Making statements based on opinion; back them up with references or personal experience. One of C's preprocessor operators is the # which surrounds the token that follows it in the replacement text with double quotes ("). Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. In Cereal there are 3 valid Archive types: JSON, XML, and Binary, and I wanted the user to be able to input those as a string variable within CMake. So it is more of a stylistic thing to be able to compare against a "string" like thing in your code. The C Preprocessor is not a part of the compiler, but is a separate step in the compilation process. The preprocessor fit for such extensions to those used in the replacement list of identifiers: each parameter from this list, which is not a string (#) sign (#@) or symbol operator (##) is preceded and no symbol operator followed by the replaced macro call variable names used. How can the C++ Preprocessor be used on strings? I tried this out on GCC 4.9.1, & I don't believe this will do what you think it does. How do I make the first letter of a string uppercase in JavaScript? This does not work. Preprocessor directives are not statements, so they do not end with a semicolon (;). The following sample generates CS1032: // CS1032.cs namespace x { public class clx { #define a // CS1032, put before namespace public static void Main() { } } } Is this an at-all realistic configuration for a DHC-2 Beaver? See comment by @Artyer.]. Only the last character of the "strings" are compared. Is it correct to say "The glue on the back of the sticker is dying down so I can not stick the sticker to the wall"? Storing the code in foo.c and invoking the preprocessor gcc -nostdinc -E foo.c yields: The output is as expected. Does integrating PDOS give total charge of a system? did anything serious ever run on the speccy? This article describes the formal grammar of the C and C++ preprocessor. Here is an example of a macro definition that uses stringizing: The argument for EXP is substituted once, as-is, into the identifier : It is an identifier used in program which will be replaced by value. Why do American universities have so many gen-eds? Why would Henry want to close the breach? Behaviour of the #define directive is the same in both C and C++. So, YMMV on this (or any) answer involving constexpr, depending on the compiler writer's interpretation of the spec. The key is the ## operator. Next: Concatenation, Previous: Macro Arguments, Up: Macros [Contents][Index]. did anything serious ever run on the speccy? By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. One more helpful trick is to #define your xUSER_ macros starting from 1. Making statements based on opinion; back them up with references or personal experience. ANSI token pasting is sometimes less than obvious. Thanks for contributing an answer to Stack Overflow! The last line shows that the USER_VS macro is not expanded before stringization. Thus, stringizing p = "foo\n";results in CGAC2022 Day 10: Help Santa sort presents! In the Preprocessor Definitions dialog box, add, modify, or delete one or more definitions, one per line. The stringify macro S() uses macro indirection so the value of the named macro gets converted into a string. -- Effect of coal and natural gas burning on particulate matter pollution. A: The preprocessor will replace all macros with their definitions, and expand all #include directives by inserting the contents of the included files. or character constants are not duplicated: \n by itself A C macro is just a preprocessor command that is defined using the #define preprocessor directive. That word can makes all the difference in the world. There is no way to convert a macro argument into a character constant. Syntax Explanation #define directives For more information, see Preprocessor and Pragma directives and the __pragma and _Pragma keywords. I would honestly avoid doing this using preprocessor. The preprocessor backslash-escapes the quotes surrounding embedded string constants, and all backslashes within string and character constants, in order to get a valid C string constant with the proper contents. For more information, see Set C++ compiler and build properties in Visual Studio. variadic macro expansion, which allows you to handle macros with variable numbers of arguments. How could I do this with strings and text? so that in my .rc file I can do the following, instead of C ,c,linker,c-preprocessor,header-files,include-guards,C,Linker,C Preprocessor,Header Files,Include Guards,C #define : It is preprocessor directive used for text substitution. Change case of string using PreProcessor CPA Study Group Is it possible to write a C Preprocessor macro which changes the case of a string. The compiler can sometimes tell the results of expressions (even function calls, if they're inline), but not the pre-processor. We do not currently allow content pasted from ChatGPT on Stack Overflow; read our policy here. How does legislative oversight work in Switzerland when there is technically no "opposition" in parliament? ;-D. Putting a single # before a macro causes it to be changed into a string of its value, instead of its bare value. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. The #define directive can use any of the basic data types present in the C standard. Can #if pre-processor directives be nested in C++? How could my characters be tricked into thinking they are on Mars? is it possible to concatenate strings during preprocessing? Not in C98 or C99. WARN_IF to a function would make C programmers want to do; see Description In the C Programming Language, the #define directive allows the definition of macros within your source code. JSON_CHECK_TYPE(<string>) I tried to define concat my macro like: . Asking for help, clarification, or responding to other answers. I cannot make it work on GCC 4.8.1, 4.9.1, 5.3.0. if statement, but not in the string. Preprocessor directives in C programming language are used to define and replace tokens in the text and also used to insert the contents of other files into the source file. Find centralized, trusted content and collaborate around the technologies you use most. This is why you can concatenate strings simply by placing them adjacent to one another: The preprocessing part of the question is simply the usage of the #define preprocessing directive which does the substitution from identifier (H) to string ("Hello "). # define PI 3.14. It is called a preprocessor because it happens before the compilation process. stringize it all together. So TXT_VERPRODUCT would get replaced with six literal strings (including the " " at the end in the six). There are a number of steps involved between writing a program and executing a program in C / C++. Are there conservative socialists in the US? Stringification in C involves more than putting double-quote characters around the fragment. Ready to optimize your JavaScript with Rust? BOOST_PP_CAT(../icons/, BOOST_PP_CAT(num,.ico)). You can't! If you define a compile time helper function for the comparison. Sometimes you may want to convert a macro argument into a string When a macro is expanded, the two tokens on either side of each '##' operator are combined into a single token, which then replaces the '##' and the two original tokens in the macro expansion. Is this an at-all realistic configuration for a DHC-2 Beaver? It contains well written, well thought and well explained computer science and programming articles, quizzes and practice/competitive programming/company interview Questions. Finally to convert the constants JACK or QUEEN to a string, use the stringize (and/or tokenize) operators. Your code compiles correctly, producing a format string of "str: %5s \n". Does a 120cc engine burn 120cc of fuel a minute? If the header file is inside double. The compiler is given a list of directories to search through for included files. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Thanks for contributing an answer to Stack Overflow! did anything serious ever run on the speccy? However, this only seems to work with code. How do I read / convert an InputStream into a String in Java? Unlike normal parameter replacement, the argument is not While this may not solve your particular use case, it does open many possibilities to compare constant strings at compile-time. Just wanted to mention that the same thing goes for regular code as well, not just preprocessors. 10 C#define SQRxx * x[] - C-preprocessor #define SQR(x) ( x * x ) [closed] . Engineering Computer Science C++ part1: Define a class named "Variable" that manages a variable name (string) and a description (string). proper contents. Any constexpr variable equals zero in, This c++11 part of this answer is wrong. 10. C (). Line splicing: Physical source lines that are continued with escaped newline sequences are spliced to form logical lines. The preprocessor backslash-escapes the quotes surrounding embedded string constants, and all backslashes within string and character constants, in order to get a valid C string constant with the proper contents. E.g: As a native speaker why is this usage of I've so awkward? I was browsing the comp.lang.c newsgroup FAQ (ok, somebody needs a life :P), and found this: Question 11.17 I'm trying to use the ANSI ``stringizing'' preprocessing operator `#' to insert the value of a symbolic constant into a message, but it keeps stringizing the macro's name rather than its value. Stringize (#) and token pasting (##) are C preprocessor string manipulation operators. Preprocessor conditionals can test arithmetic expressions, or whether a name is defined as a macro, or both simultaneously using the special defined operator.. A conditional in the C preprocessor resembles in some . C MEX Bug: String Preprocessor Concatenation Not. Each directive occupies one line and has the following format: the # character. Learn more about mex compiler, embedded coder, s-function MATLAB Coder, MATLAB, Simulink. The definition of const-expression used in the #if does not allow strings. Just wanted to make sure he knew strcmp exists, and the response might be enlightening, as I can't think of a reason to do this #define stuff. After the macro is defined, the compiler can substitute the token string for each occurrence of the identifier in the source file. If you were to throw this at the top of your code: then basically, what this does, is that during preprocessing, it will take any call to that macro, such as the following: This allows you a ton of flexibility while coding if you use it correctly, but it doesn't exactly apply how you are trying to use it. '$' is treated as a variable name. As a native speaker why is this usage of I've so awkward? The #define preprocessor directive lets a programmer or a developer define the macros within the source code. The most well-known Macros or Pre-Processor Directives that we used in our program is #define. Advantages of Preprocessor in C. It takes action according to special instructions called Preprocessor directives which begin with #. So, at first the solution sounds pretty simple, just define #define STR (tok) #tok and things will work. And the "VariableString" class that must inherit from the "Variable" class. If somewhere after this `#define' directive there comes a C statement of the form foo = (char *) malloc (BUFFER_SIZE); then the C preprocessor will recognize and expand the macro BUFFER_SIZE. can use the # preprocessing operator instead. However, note that the expected behavior of printf is that it will print the entire string even if the string exceeds the width you specify in the format string. C++ Preprocessor - The Token Pasting (##) Operator This is probably the least understood and most poorly documented preprocessor operator. Connect and share knowledge within a single location that is structured and easy to search. Is this really a constexpr? Debugging preprocessor errors is a pain and I've seen cases where multiple layers of preprocessor replacements and concatenations were used, resulting in disaster when trying to find issues. I don't think there is a way to do variable length string comparisons completely in preprocessor directives. string literals, but it can't actually work with strings. As some didn't like my earlier answer because it avoided the whole compile time string compare aspect of the OP by accomplishing the goal with no need for string compares, here is a more detailed answer. The C compiler will see the same tokens as it would if you had written foo = (char *) malloc (1024); By convention, macro names are written in upper case. C99 added variable argument macros; the upcoming C++0x standard adds variadic macros, as well. We get to use the Haskell type system to introduce a layer of type safety to the C PCRE API. As already stated above, the ISO-C11 preprocessor does not support string comparison. Define preprocessor macro through CMake? One thing that has changed since I first posted this in 2014, is the format of #pragma message. (My apologies in advance as I know this is CMake-centric and that that wasn't part of the original question.). Appealing a verdict due to the lawyers being incompetent and or failing to follow instructions? To subscribe to this RSS feed, copy and paste this URL into your RSS reader. The #define and #undef must be used at the beginning of a program, before any other keywords, such as those used in the namespace declaration.. Did the apostolic or early church fathers acknowledge Papal infallibility? Parameters are not replaced inside string constants, but you It can only be used in a macro definition. Consider a C program that interprets named commands. Stringizing in C involves more than putting double-quote characters around the fragment. So, ultimately, you will have to change the way you accomlish your goal of choosing final string values for USER and USER_VS. Macros or Preprocessor Directives in C++ are instructions to the compiler. A small bolt/nut came off my mtn bike while washing it, can someone help me identify it? Stringizing in C involves more than putting double-quote characters You can't call a constexpr function from the preprocessor; constexpr isn't even recognized as a keyword until translation phase 7. Using const keyword. This is called stringizing. Not even in C11. Quoting from Shafik Yaghmour's answer at: Computing length of a C string at compile time. Received a 'behavior reminder' from manager. For token concatenation, see: https://gcc.gnu.org/onlinedocs/cpp/Concatenation.html, For token string conversion, see: https://gcc.gnu.org/onlinedocs/cpp/Stringification.html#Stringification. Connect and share knowledge within a single location that is structured and easy to search. Add a new light switch in line with another switch? The last four-line block is from Jesses answer. stringizes to "\n". Thanks to @MatteoItalia for the C++11 quote. And again, it works because you are NOT comparing strings in the. A conditional is a directive that instructs the preprocessor to select whether or not to include a chunk of code in the final token stream passed to the compiler. We use it to define a name for particular value/constant/expression. I did not know this, but it's very useful, thank you for telling us about it! There. Concatenate int to string using C Preprocessor. Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. The C99 standard 5.1.1.2 defines translation phases for C code. There is an issue passing to stringize only the outer CAT is applied (On windows at least). Does balls to the wall mean full speed ahead or full speed ahead and nosedive? There are two simple ways in C to define constants Using #define preprocessor. It contains well written, well thought and well explained computer science and programming articles, quizzes and practice/competitive programming/company interview Questions. rev2022.12.9.43105. one or more preprocessing tokens where the beginning token is not a standard-defined . UPDATE: I don't think you will be able to do it with C pre-processor. In C++11. The preprocessing directives control the behavior of the preprocessor. . xstr, so it is completely macro-expanded before xstr So you must either use a function like printf or a variable rather than the preprocessor, or pull the token out of the string like so: Thanks for contributing an answer to Stack Overflow! Preprocessing is defined by the first four (of eight) phases of translation specified in the C Standard. It would be handy if the question would include a bit more information about the desired vs. actual behavior. 10.2 Here are some cute preprocessor macros: #define begin { #define end } With these, I can write C code that looks more like Pascal. It would also be helpful to concatenate only once - consider addition of search paths "-I../icons/" rather than adding paths to the resource names. Your issue is that the preprocessor will (wisely) not replace tokens that are inside string literals. Then you can add an #else clause to the end of your #elsif list to catch cases where USER is accidentally set to something you don't know how to handle. In examples seems you could just perform Putting it all together, we have these 6 macros: Obligatory godbolt link: https://godbolt.org/z/8WGa19. (C++11, [lex.string] 13) Notice that the concatenation is not done by the preprocessor, but by the processor (the preprocessor ends its work at phase 4). Are defenders behind an arrow slit attackable? Therefore, by the time C #include with programming examples for beginners and professionals covering concepts, control statements, c array, c pointers, c structures, c union, c strings and more. Just my 2 cents. - swestrup Feb 25, 2010 at 17:45 1 It is called a macro processor because it allows you to define macros , which are brief abbreviations for longer constructs. Ready to optimize your JavaScript with Rust? Strings have much more overhead than integers or enums and if you don't need to do anything more than compare them, then strings are the wrong solution. . Thanks for contributing an answer to Stack Overflow! Not sure if it was just me or something she sent to the whole team. Remove comments and replaces them by a single space. These preprocessor directives extend only across a single line of code. Working of C Preprocessor. The table (macros jack_VS and queen_VS) which is much easier to maintain than the if-then-else construction of the OP is from Jesse. For example I could do #define name "George" and every time the preprocessor finds 'name' in the program it will replace it with "George". How do I iterate over the words of a string? C ,c,macros,c-preprocessor,variadic,variadic-macros,C,Macros,C Preprocessor,Variadic,Variadic Macros,printf #define log(fmt_string, .) #error xxx is just to see what compiler really does. purposes, is use the preprocessor to generate a compile-. The token pasting ( ##) operator simply eliminates any white space around it and concatenates (joins together) the non-whitespace characters together. with the literal text of the actual argument, converted to a string The preprocessor can be used to replace certain keywords with other words using #define. fprintf. Help us identify new roles for community members, Proposing a Community-Specific Closure Reason for non-English content. Jesses simple concatenate/stringify macro-solution fails with gcc 5.4.0 because the stringization is done before the evaluation of the concatenation (conforming to ISO C11). Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. However, this only seems to work with code. Connect and share knowledge within a single location that is structured and easy to search. constant. Computing length of a C string at compile time. Note that the commas and single quotation marks will remain visible, when printing macros like these in pragma message (I guess it might be possible to use variadic macros/__VA_ARGS__ to make a macro, that would loop through the character array values and concatenate them in a more readable manner, but the above technique is good enough for me). I have to do something like this in C. It works only if I use a char, but I need a string. I had the following work using the additional search path. How to use a VPN to access a Russian website that is banned in the EU? Subsection 6 states: Adjacent string literal tokens are concatenated. EDIT: upon further investigation, it look like this is a toolchain extension, not GCC extension, so take that into consideration You can't do that if USER is defined as a quoted string. This is the most complicated of the preprocessor directives (a little over 7 pages is devoted to it in the C99 spec and the C++98 spec devotes about 4 pages to it). The stringization macros (S() and S_()) are from Jesse. However, is it a normal feature of c preprocessor? Sudo update-grub does not work (single boot Ubuntu 22.04), Connecting three parallel LED strips to the same power supply, What is this fallacy: Perfection is impossible, therefore imperfection should be overlooked. never appear in stringized text. Never use a string when a simple value will do. To learn more, see our tips on writing great answers. The C ), This works nicely, until I try to actually, This is certainly not standard C, and I don't see how it would work with any compiler. Why is the federal judiciary of the United States divided into circuits? How do I use extern to share variables between source files? Making statements based on opinion; back them up with references or personal experience. The #define Preprocessor Given below is the form to use #define preprocessor to define a constant #define identifier value The following example explains it in detail Live Demo How to set a newcommand to be incompressible by justification? Counterexamples to differentiation under integral sign, revisited. Here is how it is done: I just thought I would add an answer that cites the source as to why this works. c++/ macros/ c-preprocessor. @AshodApakian: "Resource files" are not a feature of the C language. Why do I need double layer of indirection for macros? All preprocessor directives begin with #, and only white-space characters may appear before a preprocessor directive on a line. Improve INSERT-per-second performance of SQLite, How to generate custom StyleCop rule for C# - Conditional Compilation Preprocessor Directives, Advantages of conditional-preprocessor over conditional statements. Token-splicing, where you combine an identifier with another identifier by just concatenating their characters. string constants and stringized arguments. Pulled the following from boost, example using windows msvc which is using an additional level of indirection than what I have seen in most places. Asking for help, clarification, or responding to other answers. For example, When we try to compile a program, preprocessor commands are executed first and then the program gets compiled. @JesseChisholm, did you check your C++11 version? While the code will compile, it won't give you the expected result. Name of a play about the morality of prostitution (kind of). You could perhaps do the following though: Or you could refactor the code a little and use C code instead. How do I concatenate const/literal strings in C? The trick when working with pre-processor macros is then to not use strings as input starting point, the pre-processor doesn't know how to remove quotes. EDIT: as requested, add quotes from C and C++ Standard. Then you rely upon another feature of the preprocessor, namely that adjacent literal strings are merged into a single string. This class manages a variable name (string), description (string), and value . Did neanderthals need vitamin C from the diet? #define preprocessor directive is the most useful preprocessor directive in C language. If you really must do compile time sting comparisons, then you need to change to C++11 or newer variants that allow that feature. my_log(fmt_string, pack_args(__VA_ARGS__), __VA_ARGS__) pack_args- You're most likely used to using the preprocessor to include files directly into other files, or #define constants, but the preprocessor can also be used to create "inlined" code using macros expanded at compile time and to prevent code from being compiled twice. "p=\"foo\\n\";". For instance, I have tested the following code in https://replit.com/languages/c : So, if the tested macro and the value macros are defined as lists of character values, then they can be compared directly in a preprocessor #if conditional - and in order to print such macros in a pragma message, use of stringifying macros are required. Are defenders behind an arrow slit attackable? Would it be possible, given current technology, ten years, and an infinite amount of money, to construct a 7,000 foot (2200 meter) aircraft carrier? CSQRxX * X = 33 +1 * 3 +175 For example I could do #define name "George" and every time the preprocessor finds 'name' in the program it will replace it with "George". Why is the != operator not allowed with OpenMP? s is stringized when it is used in str, so it is not However, backslashes that are not inside string How to check whether a string contains a substring in JavaScript? So all we have to do is pick it out. So the preprocessor is looking for '$USER_JACK' variable, not finding it & giving it the default value of 0. MSVC Update: You have to parenthesize slightly differently to make things also work in MSVC. What is the difference between #include and #include "filename"? Is this really a question about resource files, and not C? Trigraph replacement: The preprocessor replaces trigraph sequences with the characters they represent. Is this really a constexpr? We can give some instructions to the compiler so that before the compiler starts compiling a program, it can follow those instructions and perform those instructions. #define square (x) x * x. but they're not always working. All leading and trailing whitespace in text being stringized is The string constant can be created with stringification, and the function name by concatenating the argument with _command. I know technically this isn't answering the OP's question, but in looking at the answers above, I am realizing (from what I can understand) that there isn't any easy way to do string comparison in the preprocessor without resorting to some "tricks" or other compiler specific magic. @AaronMcDaid the canonical K&R version of hello world is. How do I replace all occurrences of a string in JavaScript? Best way to concatenate #define to "string" I have some code as such Code: ? Does a 120cc engine burn 120cc of fuel a minute? The C Preprocessor. They are intended as a simple and portable way to detect the presence of said features. macro-expanded first. The problem with that is that a partial string literal, containing an unmatched " character, cannot be a valid preprocessing token. Use constants to provide meaningful names instead of numeric literals ("magic numbers") for special values. C language Preprocessor The preprocessor supports text macro replacement and function-like text macro replacement. So If you want to stringize the result of expansion of a macro argument, I'm compiling a source with preprocessor tokens defined in CFLAGS:-D X=string1 -D Y=string2. MOSFET is getting very hot at high frequency PWM. Not sure if this was evil, brilliant, or both, but it was exactly what I was looking for - thank you! A macro which takes the name of a command as an argument can make this unnecessary. How to set a newcommand to be incompressible by justification? EDIT: According to the comment of @Jean-Franois Fabre I adapted my answer. The basic technique for converting a value into a string in the C pre-processor is indeed via the '#' operator, but a simple transliteration of the proposed solution gets a compilation error: #define TEST_FUNC test_func #define TEST_FUNC_NAME #TEST_FUNC #include <stdio.h> int main (void) { puts (TEST_FUNC_NAME); return (0); } itself is expanded (see Argument Prescan). you have to use two levels of macros. The C preprocessor modifies a source code file before handing it over to the compiler. The #define creates a macro, which is the association of an identifier or parameterized identifier with a token string. Windows resource files don't understand the C style literal string concatenation for most elements - string table may be the only exception. Syntax to define a MACRO using #define I still make that possible (and also constrain the variables using CMake's CACHE STRINGS Property), but then convert the string to an integer before passing it as a compiler definition. For C (quoting C99, but C11 has something similar in 6.4.5p5): (C99, 6.4.5p5) "In translation phase 6, the multibyte character sequences specified by any sequence of adjacent character and identically-prefixed string literal tokens are concatenated into a single multibyte character sequence. String. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. If the header file is inside brackets, only these directories are searched. Can a prospective pilot be negated their certification because of too big/small hands? I'm trying to create a string literal in my header file that combines these two values and use it in my sources like: printf("%s", COMBINED); But this doesn't work: #define _COMBINED(x, y) x ## y #define COMBINED _COMBINED(X, Y) Thanks Definitions for the grammar summary Terminals are endpoints in a syntax definition. C Preprocessor. Why does the distance from light to subject affect exposure (inverse square law) while from subject to lens does not? 9 GCCxx - Preprocessor macro GCC: pasting x and x does not give a valid preprocessing token . In C# the #define preprocessor directive cannot be used to define constants in the way that is typically used in C and C++. How to compare strings in C conditional preprocessor-directives. rev2022.12.9.43105. You can see the intermediate steps in the above diagram. The preprocessor directives give instruction to the compiler to preprocess the information before actual compilation starts. How does the Chameleon's Arcane/Divine focus interact with magic item crafting? The user #defines the chipset they are working on when they reference the library, and the library #includes the right files. A Computer Science portal for geeks. It looks like this (string literals not concatenated by the resource compiler) is indeed the case, unfortunately: ok but how does it work in a RC file ( resource ) at the moment i have 1000 ICON "../icons/59.ico" resource number 1000 is this icon, but i want to do 1000 ICON ICON_FILE. For example: So now it is just a question of setting up the definitions appropriately. Penrose diagram of hypothetical astrophysical white hole. During the preprocessing stage, the C preprocessor (a part of the C compiler) simply substitutes the body of the macro wherever its name appears. These macro definitions allow constant values to be declared for use throughout your code. Not the answer you're looking for? Asking for help, clarification, or responding to other answers. Books that explain fundamental chess concepts. Allows what appears as symbolic macro value comparison. t.Start(); DuffsDevice(from, to, SIZE); PrintTime (std::string("Duff Device ")); t.Start(); DuffsDeviceMACRO(from, to, SIZE); PrintTime (std::string("Duff Device MACRO")); // void *memmove(void *dest, const void *src, size_t n); // DESCRIPTION // The memmove() function copies n bytes from memory area src to memory area dest. #define identifier token-string opt #define identifier (identifier opt,. Here is a sample code which I want to work --------- #ifdef LOWER #define NORMAL (x) MKLOWER (x) #else (GCC), C/C++ preprocessor directive check defined and string not empty, Comparing Objective-C Precompile Macros within Code, Can a MACRO be compared in #if with non numeric value, C/C++ Passing Macros that take arguments on the compile line. CAVEAT: Not all compilers implement the C++11 specification in the same way. https://gcc.gnu.org/onlinedocs/cpp/Concatenation.html, https://gcc.gnu.org/onlinedocs/cpp/Stringification.html#Stringification. section 5.19 Constant expressions that says this though: []>[ Note: Constant expressions can be evaluated during The do and while (0) are a kludge to make it possible to Debian/Ubuntu - Is there a man page listing all the version codenames/numbers? In this article. Here Subsection 6 states: 6 Adjacent ordinary string literal tokens are concatenated. character constants, in order to get a valid C string constant with the Later, when the stringify macro is used as S(USER_VS) the value of USER_VS (jack_VS in this example) is passed to the indirection step S_(jack_VS) which converts its value (queen) into a string "queen". Never use a string when a simple value will do. Finally, the next four-line block invokes the function-style macros. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. define. So, if you have "abc" "def", this is the same as "abcdef". For Example. 1000 ICON "../icons/22.ico". Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Not the answer you're looking for? When should static_cast, dynamic_cast, const_cast, and reinterpret_cast be used? You have to make sure that the rest of the file expands correctly. I do not want to manually search the string for keywords and then replace them, but instead want to use the preprocessor to just switch the words. How do I iterate over the words of a string? The EXPANSION* macros look like this: The answere by Patrick and by Jesse Chisholm made me do the following: Instead of #define USER 'Q' #define USER QUEEN should also work but was not tested also works and might be easier to handle. replaces the stringized arguments with string constants. When a macro We do not currently allow content pasted from ChatGPT on Stack Overflow; read our policy here. If x were a macro, it would be expanded in the Constant expressions are not guaranteed to be evaluated at compile . rev2022.12.9.43105. I am using C++ but C solutions are also acceptable. Making statements based on opinion; back them up with references or personal experience. The following worked for me with clang. This C tutorial explains how to use the #define preprocessor directive in the C language. Subsection 6 states: Similarly, in the C++ standards (ISO 14882) 2.1 defines the Phases of translation. write WARN_IF (arg);, which the resemblance of I am working on an STM32 Simulink library for a host of projects. The C preprocessor is a micro processor that is used by compiler to transform your code before compilation. #define PIE 3.141 #define ZERO 0 C Program to show use of #define Preprocessor Directives Here Subsection 6 states: 6 Adjacent ordinary string literal tokens are concatenated. Any sequence of whitespace in the middle of the text is Thus, you will always have USER_VS defined as USER_QUEEN regardless of strcmp, Delightfully convoluted! Instead, you can write a series of adjacent These transformations can be the inclusion of header files, macro expansions, etc. How do I replace all occurrences of a string in JavaScript? If you set USER to queen then the final result is the string "jack". the closest I just got was by doing this: But the ICON_FILE macro expands to "../icons/" "22" ".ico", which is valid syntax for C (adjacent string literals are concatenated), but probably not for a .rc file, which explains the "can't open icon file" message you're getting. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. For long-winded reasons, we'll need two macros for the last step; they'll be EXPANSION2 and EXPANSION3, even though one seems unnecessary. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. This allows you to expand specific identifiers into varying numbers of commas, which will become your string comparison. . After the macro is defined, the compiler can substitute the token string for each occurrence of the identifier in the source file. What REALLY happens when you don't free after malloc before program termination? Swallowing the Semicolon. As the name suggests, Preprocessors are programs that process our source code before compilation. Consider writing a program (script, whatever) that generates the appropriate #define directives for you. It looks like you're trying to use token-pasting to generate a string literal. Strings have much more overhead than integers or enums and if you don't need to do anything more than compare them, then strings are the wrong solution. The preprocessor around the fragment. The preprocessor can be used to replace certain keywords with other words using #define. The C preprocessor provides four separate facilities that you . All preprocessor directives starts with hash # symbol. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. [2021.01.04: CAVEAT: This does not work in any MODERN compiler. Preprocessing is done in translation phase 4. after prepocess // still have #line, #pragma, etc) // #define STB_C_LEX_ISWHITE(str) . How can I do this? How to check whether a string contains a substring in JavaScript? Does Python have a string 'contains' substring method? You can't do compile time string compares in C99, but you can do compile time choosing of strings. 4. 10.1 I'm trying to define a few simple little function-like macros such as. UPD This example looks like working now. long string. Comments are 1980s short story - disease of self absorption, Name of a play about the morality of prostitution (kind of), Typesetting Malayalam in xelatex & lualatex gives error. ", (C++11, 2.14.5p13) "In translation phase 6 (2.2), adjacent string literals are concatenated.". There probably needs to be a table of commands, perhaps an array of structures declared as follows: It would be cleaner not to have to give each command name twice, once in the string constant and once in the function name. However, there is one caveat: it will not work if passed another macro. instead of the name of the macro. C preprocessor processes the defined name and replace each occurrence of a particular string/defined name (macro name) with a given value (micro body). Select the Configuration Properties > C/C++ > Preprocessor property page. (since C++20) Example Run this code We do not currently allow content pasted from ChatGPT on Stack Overflow; read our policy here. Find centralized, trusted content and collaborate around the technologies you use most. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Connect and share knowledge within a single location that is structured and easy to search. As soon as a newline character is found, the preprocessor directive is ends. # define STB_C_LEX_DISCARD_PREPROCESSOR Y // discard C-preprocessor directives (e.g. But, as @Artyer points out, the version involving c_strcmp will NOT work in ANY modern compiler. The preprocessor examines the code before actual compilation of code begins and resolves all these directives before any code is actually generated by regular statements. Answer: I don't think C specifies the difference, but there is a common behavior which I will describe. Replacing cat definition with #define cat(a,b) a ## b breaks things. However, the problem of assigning a macro with the opposite value can be solved with token pasting and table access. 3 Answers. Can virent/viret mean "green" in an adjectival sense? It should not provide the default constructor. So while technically this solution isn't comparing strings, syntactically it kind of behaves/looks the same. Why are these constructs using pre and post-increment undefined behavior? Hey Mugsy: Did you ever figure this out? Sed based on 2 words, then replace whole line with variable. Q: What does the preprocessor do? Likewise, if you have macros for A and B, then #A #B would concatenate them. For example, this code should produce the version_string that you're seeking: To learn more, see our tips on writing great answers. If you want help with them, you'll need to tell us what environment you're using. How to smoothen the round border of a created buffer to make it look more natural? See Feature testing for details. This gives the opportunity to add a number of commas according to whether or not a string matches: If USER is JACK, JACK_QUEEN_OTHER(USER) becomes EXPANSION2(x,x,x, 1, 2, 3), If USER is QUEEN, JACK_QUEEN_OTHER(USER) becomes EXPANSION2(x,x, 1, 2, 3), If USER is other, JACK_QUEEN_OTHER(USER) becomes EXPANSION2(ReSeRvEd_other, 1, 2, 3). This flat-out wrong answer has already misled someone who referenced it. rev2022.12.9.43105. macro-expanded first. Why is char[] preferred over String for passwords? I've wanted to use string comparison as well in preprocessor macros, mostly so I can also "print" these values during preprocessing step (using pragma message). All preprocessing directives begin with a # symbol. What is the difference between String and string in C#? With a little massaging, you could get it to work though. time, we only have a non-normative quote from draft C++ standard The preprocessors are the directives, which give instructions to the compiler to preprocess the information before actual compilation starts. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Conditionals . How do I make the first letter of a string uppercase in JavaScript? turns that into EXPANSION1(ReSeRvEd_, JACK, 1, 2, 3), Now JACK_QUEEN_OTHER(USER) becomes EXPANSION2(ReSeRvEd_JACK, 1, 2, 3). replaced by whitespace long before stringizing happens, so they Other useful modules include Foreign.C.String, . parameter is used with a leading #, the preprocessor replaces it Joins any lines that end with a backslash character into a single line. Two strings that are next to each other in C are treated as a single string and automatically concatenated. 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