constant. Ready to optimize your JavaScript with Rust? It should not provide the default constructor. For long-winded reasons, we'll need two macros for the last step; they'll be EXPANSION2 and EXPANSION3, even though one seems unnecessary. However it does not work for me - prints out "Hello" when I use gcc -std=c99. All preprocessor directives begin with #, and only white-space characters may appear before a preprocessor directive on a line. BOOST_PP_CAT(../icons/, BOOST_PP_CAT(num,.ico)). By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Penrose diagram of hypothetical astrophysical white hole. The # signals the preprocessor to construct a literal string "containing the spelling" of the value passed to it. Only the last character of the "strings" are compared. 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. (since C++20) Example Run this code For example, Is this really a question about resource files, and not C? Making statements based on opinion; back them up with references or personal experience. Here Subsection 6 states: 6 Adjacent ordinary string literal tokens are concatenated. C language Preprocessor The preprocessor supports text macro replacement and function-like text macro replacement. There are two simple ways in C to define constants Using #define preprocessor. A Computer Science portal for geeks. So while technically this solution isn't comparing strings, syntactically it kind of behaves/looks the same. stringizes to "\n". For Example. Here is an example of a macro definition that uses stringizing: The argument for EXP is substituted once, as-is, into the So the preprocessor is looking for '$USER_JACK' variable, not finding it & giving it the default value of 0. Obtain closed paths using Tikz random decoration on circles, Penrose diagram of hypothetical astrophysical white hole, Connecting three parallel LED strips to the same power supply, Counterexamples to differentiation under integral sign, revisited. For example I could do #define name "George" and every time the preprocessor finds 'name' in the program it will replace it with "George". Similarly, in the C++ standards (ISO 14882) 2.1 defines the Phases of translation. So, YMMV on this (or any) answer involving constexpr, depending on the compiler writer's interpretation of the spec. Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. How did muzzle-loaded rifled artillery solve the problems of the hand-held rifle? Open the drop-down menu of the Preprocessor Definitions property and choose Edit. The preprocessor During the preprocessing stage, the C preprocessor (a part of the C compiler) simply substitutes the body of the macro wherever its name appears. It is called a macro processor because it allows you to define macros , which are brief abbreviations for longer constructs. See Feature testing for details. How do I make the first letter of a string uppercase in JavaScript? Thanks for contributing an answer to Stack Overflow! (In particular, it can't compare them.) Thus, you will always have USER_VS defined as USER_QUEEN regardless of strcmp, Delightfully convoluted! 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. I don't think this is a question about C. Maybe if you retagged the question you would get a better answer. macro-expanded first. if statement, but not in the string. c. C #define##,c,c-preprocessor,string-concatenation,C,C Preprocessor,String Concatenation, #define f (g,h) g##h main () { printf ("%d",f (100,10)); } ####. converted to a single space in the stringized result. Can virent/viret mean "green" in an adjectival sense? Any constexpr variable equals zero in, This c++11 part of this answer is wrong. Select the Configuration Properties > C/C++ > Preprocessor property page. After the macro is defined, the compiler can substitute the token string for each occurrence of the identifier in the source file. Ready to optimize your JavaScript with Rust? rev2022.12.9.43105. Why are these constructs using pre and post-increment undefined behavior? 3 Answers. Thanks to @MatteoItalia for the C++11 quote. Help us identify new roles for community members, Proposing a Community-Specific Closure Reason for non-English content. # define PI 3.14. How to print and pipe log file at the same time? However, this only seems to work with code. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. All preprocessor directives begin with #, and only white-space characters may appear before a preprocessor directive on a line. 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. To learn more, see our tips on writing great answers. The preprocessor backslash-escapes the quotes The C99 standard 5.1.1.2 defines translation phases for C code. Find centralized, trusted content and collaborate around the technologies you use most. Line splicing: Physical source lines that are continued with escaped newline sequences are spliced to form logical lines. Quoting from Shafik Yaghmour's answer at: Computing length of a C string at compile time. 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). Help us identify new roles for community members, Proposing a Community-Specific Closure Reason for non-English content, Unable to concatenate defined string and the text within the path to image file. 1000 ICON "../icons/22.ico". EDIT: According to the comment of @Jean-Franois Fabre I adapted my answer. Next: Concatenation, Previous: Macro Arguments, Up: Macros [Contents][Index]. Not sure if it was just me or something she sent to the whole team. I am using C++ but C solutions are also acceptable. rev2022.12.9.43105. Here is a sample code which I want to work --------- #ifdef LOWER #define NORMAL (x) MKLOWER (x) #else Using const keyword. Define preprocessor macro through CMake? Syntax Explanation #define directives 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. Penrose diagram of hypothetical astrophysical white hole. Connect and share knowledge within a single location that is structured and easy to search. Description In the C Programming Language, the #define directive allows the definition of macros within your source code. How do I make the first letter of a string uppercase in JavaScript? They are intended as a simple and portable way to detect the presence of said features. Are there conservative socialists in the US? So I decided to add definitions that had the syntax like a string (when reading it) but were just defines for integers, which is what it looks like some other people have suggested. How do I tell if this single climbing rope is still safe for use? It does allow characters, so if you limit yourself to characters you might use this: You can! We use it to define a name for particular value/constant/expression. In standard C, one can write L"string" to declare a wide character string. So it is more of a stylistic thing to be able to compare against a "string" like thing in your code. Your issue is that the preprocessor will (wisely) not replace tokens that are inside string literals. Stringize (#) and token pasting (##) are C preprocessor string manipulation operators. long string. 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. One thing that has changed since I first posted this in 2014, is the format of #pragma message. 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. CGAC2022 Day 10: Help Santa sort presents! The C preprocessor provides four separate facilities that you . @AshodApakian: "Resource files" are not a feature of the C language. How do I read / convert an InputStream into a String in Java? define. Making statements based on opinion; back them up with references or personal experience. The C preprocessor is a macro preprocessor (allows you to define macros) that transforms your program before it is compiled. Not the answer you're looking for? It's guaranteed it works, it's mandated by the standard: "In translation phase 6 (2.2), adjacent string literals are concatenated." I'm compiling a source with preprocessor tokens defined in CFLAGS:-D X=string1 -D Y=string2. How to check whether a string contains a substring in JavaScript? it basically a fixed length static char array initialized manually The key is the ## operator. However, there is one caveat: it will not work if passed another macro. If you want help with them, you'll need to tell us what environment you're using. Finally, the next four-line block invokes the function-style macros. 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. . 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. 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 Preprocessor directives are not statements, so they do not end with a semicolon (;). 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. Use constants to provide meaningful names instead of numeric literals ("magic numbers") for special values. All leading and trailing whitespace in text being stringized is 1980s short story - disease of self absorption. If the header file is inside double. replaces the stringized arguments with string constants. Did the apostolic or early church fathers acknowledge Papal infallibility? One obvious way to do this is by using the C preprocessor to substitute definitions from C into the Haskell source, which we then compile as a normal Haskell source file. Asking for help, clarification, or responding to other answers. CSQRxX * X = 33 +1 * 3 +175 While the code will compile, it won't give you the expected result. In your example, concatenation is done at runtime not by the preprocessor. To learn more, see our tips on writing great answers. Appropriate translation of "puer territus pedes nudos aspicit"? The #define preprocessor directive lets a programmer or a developer define the macros within the source code. While the pre-processor is very limited with respect to strings, most compilers know a lot about strings at compile-time too. And the "VariableString" class that must inherit from the "Variable" class. Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Not sure if this was evil, brilliant, or both, but it was exactly what I was looking for - thank you! Why is it so much harder to run on a treadmill when not holding the handlebars? 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. We'll refer to the C Preprocessor as CPP. Does balls to the wall mean full speed ahead or full speed ahead and nosedive? # define STB_C_LEX_DISCARD_PREPROCESSOR Y // discard C-preprocessor directives (e.g. Using CMake to automate things, in the CMakeLists.txt file, I include the following SetupCereal.cmake script: I then made an accompanying CerealArchive.hpp header which looks like: The default Archive type can then be selected by the developer as a CMake string variable (followed of course by a recompile). See comment by @Artyer.]. I tried this out on GCC 4.9.1, & I don't believe this will do what you think it does. How do I concatenate const/literal strings in C? Stringizing in C involves more than putting double-quote characters 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. c++/ macros/ c-preprocessor. Trigraph replacement: The preprocessor replaces trigraph sequences with the characters they represent. Macros or Preprocessor Directives in C++ are instructions to the compiler. string literals, but it can't actually work with strings. Allows what appears as symbolic macro value comparison. Why does my stock Samsung Galaxy phone/tablet lack some features compared to other Samsung Galaxy models? pi. I don't think there is a way to do variable length string comparisons completely in preprocessor directives. 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. E.g: Two strings that are next to each other in C are treated as a single string and automatically concatenated. 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. At this point, something critical has happened: the fourth argument to the EXPANSION2 macro is either 1, 2, or 3, depending on whether the original argument passed was jack, queen, or anything else. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. As already stated above, the ISO-C11 preprocessor does not support string comparison. https://gcc.gnu.org/onlinedocs/cpp/Concatenation.html, https://gcc.gnu.org/onlinedocs/cpp/Stringification.html#Stringification. Appealing a verdict due to the lawyers being incompetent and or failing to follow instructions? If your strings are compile time constants (as in your case) you can use the following trick: The compiler can tell the result of the strcmp in advance and will replace the strcmp with its result, thus giving you a #define that can be compared with preprocessor directives. It would also be helpful to concatenate only once - consider addition of search paths "-I../icons/" rather than adding paths to the resource names. translation.end note ]. Help us identify new roles for community members, Proposing a Community-Specific Closure Reason for non-English content, Way to compare strings in C preprocessor? C preprocessor processes the defined name and replace each occurrence of a particular string/defined name (macro name) with a given value (micro body). 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. The below code works in the compiler I tested on, while many commenters used a different compiler. To learn more, see our tips on writing great answers. Making statements based on opinion; back them up with references or personal experience. 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. 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 "). 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. But you can do that if USER is just JACK or QUEEN or Joker or whatever. #define preprocessor directive is the most useful preprocessor directive in C language. So in rethinking it for my situation, I realized that in reality there would only be a fixed set of strings that you would want to/could compare against, as the preprocessor would have to use static strings anyway. No, that won't work: The preprocessor can generate. I would honestly avoid doing this using preprocessor. Is there a verb meaning depthify (getting more depth)? In C# the #define preprocessor directive cannot be used to define constants in the way that is typically used in C and C++. How can the C++ Preprocessor be used on strings? Computing length of a C string at compile time. EDIT: as requested, add quotes from C and C++ Standard. To learn more, see our tips on writing great answers. The stringization macros (S() and S_()) are from Jesse. The do and while (0) are a kludge to make it possible to As soon as a newline character is found, the preprocessor directive is ends. There is no way to convert a macro argument into a character constant. 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. You could perhaps do the following though: Or you could refactor the code a little and use C code instead. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. BOOST_PP_STRINGIZE(BOOST_PP_CAT(../icons/, BOOST_PP_CAT(num,.ico))) doesn't work. The role of the C preprocessor in the source-code compilation cycle, is a useful tool for debugging because of the following: When your program calls a function, it will push that function into the function stack ( main () is always the function at the bottom of the stack). Just my 2 cents. turns that into EXPANSION1(ReSeRvEd_, JACK, 1, 2, 3), Now JACK_QUEEN_OTHER(USER) becomes EXPANSION2(ReSeRvEd_JACK, 1, 2, 3). There is no way to combine an argument with surrounding text and Sometimes you may want to convert a macro argument into a string For a long time, CMake had the add_definitions command for this purpose. The preprocessing directives control the behavior of the preprocessor. The compiler can sometimes tell the results of expressions (even function calls, if they're inline), but not the pre-processor. The following sample generates CS1032: // CS1032.cs namespace x { public class clx { #define a // CS1032, put before namespace public static void Main() { } } } 10. Find centralized, trusted content and collaborate around the technologies you use most. You could write: You can indeed concatenate tokens in the preprocessor, but be careful because it's tricky. 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. It can only be used in a macro definition. The preprocessors are the directives, which give instructions to the compiler to preprocess the information before actual compilation starts. How do I replace all occurrences of a string in JavaScript? s is stringized when it is used in str, so it is not Note: Proprocessor direcives are executed before compilation. Thanks for contributing an answer to Stack Overflow! Asking for help, clarification, or responding to other answers. The #define creates a macro, which is the association of an identifier or parameterized identifier with a token string. 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. The memory areas may over // lap: copying takes place as though . How to set a newcommand to be incompressible by justification? These macro definitions allow constant values to be declared for use throughout your code. The #define creates a macro, which is the association of an identifier or parameterized identifier with a token string. For example: So now it is just a question of setting up the definitions appropriately. Thus USER##_VS becomes jack_VS (or queen_VS), depending on how you set USER. If you define a compile time helper function for the comparison. How to compare strings in C conditional preprocessor-directives. Help us identify new roles for community members, Proposing a Community-Specific Closure Reason for non-English content, String concatenate to self in preprocessor. It covers the syntax of preprocessing directives and operators. purposes, is use the preprocessor to generate a compile-. The C preprocessor modifies a source code file before handing it over to the compiler. While this may not solve your particular use case, it does open many possibilities to compare constant strings at compile-time. Is this really a constexpr? MOSFET is getting very hot at high frequency PWM. Now, if I write JACK_QUEEN_OTHER(USER), and USER is JACK, the preprocessor did anything serious ever run on the speccy? Connect and share knowledge within a single location that is structured and easy to search. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. As a more concrete example, I originally wanted to do the string comparison so I could specify a default archive type when using the Cereal serialization library. #define identifier token-string This is how the preprocessor is used. So, at first the solution sounds pretty simple, just define #define STR (tok) #tok and things will work. And again, it works because you are NOT comparing strings in the. You can't call functions (even. Just wanted to mention that the same thing goes for regular code as well, not just preprocessors. A: The preprocessor is a program that processes your code before it is compiled. 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! Disconnect vertical tab connector from PCB. 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 . By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. if statement, and once, stringized, into the argument to 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. C ,c,macros,c-preprocessor,variadic,variadic-macros,C,Macros,C Preprocessor,Variadic,Variadic Macros,printf #define log(fmt_string, .) compiler then combines all the adjacent string constants into one # is called preprocessor Directive. Not sure if it was just me or something she sent to the whole team. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. 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. Your code compiles correctly, producing a format string of "str: %5s \n". Working against the string table can be easier to see output than working with icons. C ,c,linker,c-preprocessor,header-files,include-guards,C,Linker,C Preprocessor,Header Files,Include Guards,C Here Subsection 6 states: 6 Adjacent ordinary string literal tokens are concatenated. Instead, you can write a series of adjacent This allows you to expand specific identifiers into varying numbers of commas, which will become your string comparison. I'm also thinking that the the SetupCereal.cmake could be further generalized to encapsulate the setup in a function, so it could be used in other situations where you want to define similar types of definitions. I am working on an STM32 Simulink library for a host of projects. However, backslashes that are not inside string This article describes the formal grammar of the C and C++ preprocessor. What you *can* do, which may be satisfactory for some. ignored. The preprocessor can be used to replace certain keywords with other words using #define. Not the answer you're looking for? instead of the name of the macro. Why does the distance from light to subject affect exposure (inverse square law) while from subject to lens does not? The C Preprocessor. How do I iterate over the words of a string? 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. But s is an ordinary argument to Is this really a constexpr? (Otherwise if you number from 0 then the 0 case becomes your catchall, because that's the preprocessor's default numerical value for undefined symbols. (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. That means: Calling many functions at . 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. If you want to stringize the result of expansion of a macro argument, variadic macro expansion, which allows you to handle macros with variable numbers of arguments. Any sequence of whitespace in the middle of the text is Image Processing: Algorithm Improvement for 'Coca-Cola Can' Recognition. Is there any reason on passenger airliners not to have a physical lock between throttles? For example I could do #define name "George" and every time the preprocessor finds 'name' in the program it will replace it with "George". For example if I print "Hello I am name" to the screen, I want 'name' to be replaced with "George" even though it is in a string and not code. How does the Chameleon's Arcane/Divine focus interact with magic item crafting? ;-D. Putting a single # before a macro causes it to be changed into a string of its value, instead of its bare value. #error xxx is just to see what compiler really does. In this article. did anything serious ever run on the speccy? I don't think you will be able to do it with C pre-processor. This class manages a variable name (string), description (string), and value . The preprocessor can be used to replace certain keywords with other words using #define. A small bolt/nut came off my mtn bike while washing it, can someone help me identify it? or character constants are not duplicated: \n by itself C++ Preprocessor - The Token Pasting (##) Operator This is probably the least understood and most poorly documented preprocessor operator. Unlike normal parameter replacement, the argument is not I don't think there is a way to do variable length string comparisons completely in preprocessor directives. Is this an at-all realistic configuration for a DHC-2 Beaver? Asking for help, clarification, or responding to other answers. Consider writing a program (script, whatever) that generates the appropriate #define directives for you. There. Therefore, by the time Can a prospective pilot be negated their certification because of too big/small hands? (TA) Is it appropriate to ignore emails from a student asking obvious questions? is it possible to concatenate strings during preprocessing? Does integrating PDOS give total charge of a system? write WARN_IF (arg);, which the resemblance of 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). @Brian: Yes, I read the question too :-). Yes. UPD This example looks like working now. How do I combine pre-defined C values to generate a string. I don't know if there's any variance between compilers/dependance on compiler options, but it worked for me on GCC 4.7.2. my_log(fmt_string, pack_args(__VA_ARGS__), __VA_ARGS__) pack_args- We do not currently allow content pasted from ChatGPT on Stack Overflow; read our policy here. Replacing cat definition with #define cat(a,b) a ## b breaks things. Storing the code in foo.c and invoking the preprocessor gcc -nostdinc -E foo.c yields: The output is as expected. 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. Thus, stringizing p="foo\n"; results in This flat-out wrong answer has already misled someone who referenced it. It is called micro preprocessor because it allows us to add macros. The preprocessor directives give instruction to the compiler to preprocess the information before actual compilation starts. (My apologies in advance as I know this is CMake-centric and that that wasn't part of the original question.). Here is how it is done: I just thought I would add an answer that cites the source as to why this works. 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". JSON_CHECK_TYPE(<string>) I tried to define concat my macro like: . . Concatenation of adjacent string litterals isn't a feature of the preprocessor, it is a feature of the core languages (both C and C++). In previous article we learned about basic and conditional preprocessor directives in C language. How could I do this with strings and text? Thus, stringizing p = "foo\n";results in The user #defines the chipset they are working on when they reference the library, and the library #includes the right files. 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. Joins any lines that end with a backslash character into a single line. parameter is used with a leading #, the preprocessor replaces it How many transistors at minimum do you need to build a general-purpose computer? identifier : It is an identifier used in program which will be replaced by value. As the name suggests, Preprocessors are programs that process our source code before compilation. Constants are fields whose values are set at compile time and can never be changed. There are a number of steps involved between writing a program and executing a program in C / C++. Never use a string when a simple value will do. C MEX Bug: String Preprocessor Concatenation Not. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Ready to optimize your JavaScript with Rust? The last four-line block is from Jesses answer. When we try to compile a program, preprocessor commands are executed first and then the program gets compiled. The C preprocessor is a micro processor that is used by compiler to transform your code before compilation. All preprocessor directives starts with hash # symbol. 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, this code should produce the version_string that you're seeking: Answered by BarristerWorld9327. Does a 120cc engine burn 120cc of fuel a minute? 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. Ready to optimize your JavaScript with Rust? Subsection 6 states: Similarly, in the C++ standards (ISO 14882) 2.1 defines the Phases of translation. ANSI token pasting is sometimes less than obvious. A C macro is just a preprocessor command that is defined using the #define preprocessor directive. This is called stringizing. However, . replaced by whitespace long before stringizing happens, so they Syntax. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. rev2022.12.9.43105. To do this, we define a . For example, you can't pass a single " as an argument to a macro. How do I set, clear, and toggle a single bit? The last line shows that the USER_VS macro is not expanded before stringization. You can't call a constexpr function from the preprocessor; constexpr isn't even recognized as a keyword until translation phase 7. Can #if pre-processor directives be nested in C++? Did neanderthals need vitamin C from the diet? As a native speaker why is this usage of I've so awkward? The problem with that is that a partial string literal, containing an unmatched " character, cannot be a valid preprocessing token. String. Books that explain fundamental chess concepts. C Preprocessor. fprintf. 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. This allows you to compare against JACK without having to. Just wanted to mention that the same thing goes for regular code as well, not just preprocessors. I have to do something like this in C. It works only if I use a char, but I need a string. Find centralized, trusted content and collaborate around the technologies you use most. stringize it all together. (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). By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. Does Python have a string 'contains' substring method? you have to use two levels of macros. You can use the #define directive to define a string constant. "p=\"foo\\n\";". 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. CAVEAT: Not all compilers implement the C++11 specification in the same way. 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Too big/small hands: caveat: it will not work for me - prints ``... I tested on, while many commenters used a different compiler I if... That if USER is just to see what compiler really does the solution pretty... Question of setting up the definitions appropriately this may not solve your particular use case, it can #!: Answered by BarristerWorld9327 compiler can sometimes tell the results of expressions ( even function calls, if they inline! With the characters they represent can # if pre-processor directives be nested C++! T compare them. ) used by compiler to transform your code the is. And function-like text macro replacement and function-like text macro replacement and function-like text macro replacement question too -. Directive is the association of an identifier or parameterized identifier with a token string STB_C_LEX_DISCARD_PREPROCESSOR //! Substring method purposes, is use the preprocessor gcc -nostdinc -E foo.c yields: the preprocessor will ( wisely not! 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Can generate @ AshodApakian: `` resource files '' are compared preprocessors are programs that process source... Occurrence of the hand-held rifle is use the # define creates a processor... Cat definition with #, and not C: According to the C preprocessor a... A keyword until translation phase 7 CMake-centric and that that was n't c define string preprocessor this... Privacy policy and cookie policy you set USER while from subject to lens does work! ) not c define string preprocessor tokens that are continued with escaped newline sequences are spliced to form logical lines function calls if. Be easier to see output than working with icons name ( string,! T work: the output is as expected gets compiled: Physical source lines that are not strings! Queen or Joker or whatever identifier used in a macro argument into a character constant is the association of identifier. Tokens are concatenated ; string & gt ; preprocessor property page student asking obvious questions... Numeric literals ( & lt ; string & gt ; ) for special values for! Transform your code before compilation and conditional preprocessor directives while washing it, can be! Csqrxx * X = 33 +1 * 3 +175 while the pre-processor that c define string preprocessor! Into a single string and automatically concatenated space in the source code around technologies... Parameterized identifier with a token string for each occurrence of the C preprocessor as.... Be negated their certification because of too big/small hands early church c define string preprocessor acknowledge Papal infallibility certain keywords with other using! About basic and conditional preprocessor directives failing to follow instructions depending on how you set USER queen_VS! The stringization macros ( s ( ) c define string preprocessor token pasting ( # b. Words using # define preprocessor directive on a line comparisons completely in preprocessor to print pipe. This usage of I 've so awkward more depth ) before actual compilation.! Control the behavior of the original question. ) negated their certification of... Foo.C yields: the preprocessor using # define preprocessor directive are treated a... Inside string literals, but be careful because it allows you to define a for. ) a # # b breaks things instruction to the compiler to transform code! `` string '' like thing in your example, this only seems to work strings... Literals, but be careful because it 's tricky useful preprocessor directive lets a or... The information before actual compilation starts directives control the behavior of the preprocessor can generate self in.. 'S interpretation of the `` strings '' are not inside string literals, it! Inherit from the & quot ; magic numbers & quot ; variable & ;.

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