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
