1 // Copyright 2015 The Chromium Authors
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
5 #ifndef BUILD_BUILDFLAG_H_
6 #define BUILD_BUILDFLAG_H_
8 // These macros un-mangle the names of the build flags in a way that looks
9 // natural, and gives errors if the flag is not defined. Normally in the
10 // preprocessor it's easy to make mistakes that interpret "you haven't done
11 // the setup to know what the flag is" as "flag is off". Normally you would
12 // include the generated header rather than include this file directly.
14 // This is for use with generated headers. See build/buildflag_header.gni.
16 // This dance of two macros does a concatenation of two preprocessor args using
17 // ## doubly indirectly because using ## directly prevents macros in that
18 // parameter from being expanded.
19 #define BUILDFLAG_CAT_INDIRECT(a, b) a ## b
20 #define BUILDFLAG_CAT(a, b) BUILDFLAG_CAT_INDIRECT(a, b)
22 // Accessor for build flags.
24 // To test for a value, if the build file specifies:
28 // Then you would check at build-time in source code with:
30 // #include "foo_flags.h" // The header the build file specified.
32 // #if BUILDFLAG(ENABLE_FOO)
36 // There will no #define called ENABLE_FOO so if you accidentally test for
37 // whether that is defined, it will always be negative. You can also use
38 // the value in expressions:
40 // const char kSpamServerName[] = BUILDFLAG(SPAM_SERVER_NAME);
42 // Because the flag is accessed as a preprocessor macro with (), an error
43 // will be thrown if the proper header defining the internal flag value has
45 #define BUILDFLAG(flag) (BUILDFLAG_CAT(BUILDFLAG_INTERNAL_, flag)())
47 #endif // BUILD_BUILDFLAG_H_