if any arguments are provided.
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Otherwise, expands to nothing. If the final argument is empty, it is omitted.
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This is useful when passing ``__VA_ARGS__`` to a variadic function or template
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parameter list, since it removes the extra comma when no arguments are
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provided. ``PW_COMMA_ARGS`` must NOT be used when invoking a macro from
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another macro.
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For example. ``PW_COMMA_ARGS(1, 2, 3)``, expands to ``, 1, 2, 3``, while
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``PW_COMMA_ARGS()`` expands to nothing. ``PW_COMMA_ARGS(1, 2, )`` expands to
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``, 1, 2``.
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pw_preprocessor/boolean.h
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-------------------------
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Defines macros for boolean logic on literal 1s and 0s. This is useful for
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situations when a literal is needed to build the name of a function or macro.
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pw_preprocessor/compiler.h
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--------------------------
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Macros for compiler-specific features, such as attributes or builtins.
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pw_preprocessor/concat.h
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------------------------
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Defines the ``PW_CONCAT(...)`` macro, which expands its arguments if they are
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macros and token pastes the results. This can be used for building names of
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classes, variables, macros, etc.
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pw_preprocessor/util.h
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----------------------
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General purpose, useful macros.
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* ``PW_ARRAY_SIZE(array)`` -- calculates the size of a C array
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* ``PW_UNUSED(value)`` -- silences "unused variable" compiler warnings
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* ``PW_STRINGIFY(...)`` -- expands its arguments as macros and converts them to
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a string literal
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* ``PW_EXTERN_C`` -- declares a name to be ``extern "C"`` in C++; expands to
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nothing in C
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* ``PW_EXTERN_C_START`` / ``PW_EXTERN_C_END`` -- declares an ``extern "C" { }``
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block in C++; expands to nothing in C
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