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48 lines
1.7 KiB
C
48 lines
1.7 KiB
C
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// Copyright 2015 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef BUILD_BUILDFLAG_H_
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#define BUILD_BUILDFLAG_H_
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// These macros un-mangle the names of the build flags in a way that looks
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// natural, and gives errors if the flag is not defined. Normally in the
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// preprocessor it's easy to make mistakes that interpret "you haven't done
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// the setup to know what the flag is" as "flag is off". Normally you would
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// include the generated header rather than include this file directly.
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//
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// This is for use with generated headers. See build/buildflag_header.gni.
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// This dance of two macros does a concatenation of two preprocessor args using
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// ## doubly indirectly because using ## directly prevents macros in that
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// parameter from being expanded.
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#define BUILDFLAG_CAT_INDIRECT(a, b) a ## b
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#define BUILDFLAG_CAT(a, b) BUILDFLAG_CAT_INDIRECT(a, b)
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// Accessor for build flags.
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//
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// To test for a value, if the build file specifies:
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//
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// ENABLE_FOO=true
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//
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// Then you would check at build-time in source code with:
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//
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// #include "foo_flags.h" // The header the build file specified.
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//
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// #if BUILDFLAG(ENABLE_FOO)
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// ...
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// #endif
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//
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// There will no #define called ENABLE_FOO so if you accidentally test for
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// whether that is defined, it will always be negative. You can also use
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// the value in expressions:
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//
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// const char kSpamServerName[] = BUILDFLAG(SPAM_SERVER_NAME);
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//
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// Because the flag is accessed as a preprocessor macro with (), an error
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// will be thrown if the proper header defining the internal flag value has
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// not been included.
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#define BUILDFLAG(flag) (BUILDFLAG_CAT(BUILDFLAG_INTERNAL_, flag)())
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#endif // BUILD_BUILDFLAG_H_
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