Macro definitions take effect at the place you write them. foo(); funcptr = foo; Here the call to foo() will use the macro, but the function pointer will get the address of the real function. Please help improve it or discuss these issues on the talk page. (Learn how and when to remove these template messages) This article is written like a manual or guidebook. Note that Clang will never emit type information for types that are not referenced at all by the program. -fno-standalone-debug¶ On Darwin -fstandalone-debug is enabled by default.
Code that is not exercised in the profile will be optimized as if it is unimportant, and the compiler may make poor optimization choices for code that is disproportionately used while If multiple flags are present, the last one is used. -g0¶ Don't generate any debug info (default). -gline-tables-only¶ Generate line number tables only. When to use "bon appetit"? In addition to controlling warnings and errors generated by the compiler, it is possible to generate custom warning and error messages through the following pragmas: // The following will produce warning
Clang has the ability to print this information, and these are the options that control it: A file/line/column indicator that shows exactly where the diagnostic occurs in your code [-fshow-column, -fshow-source-location]. This is very likely to cause an error, e.g. If it is defined, its value is 1. This option, which defaults to off, controls whether Clang prints the profile hotness associated with a diagnostics in the presence of profile-guided optimization information.
Normally, only the headers found in specific directories are considered system headers. There are, however, two ways to make normal headers into system headers. Macros A macro is a fragment of code which has been given a name. http://stackoverflow.com/questions/171435/portability-of-warning-preprocessor-directive The preprocessor simultaneously expands macros and, in the 1999 version of the C standard,[clarification needed] handles _Pragma operators.
Stringification in C involves more than putting double-quote characters around the fragment. For example, #define BUFFER_SIZE 1024 defines a macro named BUFFER_SIZE as an abbreviation for the token 1024. When a macro parameter is used with a leading #, the preprocessor replaces it with the literal text of the actual argument, converted to a string constant. In the example above an invalid directive error occurs at the incorrect usage #elseif, but only when FOO is defined (otherwise the preprocessor ignores everything up to the #else statement).
This macro exists primarily to direct GNU libc's header files to restrict their definitions to the minimal set found in the 1989 C standard. __BASE_FILE__ This macro expands to the name https://en.wikipedia.org/wiki/C_preprocessor It must always be used together with __GNUC__ and __GNUC_MINOR__. __GNUC_PATCHLEVEL__ is new to GCC 3.0; it is also present in the widely-used development snapshots leading up to 3.0 This lets you poison an identifier without worrying about system headers defining macros that use it. Retrieved 27 October 2008. ^ a b "The C Preprocessor: Overview".
This document describes important notes about using Clang as a compiler for an end-user, documenting the supported features, command line options, etc. It is called a macro processor because it allows you to define macros, which are brief abbreviations for longer constructs. This option, which defaults to on, enables warnings about extra tokens at the end of preprocessor directives. current community chat Stack Overflow Meta Stack Overflow your communities Sign up or log in to customize your list.
I'm using it to mark a section of code I'd like to come back to shortly in a very obvious way, and as a tool to communicate to other programmers - It specifies the operation to perform. You cannot simply include the old header with #include. description of local variables or function parameters). -fstandalone-debug¶ Clang supports a number of optimizations to reduce the size of debug information in the binary.
Further, Clang will only emit type info for a dynamic C++ class in the module that contains the vtable for the class. See also C syntax Make Preprocessor m4 (computer language) PL/I preprocessor References ^ List of predefined ANSI C and Microsoft C++ implementation macros. ^ Wirzenius, Lars. Instead, the preprocessor offers the ability to use a macro for the header name.
The result is then processed as if it had appeared as the right hand side of a ‘ #pragma ’ directive. Comments are replaced by whitespace long before stringification happens, so they never appear in stringified text. Controlling Code Generation¶ Clang provides a number of ways to control code generation. Parameters are not replaced inside string constants, but you can use the # preprocessing operator instead.
When the macro is invoked, all the tokens in its argument list after the last named argument (this macro has none), including any commas, become the variable argument. Their names all start with double underscores. __FILE__ __LINE__ __DATE__ __TIME__ __STDC__ __STDC_VERSION__ __STDC_HOSTED__ __FILE__ This macro expands to the name of the current input file, in the form of a Below are the command line options to control the crash diagnostics. -fno-crash-diagnostics¶ Disable auto-generation of preprocessed source files during a clang crash. For backward compatibility, pragmas which were recognized by previous versions are still recognized without the GCC prefix, but that usage is deprecated.
If the line expands to a token stream beginning with a < token and including a > token, then the tokens between the < and the first > are combined to It must always be used together with __GNUC__. __GNUC_PATCHLEVEL__ The macro contains the bugfix version number of the compiler. Pete enjoys writing excellent, bug-free code, so he can spend more time having fun with his kids. E.g.: #line 314 "pi.c" printf("line=%d file=%s\n", __LINE__, __FILE__); generates the printf function: printf("line=%d file=%s\n", 314, "pi.c"); Source code debuggers refer also to the source position defined with __FILE__ and __LINE__.
It is wisest to make the argument of these directives be a single string constant; this avoids problems with apostrophes and the like. To write standards-compliant code, you may use continued lines instead, or string constant concatenation. It is called object-like because it looks like a data object in code that uses it. For example, if you know that the program will not run properly on a VAX, you might write #ifdef __vax__ #error "Won't work on VAXen.
Create unreferenced labe like HereIsMyWarning: and don't reference it. Are you aware of (can you name) a compiler other than GCC/G++ that provides #warning? [Edited: Sun Solaris 10 (Sparc) and the Studio 11 C/C++ compilers both accept #warning.] share|improve this