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Diffstat (limited to 'third_party/libwebrtc/build/buildflag.h')
| -rw-r--r-- | third_party/libwebrtc/build/buildflag.h | 47 |
1 files changed, 47 insertions, 0 deletions
diff --git a/third_party/libwebrtc/build/buildflag.h b/third_party/libwebrtc/build/buildflag.h new file mode 100644 index 0000000000..5776a754c4 --- /dev/null +++ b/third_party/libwebrtc/build/buildflag.h @@ -0,0 +1,47 @@ +// Copyright 2015 The Chromium Authors. All rights reserved. +// Use of this source code is governed by a BSD-style license that can be +// found in the LICENSE file. + +#ifndef BUILD_BUILDFLAG_H_ +#define BUILD_BUILDFLAG_H_ + +// These macros un-mangle the names of the build flags in a way that looks +// natural, and gives errors if the flag is not defined. Normally in the +// preprocessor it's easy to make mistakes that interpret "you haven't done +// the setup to know what the flag is" as "flag is off". Normally you would +// include the generated header rather than include this file directly. +// +// This is for use with generated headers. See build/buildflag_header.gni. + +// This dance of two macros does a concatenation of two preprocessor args using +// ## doubly indirectly because using ## directly prevents macros in that +// parameter from being expanded. +#define BUILDFLAG_CAT_INDIRECT(a, b) a ## b +#define BUILDFLAG_CAT(a, b) BUILDFLAG_CAT_INDIRECT(a, b) + +// Accessor for build flags. +// +// To test for a value, if the build file specifies: +// +// ENABLE_FOO=true +// +// Then you would check at build-time in source code with: +// +// #include "foo_flags.h" // The header the build file specified. +// +// #if BUILDFLAG(ENABLE_FOO) +// ... +// #endif +// +// There will no #define called ENABLE_FOO so if you accidentally test for +// whether that is defined, it will always be negative. You can also use +// the value in expressions: +// +// const char kSpamServerName[] = BUILDFLAG(SPAM_SERVER_NAME); +// +// Because the flag is accessed as a preprocessor macro with (), an error +// will be thrown if the proper header defining the internal flag value has +// not been included. +#define BUILDFLAG(flag) (BUILDFLAG_CAT(BUILDFLAG_INTERNAL_, flag)()) + +#endif // BUILD_BUILDFLAG_H_ |