Next:, Previous:, Up: [][] 7 Pragmas The ‘ #pragma’ directive is the method specified by the C standard for providing additional information to the compiler, beyond what is conveyed in the language itself. The forms of this directive (commonly known as pragmas) specified by C standard are prefixed with STDC.
Prolific USB-to-Serial if you are. Avr-gcc -mmcu=attiny2313 -Wall. Thanks to your project “Using the USART of AVR Microcontrollers: Reading and.
A C compiler is free to attach any meaning it likes to other pragmas. All GNU-defined, supported pragmas have been given a GCC prefix.
C99 introduced the _Pragma operator. This feature addresses a major problem with ‘ #pragma’: being a directive, it cannot be produced as the result of macro expansion. _Pragma is an operator, much like sizeof or defined, and can be embedded in a macro.
Its syntax is _Pragma ( string-literal), where string-literal can be either a normal or wide-character string literal. It is destringized, by replacing all ‘ ’ with a single ‘ ’ and all ‘ '’ with a ‘ '’.
The result is then processed as if it had appeared as the right hand side of a ‘ #pragma’ directive. #define DO_PRAGMA(x) _Pragma (#x) DO_PRAGMA (GCC dependency 'parse.y') The standard is unclear on where a _Pragma operator can appear. The preprocessor does not accept it within a preprocessing conditional directive like ‘ #if’. To be safe, you are probably best keeping it out of directives other than ‘ #define’, and putting it on a line of its own. This manual documents the pragmas which are meaningful to the preprocessor itself. Other pragmas are meaningful to the C or C++ compilers.
They are documented in the GCC manual. GCC plugins may provide their own pragmas. #pragma GCC dependency #pragma GCC dependency allows you to check the relative dates of the current file and another file. If the other file is more recent than the current file, a warning is issued.
This is useful if the current file is derived from the other file, and should be regenerated. The other file is searched for using the normal include search path. Optional trailing text can be used to give more information in the warning message. #define strrchr rindex #pragma GCC poison rindex strrchr(some_string, 'h'); will not produce an error.
#pragma GCC system_header This pragma takes no arguments. Ccdp Arch 642-874 Pdf Download. It causes the rest of the code in the current file to be treated as if it came from a system header. #pragma GCC warning #pragma GCC error #pragma GCC warning 'message' causes the preprocessor to issue a warning diagnostic with the text ‘ message’.
The message contained in the pragma must be a single string literal. Similarly, #pragma GCC error 'message' issues an error message. Unlike the ‘ #warning’ and ‘ #error’ directives, these pragmas can be embedded in preprocessor macros using ‘ _Pragma’.