1// Copyright 2015 The Chromium Authors. All rights reserved. 2// Use of this source code is governed by a BSD-style license that can be 3// found in the LICENSE file. 4 5#ifndef BUILD_BUILDFLAG_H_ 6#define BUILD_BUILDFLAG_H_ 7 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. 13// 14// This is for use with generated headers. See build/buildflag_header.gni. 15 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) 21 22// Accessor for build flags. 23// 24// To test for a value, if the build file specifies: 25// 26// ENABLE_FOO=true 27// 28// Then you would check at build-time in source code with: 29// 30// #include "foo_flags.h" // The header the build file specified. 31// 32// #if BUILDFLAG(ENABLE_FOO) 33// ... 34// #endif 35// 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: 39// 40// const char kSpamServerName[] = BUILDFLAG(SPAM_SERVER_NAME); 41// 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 44// not been included. 45#define BUILDFLAG(flag) (BUILDFLAG_CAT(BUILDFLAG_INTERNAL_, flag)()) 46 47#endif // BUILD_BUILDFLAG_H_ 48