Ifdef macro. dave_59 September 10, 2011, 4:43am 2.

Ifdef macro #define CALC_MODE right before this. Why ifndef is not allowed inside a macro? 1. But a little difference is there. :. @MarcW Also, -U works not only with macros defined on the command line, but on predefined macros. Any inner conditional preprocessing blocks are processed separately. If you are running gcc you can do gcc -E myfile. C言語における#defineマクロは、定数やコードの置き換えに使用されます。 一方、#ifdefは条件付きコンパイルを行うためのプリプロセッサディレクティブです。 これにより、特定のマクロが定義されているかどうかをチェックし、その結果に応じてコードの一部をコンパイルするかどう #ifdef MACRO or #if defined (MACRO) checks whether the macro is defined, with or without value. Same for all TARGET_* macros. #else語法： #ifdef MACRO //successful code #else //else code #endif. 下面來看看一個簡單的例子來了解如何使用#ifdef預處理器指令。創建一個源文件：ifdef-example. Therefore there are `ifdef, `ifndef, and `elsif. Furthermore, yes: ifdef, undef, etc are processed at pre-processing time -- the compiler never even sees these so-called directives. If the log level is set to exclude, say, debug statements, then logging. Blogs. If the There's no need to use a macro(), just do: #ifdef I int i0; #end #ifdef U int u2; #endif Be aware that use of macro's and conditional compilation obscures things; so only use this when really necessary. It will expand to given value in the Using directives like ifdef, ifndef, and endif, you can conditionally compile sections of code based on whether certain macros are defined. Because of this, many C/C++ compilers define their own methods for doing pragma-like things, and they often can be embedded in macros, but C #ifdef with programming examples for beginners and professionals covering concepts, control statements, c strings and more. Macro by using #ifdef doesn't work. anaging conditional compilation in your Verilog code. So it doesn't matter what you pass. 5. As others have pointed out, if the header file containing the macro definitions is structured so that it does not contain any typedef or enum declarations (these cannot be repeated; function and variable declarations can be repeated), then you could #undef the macro, do what you need without the macro in effect, and then re-include the header, possibly after undefining #ifdef MACRO Not valid C or C++ code */ - does no harm #endif - oops more invalid code #endif and comments: /* Not valid C or C++ code #endif - does no harm */ - oops */ Comments are for commenting, #ifdef are for disabling legal code. The macro is provided in the header <cstdint>. #ifndef not working as expected. Evaluate macro depending if another macro is defined. h" Update: @Vlad worked out the full solution in the meantime - kudos to him (and +1 :-) No, there is no portable way of doing that. 2. It's equivalent to #if Sometimes you wish to use some code if a macro is not defined. With the IFDEF macro, during compilation it is able to detect if a Genie substitution is valid or not. In some contexts this shortcut is You can use this macro for temporary hacks, for example to get around code that a co-worker hasn't written yet, to make sure you don't forget to fix it once you want to release a build to the public. conditional: if-part elif-parts opt else-part opt endif-line if-part: Unlike C and C++ directives, you can't use these directives to create macros. You're supposed to use #if BOOST_COMP_GNUC and not #ifdef since the macro is always defined (but may be zero). defined name and defined (name) are both expressions whose value is 1 if name is defined as a macro at the current point in the program, and 0 otherwise. Deepak Reddy Deepak Reddy. The defined preprocessing operator yields true if the identifier names a defined macro (i. Syntax: Those conditions above are for general material, mostly macros and short text. Build your code with gcc -c foo. So if you define UNICODE, then GetWindowText will map to GetWindowTextW instead of GetWindowTextA, for example. For more details of the context stack, see Section 4. #ifndef conditional #if defined(MACRO) is the same as #ifdef MACRO, but is longer. Reviews. - Evaluate the following lines only if Macro is not defined. -else. C++ `ifdef` with concatenation of macros values. AJM. See related question and answer: Document a config macro with doxygen Basically: In the doxygen configuration file, add: PREDEFINED = IN_DOXYGEN Somewhere in the source code, add: /* Exporting build configuration macros to doxygen, so they get documented. Note that, in your C source file, WITH_ATS is just an empty macro (i. Hot Network Questions Coq: unfold a class nested in the goal The first option is perhaps a bit closer to a C-style #ifdef macro than using Loader, as it works at the file level. Programs. You can nest conditional How can I pass a macro to the preprocessor? For example, if I want to compile some part of my code because a user wants to compile unit test, I would do this: #ifdef _COMPILE_UNIT_TESTS_ BLA B Apparently __ANDROID__ is a specific GCC macro that it supposed to define internally whenever correct options are provided. Grammar. How do you disable dead code warnings at the crate level in Rust? 256. Intel's compiler also defines _MSC_VER and _MSC_FULL_VER This SO answer on - Is #if defined MACRO equivalent to #ifdef MACRO? explains it wonderfully. Viewed 4k times 4 . How can I do this? The #ifdef/#ifndef conditional only cares about the macro identifier, so the arguments are not part of its syntax. You cannot do precisely what you want because #ifdef operates on an identifier, not a preprocessor expression, and the ## operator can only be used in the replacement text of a macro definition. #endif environment. Then again, there are no portable ways to use #pragma at all. Can i use ifdef in a macro defination , ex-define xyz \ assign x = 1;\ ifdef SAMPLE_SWITCH \ assign z = 0;\ else assign z= 1; `endif \ Thanks Vikram dadwal. For example, you could define a DEBUG_PRINT macro that expands to a printf call for debug builds but expands to nothing for non-debug builds. Explanation. The macro is set to 201703L if the /std:c++17 compiler option is specified. I have my own debug macro called TWDEBUG that I use in a static library I create for sharing. c++ - #ifdef macro. When you undef PROC_ADD inside the ifdef'd code, the preprocessor has already decided which section of code to include and which to ignore. #ifdef allows a section of a program to be compiled only if the macro that is specified as the parameter has been defined, no matter which its value is. First, note that using the XOR-operator for swapping, although a commonly taught trick to avoid using a temporary, fails if the two arguments are the same object. By using these directives, you can create more flexible and configurable designs, improve code readability, and manage different design FWIW I used exactly this technique long ago while working with another interpreted language, PostScript, and found it very useful -- mainly for #include'ing files and #ifdef'ing statements, not so much for macro substitution. It's sometimes easier to ensure that all lines of a macro end with ` than to ensure all but the last line does so. 3 Defined . _TEXT vs. , it doesn't have any value associated), whereas in your makefile, WITH_ATS is a variable that takes the value passed at the command line, e. Aarbitrary text should not reside in the source at all. Comparing strings. The stringify macro S() uses macro indirection so the value of the named macro gets converted into a string. You have to "use" the result, somehow. @RemyLebeau Yes, we can use #ifdef with #elif. It then evaluates the expression that it find. 4. However, #ifdef cannot be used in a macro. 4) (Linux). Free Courses. #define macro for debug printing in C? 546. If string-2 is omitted, it is taken to be the empty string (according to the normal rules). controlled text will be included in the output of the preprocessor if and only if MACRO is defined. Typically you would include a central header file defining the selected OS symbol and use OS-specific include and library directories to compile and build. If the identifier specified is defined as a macro, the lines of code that immediately follow the condition are passed on to the compiler. While they serve a similar purpose, there is a slight difference between them. 6k 22 22 If you just want to disable logging methods, use the logging module. Ask Question Asked 15 years, 7 months ago. Share Where #ifdef expect a macro rather than macro expresssion. Hot Network Questions Volume of frozen condensation in a ceiling feasible? C++ `ifdef` with concatenation of macros values. Thus, #if defined MACRO is precisely equivalent to #ifdef MACRO. sv” elsif VALUE equals 2 include “testcase_2. This directive controls whether nullable annotations have effect, and whether #ifdef MYDLL_EXPORTS /*Enabled as "export" while compiling the dll project*/ #define DLLEXPORT __declspec(dllexport) #else /*Enabled as "import" in the Client side for using already created dll file*/ #define Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand; OverflowAI GenAI features for Teams; OverflowAPI Train & fine-tune LLMs; Labs The future of collective knowledge sharing; About the company ifdef(`foo', "foo' is defined', "foo' is not defined') =>foo is not defined define(`foo', `') => ifdef(`foo', "foo' is defined', "foo' is not defined') =>foo is defined The macro ifdef is recognized only with parameters. If the macro is defined, the code block following the #ifdef directive is included in the compilation. More. , 0 for make WITH_ATS=0. On the other hand it allows to add extra conditions with || or && . 10. If I import the static library to my new project and use it, the compiler does not seem to recognize it. dave_59 September 10, 2011, 4:43am 2. Follow edited Mar 29, 2023 at 0:38. You must use the #endif directive to end the conditional compilation directive. " A compiler in C mode defining it anyways is broken, so this particular example isn't a very strong argument for #if over #ifndef . 8. The value doesn't matter. Let's see a simple example to use #ifdef preprocessor directive. #ifdef / #ifndef: Conditional compilation based on whether a macro is defined or not. Thanks for your help! 0 votes Report a concern how to use #ifdef inside a macro?'#' is not followed by a macro parameter. Start Learning Undefines a macro. 2. It is a relatively recent The macro does not work in GNU gcc (tested at version 4. 14. The code below work as expected. godbolt. Modified 15 years, 1 month ago. For each standard attribute, it is implementation-defined whether __has_cpp_attribute expands to the value given in the table below (which is the year and month in which the attribute was added to the working draft) or 0 . #ifdef示例. The preprocessor can test whether a symbol is defined or not (using #ifdef and the defined operator), and it can evaluate constant integer expressions (using #if). As with %ifdef, the inverse and %elif forms %ifnctx, %elifctx and %elifnctx are also supported. Question is, I have logs under #ifdef DEBUG which I want to print only for debug build. I want to run some c++ code on Linux and Windows. predef is outdated, mentions old Intel compiler:. check macro OR true condition in #ifdef. For a sample use of %ifctx, The n1570 C draft standard, section 6. For example, #define PI 3. Leave CONDITION and the directive named macros without a definition. Conditional inclusions (#ifdef, #ifndef, #if, #endif, #else and #elif) These directives allow to include or discard part of the code of a program if a certain condition is met. it has pretty straight-forward logic, but may confuse due to definitions being allowed both inside and outside of any functions. Their values are the major version, minor version, and patch level of the compiler, as integer constants. Viewed 4k times 2 I am new to C, and I am maintaining someones code. Horizon_Net. h if WITH_ATS is defined. The controlled text inside of a conditional can include preprocessing directives. It can be used as a way to introduce a long comment Is there a way to do ifdef like checks in assembler to do one thing if I'm on Windows and another under Linux and also handle 32 vs 64 bit that way? Related: NASM/YASM doesn't predefine many macros to let you detect platforms easily with %ifdef / %endif. answered Nov 28, 2016 at 15:47. debug will be very close to a no-op (it just checks the log level and returns without interpolating the log string). I can perform various checks/operations on object-like macros: #ifdef _SOME_OBJECT_LIKE_MACRO // check if some object-like macro is defined #undef _SOME_OBJECT_LIKE_MACRO // undefine some object-like macro #endif #define _SOME_OBJECT_LIKE_MACRO 0xff 6. wrapperToA. 8 (Predefined macro names), clause 3 states "The implementation shall not predefine the macro __cplusplus, nor shall it define it in any standard header. i. Also, take a look at libnuwen's compiler. config command example: gpio_config a 5 opp nopull flow none\r write command example: gpio_write a 5 1\r parsing the command is done in another part of my program, my application is a shell implemented on a MCU (STM32Fxx for the moment, so my code should Take a look at the Pre-defined C/C++ Compiler Macros project on Sourceforge. The macro ifelse can take more than four arguments. If string-1 and string-2 are equal, ifelse expands into equal-1, otherwise the procedure is repeated with the first three arguments Preprocessors in C are programs that process source code before compilation, involving steps like macro definition, file inclusion, and conditional compilation, with directives such as #define, #include, and #ifdef guiding the preprocessing actions. It is 0xFFFFFFFF on a 32-bit platform, and 0xFFFFFFFFFFFFFFFF on a 64-bit platform. To allow for this to be called multiple times either inside a function or at Raymond Chen explains it here: TEXT vs. Each of #if, #ifdef, #ifndef, C++ Macros #ifdef. - Only allowed after the ifdef, ifndef, if, and elif directives. . The question was originally tagged with C, and the title included 'C' rather than C++. Doing it as a paramterised macro is a bit odd. By defining a macro named CHECK_DEBUG we can change the result if the macro was not defined, e. Thus USER##_VS becomes jack_VS (or queen_VS), depending on how you set USER. How can I use "else if" with the preprocessor #ifdef? Hot Network Questions Which door leads out? Reducing 6V to 3V How to change file names that have a space in the name The keyword `ifdef simply tells the compiler to include the piece of code until the next `else or `endif if the given macro called FLAG is defined using a `define directive. – The same still applies, you can use #ifdef #endif to get conditional compilation depending on whether the macro in question exists or not. #endif. There are some pieces of platform-specific code, which I should place in #ifdef . This is very useful. Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand; OverflowAI GenAI features for Teams; OverflowAPI Train & fine-tune LLMs; Labs The future of collective knowledge sharing; About the company Visit the blog #ifdef checks whether a macro by that name has been defined, #if evaluates the expression and checks for a true value. String comparison in preprocessor conditions in C. h. The # directives are compile time and not run time. How do I use the character "#" successfully inside a Macro? It screams when I do something like that: #define DO(WHAT) \ #ifdef DEBUG \ MyObj->WHAT() \ #endif \ You can use the #ifdef and #ifndef directives anywhere #if can be used. #ifdef and #if defined are both preprocessor directives in the C programming languages that are used for conditional compilation. These macros are defined by all GNU compilers that use the C preprocessor: C, C++, Objective-C and Fortran. For example, here I to list clang’s pre-defined macros: clang -x c /dev/null -dM -E; to list gcc’s pre-defined macros: gcc -x c /dev/null -dM -E (not that on mac gcc is actually clang that ships with XCode) the -x c /dev/null -dM -E also works for mingw (which is based on gcc) listing predefined macros for other compilers (C99, 6. We say that the conditional succeeds if MACRO is defined, fails if it is not. instead of the name of the macro. If yes, it executes the code otherwise #else code is executed, if present. single-line #ifdef in C/C++. For example, with: #ifdef XYZZY int a; #ifdef PLUGH int b; #endif int c; #endif The b variable will exist only if both XYZZY and PLUGH are defined. Yes you can. If you are willing to define ENABLE_MODULE_1 (if defined at all) with a non-zero constant as its replacement text, you can achieve something similar to what you want as Another thing I'd suggest doing is to place ` after all useful lines of the macro, and add a comment afterward saying something like // Blank line required after macro. h" #endif That is, to include ats. Either How to write a macro function that uses #ifdef. At the ((void)sizeof( it errors with expected identifier or '(' before 'void' and expected ')' before 'sizeof'. in(in1), . 3. #define TEST CAT(CHECK_,DEBUG), 0, 1 #define CHECK_DEBUG ~,~ If DEBUG is not defined the result will be ~, ~, 0, 1 (4 comma-separated tokens); If DEBUG is defined the result will be CHECK_, 0, 1 (3 comma-separated tokens); 4. Since defined() will evaluate to a 0 or 1, it'll behave as a normal #if 4. On windows, I must support visual studio and mingw. #elif WINDOWS_KEY_WORD // windows code goes here. Conditional Compilation #ifdef. However, since control over options is largely delegated to NDK, one should not rely on __ANDROID__ macro being ever defined. I use Eclipse IDE for C++ coding on Linux. The syntax for the #ifdef directive in the C language is: #ifdef macro_definition macro_definition The macro definition that must be defined for the preprocessor to include the C source code into the compiled Small correction: #ifdef TARGET_OS_MAC will get you always true on both OS X and iOS, as it is defines either 0 or 1 depending on platform, but when APPLE is defined, TARGET_OS_MAC is defined as well, so checking it inside the #ifdef APPLE is worthless. I rely on NDEBUG, because it's the only one whose behavior is standardized across compilers and implementations (see documentation for the standard assert macro). See this Q&A for some platform-detection tricks. 7. macros to prevent redefinition errors. sv” Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand; OverflowAI GenAI features for Teams; OverflowAPI Train & fine-tune LLMs; Labs The future of collective knowledge sharing; About the company C言語のプリプロセッサディレクティブである#ifdefは、特定のマクロが定義されているかどうかをチェックするために使用されます。 このディレクティブは、条件付きコンパイルを実現するために役立ちます。 例えば、デバッグ用のコードを含めるかどうかを制御する際に#ifdef DEBUGを使用する That's why undef is important; many headers define a lot of short macros like MIN and MAX or N that are desirable macro names; almost none use lowercase macros under 3 characters in length so foo/bar/baz/a/b/c should be really safe short duration scope macros. Follow edited May 28, 2014 at 13:58. In many cases, however, this shortage of functionality could be augmented by using generate verilog void print_os() { #ifdef _WIN32 std::cout << "You're on Windows!\n"; #elif __linux__ std::cout << "You're on a Linux OS!\n"; #elif __APPLE__ std::cout << "You're on Mac OS!\n"; } Both ways do not generate code for the other platforms when compiled, so they are technically the same, and as such, I would prefer the constexpr way (if it were If you use C++11 then you can check the value of the macro SIZE_MAX which is the maximal value that a std::size_t type variable can hold. There are two different builtin conditionals in m4. defined name and defined ( name ) are both expressions whose value #ifdef CALC_MODE typedef MyCalcClass ChosenClass; #elifdef USER_MODE typedef MyUserClass ChosenClass; #else static_assert(false, "Define CALC_MODE or USER_MODE"); #endif So I can do. Usage of #ifdef in between if else condition. You can do this by writing ‘ #ifndef ’ instead of ‘ #ifdef ’. Thanks for your help! What is #ifdef? #ifdef stands for “if defined. Hot Network Questions How do I get the drain plug out of the sink? How can a communist government reduce the size of government? How would you recode this LaTeX example, to code it in the most primitive TeX-Code? Is it possible to make a flight simulator that can model aerobatics and stalls #ifdef DEBUG //some logging here #endif The question is: what compiler definition is available on all platforms in the CMake "Debug" build type? FWIW, the proper way to add macro definitions (now, at least) is add_definitions(-DMY_DEBUG). 3 Defined ¶. If given more than four arguments, ifelse works like a case or switch statement in traditional programming languages. The preprocessor determines if the provided macro exists before including the subsequent code in the compilation process. To rely on something like _DEBUG would be to rely on an implementation detail of a particular compiler The conditional-assembly construct %ifctx ctxname will cause the subsequent code to be assembled if and only if the top context on the preprocessor’s context stack has the name ctxname. user4268862 user4268862. To fix this, I'm putting a -U for this symbol, You could include the problematic header files always via your own dedicated header files, where you can add the necessary #ifdef, #undef etc. I came across this in the header file. Macros can span multiple lines using a backslash (\) at the end of each line except the last. They work in a verbatim way. I can resign the use of static_assert if needed. How to use #ifndef with macro argument? 0. Use C preprocessor macros like __BIG_ENDIAN__ and __LITTLE_ENDIAN__ to test endianness at compile time. Topics. It's is more powerful, as you can include <<-separated values in the argument, so with a single argument you get something that would require a variable number of macro arguments in C. But when I change #ifdef to #ifndef and remove #define macro, the code get executed. ” It checks whether a macro (symbol) has been defined earlier in the code using #define. Kind of a corollary answer: the people on this site have taken the time to make tables of macros defined for every OS/compiler pair. , a macro that has been defined with #define and not yet undefined via #undef) and false otherwise. As long as you don't overuse Loader, though (e. If you want to actually remove chunks of code at bytecode compile time conditional on a particular variable, your only Use #define OSsymbol and #ifdef OSsymbol where OSsymbol is a #define'able symbol identifying your target OS. Nullable context. You might want to use #if TARGET_OS_MAC instead. I tried separating these lines out with If-Else statements, but the code won't There are two types of macros - function-like macros and object-like macros. 31. – Blaze Commented Feb 1, 2019 at 9:34 #ifdef MACRO //controlled text #endif /* name_of_macro */ Below is the syntax of #ifdef in the C programming language that has an else part as well. 宏IFDEF(macro, )的第一个参数是一个布尔宏，第二个参数是变长列表，可以传入语句或代码块。若宏macro被定义则保留代码，反之什么都不保留。在它的顶层定义中使用了宏MUXDEF(macro, a, b)，它是一个广义的选择器，不管a和b的类型是什么。 using macros to place #ifdef in the code. if GAS macro stuff. 1. Modified 15 years, 7 months ago. If the macro PKT is defined then "Packet" is printed, else not. C++ Macros #ifdef. This has similar functionality to an ifdef except that you get parentheses to delineate the beginning and end (which most IDEs have no problems code-folding) While you can still use #define and #ifdef within the context, #include is not allowed. e use of Active Compilation Conditions. Getting an if-statement to also check for a defined macro. The conditional preprocessing block starts with #if, #ifdef or #ifndef directive, then optionally includes any number of #elif, #elifdef, or #elifndef (since C23) directives, then optionally includes at most one #else directive and is terminated with #endif directive. Each directive’s condition is checked in order. New setting: So, the macro USER_VS has the expansion jack_VS or queen_VS, depending on how you set USER. #ifdef x is equivalent to #if defined(x). Follow edited May 2, 2024 at 0:40. The tags were predominantly C++ tags, though. Each of #if, #ifdef only cares if MACRO has been defined or not. The #ifdef directive requires a single identifier; 1 is not an identifier. c / . Is it ok to put standalone #undef, if I want to only undefine a macro ? Does that make the coding practice The #ifdef directive checks for the existence of macro definitions. Syntax. #define FOO 1 #define BAR 0 #ifdef FOO #ifdef BAR /* this will be compiled */ #endif #endif #if BAR /* this won't */ #endif #if FOO || BAR /* this will */ #endif The #ifdef directive checks for the existence of macro definitions. c，其代碼如下所示 - #ifdef 1 is ill-formed. Use #ifdef __APPLE_CC__ to wrap any Mac OS X-specific code. Allowing a custom macro in #ifdef check. However, C11 §6. I am facing similar problem. Some of these are standard, and some are compiler-specific extensions. However, there are other compilers that can be used from Visual Studio, and these compilers usually also define _MSC_VER. The #ifdef preprocessor directive checks if macro is defined by #define. The macro is set to 202002L if any #define macros is not local, nor global variable, but a "constant-like" expression, so, even if some DEFINED_VALUE will be #undefined anywhere after - this un-definition will be scoped from its place to the end of this source-file. In this article. What macro is predefined on Mac OS X platform and XCode development environment that should be used to distinguish OSX-specific code in C/C++ programs? #ifdef __GNUC__ #ifdef __MINGW32__ For additional macros you might be interested in this page which shows other compiler macros. – Peter Cordes. 1,743 3 3 gold badges 17 17 silver badges 31 31 bronze badges. The negative logic is a small readability speedbump, but it's a common idiom you can quickly adapt to. Hot Network Questions Encoded message signed using pycryptodome differs from the one signed using BouncyCastle Is sales tax determined by the state in which the SELLER is located, or the state in which the PURCHASER is located? 5 Jan 2021: link update thanks to @Sadap's comment. Then you can use comment, xcomment, tagging packages for longer text (but not for macros). You might use #ifndef MACRO / #define MACRO 1 / #endif so that the programmer can override the default setting on the compiler command line with -DMACRO=0, without needing to edit the source code. -ifndef(Macro). Some of the common uses of C preprocessors are: The usual way to test whether a preprocessor symbol is defined is using #ifdef. Does ChiselHDL also support something like this for debugging? Or, any other alternatives? in scala contexts, @elidable(WARNING What is the most reliable way to find out CPU architecture when compiling C or C++ code? As far as I can tell, different compilers have their own set of non-standard preprocessor definitions (_M_X86 in MSVS, __i386__, __arm__ in GCC, etc). Confusion with Preprocessor Directives. For an example of a way to make defining blind macros easier, see Composition. The body, controlled text, will be included in compilation if and only if MACRO is defined. If the substitution is not valid you are able to hide it from the page, thus making your Genies more generic and reusable in more contexts. Improve this answer. 1 Testing if a macro is defined. These transformations can be the inclusion of header files, macro expansions, etc. I tried to use something like this: #ifdef _DEBUG cout << "Debug!" << endl; #endif But it doesn't work when I select Debug in IDE. If the expression you write (after the #if) has a nonzero value, the line group immediately following the #if directive is kept in the translation unit. Follow edited Nov 28, 2016 at 15:55. Is there a standard way to detect the architecture I'm building for? If not, is there a source for a comprehensive list #define MY_MACRO #ifdef MY_MACRO int foo = 0;//proper indent, normal color #else int bar = 0;//proper indent, and gray color #endif Share. 1p4) "After all replacements due to macro expansion and the defined unary operator have been performed, all remaining identifiers (including those lexically identical to keywords) are replaced with the pp-number 0"" The original C preprocessors required explicit #ifdef validation before using a symbol. The #ifdef will compile all code if a given macro is defined. out(out2)); `else endmodule and generate: Allowing a custom macro in #ifdef check. Use #ifdef __GNUC__ to wrap any GCC-specific code. #ifdef MACRO // code #else //code of else. I did set up preprocessor macros to TWDEBUG and Other C flags and Other C++ flags to -TWDEBUG, but when I ran the code the ifdef macro doesn't get This block is called a conditional group. Otherwise, if we #define macro with value 0 for #elif case, the #elif case test it to false. Commented Jul 15 #ifdef NOOP static inline void conditional_noop(int x) { } #else static inline void conditional_noop(int x) { std::cout << x; } #endif Using inline function void enables type checking, even when NOOP isn't defined. S files exactly as you would in . thanks@Lud, this is a solution to tell whether the MACRO is defined, but not what i want #ifdef #else #endif macro question. You should test #ifdef macro before defining, and if it is, undef it if it's in use. Why use apparently meaningless do-while and if-else statements in macros? 263. Can `#ifdef` be used inside a macro? Hot Network Questions What sense does it make to use a Vault? Is "Klassenarbeitsangst" a real word? Does it accord with general rules of compound noun formation? Only code compiled as C++ sets it. Is there a standard #ifdef that once can use? Something like: #ifdef LINUX_KEY_WORD // linux code goes here. Firstly, there are macros that are implicitly defined by the compiler (for example, __cplusplus). 6. While this seems appealing as a quick way of @Lundin , yes i send commands via a serial link (UART in in my case) to configure ports, read pins etc. Pre-processor conditionals will nest. 1 Conditional inclusion /6:. 15. All accept only a single argument which is the name of a text macro. For example: Identifiers that are not macros, which are all considered to be the number zero. E. Follow That will not work for a generic macro-test macro such as you propose, however, and it also is limited by the fact that it determines whether the condition holds at the point where the macro is defined, not the point where it is used. Also, changing MACRO to 2 would not change things — setting it to 0 would. For example, you can see that _WIN32 is NOT defined on Windows with Cygwin (POSIX), while it IS defined for compilation on Windows, Cygwin (non-POSIX), and Use C preprocessor syntax in . The first is ifdef: Builtin: ifdef (name, string-1, [string-2]) If name is defined as a macro, ifdef expands to string-1, otherwise to string-2. DEFINE CONDITION to control which value NESTED gets on compilation, similarly to normal #ifdef usage: DEFINE CONDITION NESTED int i = REPLACED; //i == 1 UNDEF CONDITION NESTED int z = REPLACED; //z == 0 Source code that uses NESTED and the other macros will not compile. The ifdef directive lets you include or exclude blocks of code based on whether a specific macro is defined, while elsif allows for multiple conditional checks within your code. I have a question about preprocessor directives in C++: For example: #ifndef QUESTION // Some code here #ifndef QUESTION // Some code here #endif #endif Can we use it in this way, and can the C言語におけるプリプロセッサディレクティブの#ifdefと#if、#defineは、条件付きコンパイルに使用されます。 #ifdefは、指定されたマクロが定義されているかどうかをチェックします。定義されていれば、その後のコードをコンパイルします。 一方、#ifは、式が真であるかどうかを評価 The Microsoft compiler will define the _OPENMP macro when the /openmp compiler option is set. Share. The special operator defined is used in ‘#if’ and ‘#elif’ expressions to test whether a certain name is defined as a macro. Overloading Macro on Number of Arguments. This allows you to write #if MACRO instead of #ifdef MACRO, if you know that MACRO, when defined, will always have a nonzero value. #if MACRO is similar to #ifdef MACRO but not I decided to write a function to modify those strings, delete the "#ifdef" "#else" & "#endif" as well as the stuff between them based on the macro. Alternatively, you could convert your macro to a function-like macro and avoid using #if. The other conditional, ifelse, is much more powerful. But in principle size_t x = (sizeof( instead does work as intended. If I understand this correctly, cocos2d-x is one of several possible APIs. For your purpose you can use it in this form: #ifdef _OPENMP #include <omp. I have code that needs to run on both Excel 2003 and Excel 2007, and there are a few spots where changes in the versions cause the code to halt. Instead of using an #ifdef within a macro (which isn't permitted), it helps you include a file multiple times, with different macros defined each time, so that the file can use #ifdef. However it worked on Windows. as a delegate in a large view), they should both do the job fine. That is the correct behaviour. The C preprocessor is a macro preprocessor (allows you to define macros) that transforms your program before it is compiled. – Compare the following use of IFDEF: module module1 ( input in1, output logic out1 `ifdef COND , output logic out2 `endif ); assign out1 = in1; `ifdef COND submodule submodule1(. Ask Question Asked 15 years, 1 month ago. The definition of the macro has to be defined for the preprocessor for including the source code of C into the application which is compiled. Preprocessor directives in C++. hh header for a decent way to 'normalize' compiler versioning macros. #ifdef MACRO //code #endif. The #ifdef identifier statement is equivalent to #if 1 when identifier has been defined. 5,979 4 4 gold badges 32 32 silver badges 34 34 bronze badges. On the other hand, there is a slim chance that people will abuse it by including a semicolon in the argument. Similarly, the TEXT macro will map to L"" instead of Verilog does not provide such a facility. #ifdef MACRO controlled text #endif /* MACRO */ This block is called a conditional group. Some things to consider: Don't use a macro name starting with an underscore; such identifiers are reserved to the implementation. In the C Programming Language, the #ifdef directive allows for conditional compilation. 21. If the macro is defined, the code block following the #ifdef The special operator defined is used in ‘#if’ and ‘#elif’ expressions to test whether a certain name is defined as a macro. Checks for the support of an attribute named by attribute-token (after macro expansion). g. answered May 28, 2014 at 13:28. Learn everything about macros in C, including types such as object-like, function-like, and predefined macros. Macro generation depending on preprocessor conditionals. New build settings. Refer to Building and Linking in Xcode 8 Release note. defining #ifdef at runtime. The #if directive, with the #elif, #else, and #endif directives, controls compilation of portions of a source file. _T, and UNICODE vs. */ #ifdef IN_DOXYGEN # define EXCLUSIVE_MACRO_ONE # define EXCLUSIVE_MACRO_TWO # In many of the C and C++ files I have seen macros like this: #ifdef X #undef X // no statements in between #endif I feel that, it's adequate to simply write: #undef X If the macro X wasn't defined, then the #undef should have no effect. There are some pieces of code that I want to include only for one operating system and not the other. The #ifdef directive checks if a macro or identifier is defined, and if it is, the code within the #ifdef block is compiled. #if MACRO substitutes the macro definition; if the macro is not defined then it substitutes 0. The a and c variables depend only on XYZZY. I can understand that if the source is compiled on the windows it will enter the if statement else if the code is compiled on a I have a problem with _DEBUG macro on Linux C++. The documentation suggests that it recognizes -or / as prefixes, so it should be OS agnostic The following macro directives support conditional compilation:-ifdef(Macro). Thus CPP stuff happens entirely before and separately from any . Again, no mention about __OSX__ macro. h>. This of course The Boost Preprocessor (which works for C as well as C++, even though Boost as a whole is a C++ library) library can help with this kind of task. From the C11 standard, section 6. 8 Predefined macro names ¶3 says: The implementation shall not predefine the macro __cplusplus, nor shall it define it in any standard header. #if checks for the value of MACRO and evaluates MACRO accordingly. The compiler behind NDK might not be GCC for all we know (or care). What I need is a way to check in a macro if an argument of that macro is a defined preprocessor symbol. Based on macro value I have to compile different testcases As follows ##### ifdef VALUE equals 1 include “testcase_1. Any file that neglects to include the header defining the macro then would fail to compile. – rosshjb I decided to write a function to modify those strings, delete the "#ifdef" "#else" & "#endif" as well as the stuff between them based on the macro. void func { // some code here #ifdef DEBUG print_log() // this portion should execute only for debug builds #endif // some code here } Is there a macro I can use for checking the current configuration type in visual studio? Depending on the current setting I'd like to either include a main or dllmain function: #IFDEF CONFIGURATION_TYPE_EXE int main(int argc, char **argv) { I've googled that Scala uses "@elidable" as a kind of macro in C++. - Evaluate the following lines only if Macro is defined. Your dummy function would generate compilation warnings about unused arguments #if defined(_MSC_VER) && !defined(__clang__) // code for msvc compiler #endif _MSC_VER is used to test MS Visual C/C++ compilers. Why not just do something like this: #ifdef USE_CONST #define MYCONST const #else #define MYCONST #endif Then you can write code like this: MYCONST int x = 1; MYCONST char* foo = "bar"; IFDEF equivalent in VBA. I'm writing a cross-platform code, which should compile at linux, windows, Mac OS. Peter Mortensen. However, your macro has a couple of weaknesses that should be addressed. The macro is the integer literal value 201402L by default, or when the /std:c++14 compiler option is specified. What is #ifdef? #ifdef stands for “if defined. #ifdef WITH_ATS #include "ats. PGI's compiler has a __PGI macro. They are executed only if the conditional succeeds. If we take the five examples above, #if MACRO will be turned into. h ----- #ifdef VAR #undef VAR #endif #include "a. ifdef and other GAS macro functionality isn't designed to replace CPP. One approach would be to define a numeric code for each API: A major change of ifdef replacement came up with Xcode 8. I have my doubts about putting both sets of Is the second code snippet analogous to the one in C? More or less. 8. The macro ifdef is recognized only with parameters. Syntax: #ifdef MACRO_NAME Where MACRO_NAME is our macro to test if defined. Something like this . However, they are not robust sometimes: you can't use unbalanced \else, \fi, \ifXXX in the branches, for very long text it may cause surprising errors. Function-like macros used without their function call parentheses are also treated as zero. The #nullable preprocessor directive sets the nullable annotation context and nullable warning context. But note that I'm new to cmake, so up front, my apologies this question is too basic . c and check the result after preprocessing. The special operator defined is used in `#if' and `#elif' expressions to test whether a certain name is defined as a macro. The C99 standard says essentially the same, in a slightly different The ifdef condition is evaluated when the preprocessor gets to it. I'm dealing with a case compiling code on Termux where the builtin definition of __ANDROID_API__ as 24 is failing to reveal functions that are in fact declared in headers and available for linkage. 0. All preprocessing directives begin with a # symbol. Instead of using #ifdef , use #if defined() . _UNICODE: The plain versions without the underscore affect the character set the Windows header files treat as default. Is it possible to compare #ifdef values for conditional use. The conditional preprocessing block starts with #if, #ifdef or #ifndef directive, then optionally includes any number of #elif, #elifdef, or #elifndef (since C++23) directives, then optionally includes at most one #else directive and is terminated with #endif directive. One common use of ‘ #ifndef ’ is to include code only the first time This C tutorial explains how to use the #ifdef preprocessor directive in the C language. h> // This line won't add the library if you don't compile with -fopenmp option. There is only one action possible with text macros: checking for their existence. But, If we #define macro with value 0 for #ifdef case, the #ifdef case tests it to true. More subtly, #ifndef HEADERFILE_H can violate the implementation's namespace of the header name happens to start with E; identifiers starting with E and a digit or uppercase letter are reserved to <errno. A preprocessor directive must be the only instruction on a line. If you remove the bunch of preprocessor directives from your getval function, then the "Packet" will not be printed, Genies are customizable, reusable objects that are even more flexible when used with the IFDEF macro. e. Use functions like htonl, htons, Older code sometimes used conditional statements like #ifdef __MACH__ or #ifdef __APPLE__ to try to determine whether it was being compiled on OS X or not. Combining C++ and C - how does #ifdef __cplusplus work? 954. #define FEATURE_A 1 void function() { // some code #ifdef FEATURE_A // code to be executed when this feature is defined #endif // some code } The program does not execute code inside #ifdef - #endif. S (not as directly), which causes gcc (the compiler front-end) to run your file through CPP before feeding it to as. xsntz bbqsfo inouv otow jymuvud nmoj shn qdfkmud bti tvtmkbz