Directive #error C
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message. You would use ‘#error’ inside of use of #error directive in c a conditional that detects a combination of #error example parameters which you know the program does not properly support. For c preprocessor error directive example, if you know that the program will not run properly on a VAX, you might write #ifdef __vax__
#error In C Example
#error "Won't work on VAXen. See comments at get_last_object." #endif If you have several configuration parameters that must be set up by the installation in a consistent way, you can use conditionals to detect an inconsistency and report #error c++ it with ‘#error’. For example, #if !defined(FOO) && defined(BAR) #error "BAR requires FOO." #endif The directive ‘#warning’ is like ‘#error’, but causes the preprocessor to issue a warning and continue preprocessing. The tokens following ‘#warning’ are used as the warning message. You might use ‘#warning’ in obsolete header files, with a message directing the user to the header file which should be used instead. Neither ‘#error’ nor ‘#warning’ macro-expands its argument. Internal whitespace sequences are each replaced with a single space. The line must consist of complete tokens. It is wisest to make the argument of these directives be a single string constant; this avoids problems with apostrophes and the like.
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our Embedded Systems Glossary. A B C D EF G H I JK L M N OP Q R S TU V
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W X YZ Symbols Test Your Skills How good are your embedded programming skills? Test yourself in the Embedded C Quiz or the Embedded C++ Quiz. Newsletter Signup Want to receive free how-to articles and industry https://gcc.gnu.org/onlinedocs/cpp/Diagnostics.html news as well as announcements of free webinars and other training courses by e-mail? Signup Today! How to Use the C Preprocessor's #error Directive Wed, 1999-09-01 00:00 - Nigel Jones by Nigel Jones One of the least used but potentially most useful features of the C preprocessor is the ANSI-specified #error directive. Here's a look at a couple of clever uses for #error that have proven invaluable in embedded software development. The http://www.barrgroup.com/embedded-systems/how-to/c-preprocessor-error-directive syntax of #error is very straightforward: #error
MySQL MariaDB PostgreSQL SQLite MS Office Excel Access Word Web Development HTML CSS Color Picker Languages C Language More ASCII Table Linux UNIX Java Clipart https://www.techonthenet.com/c_language/directives/error.php Techie Humor Advertisement C Language Introduction Compiling and Linking File Naming Preprocessor https://www-s.acm.illinois.edu/webmonkeys/book/c_guide/1.7.html Directives #include #define #undef #if #ifdef #ifndef #elif #else #endif #warning #error Comments Variables Integer Variables Float Variables First Program assert.h Functions ctype.h Functions locale.h Functions math.h Functions setjmp.h Functions signal.h Functions stdarg.h Functions stdio.h Functions stdlib.h Functions string.h Functions time.h Functions NEXT: Comments C Language: #error c #error Directive This C tutorial explains how to use the #error preprocessor directive in the C language. Description In the C Programming Language, the #error directive causes preprocessing to stop at the location where the directive is encountered. Information following the #error directive is output as a message prior to stopping preprocessing. Syntax The syntax for the directive #error c #error directive in the C language is: #error message message Message to output prior to stopping preprocessing. Example Let's look at how to use #error directives in your C program. The following example shows the output of the #error directive: /* Example using #error directive by TechOnTheNet.com */ #include
They must begin on a separate line. Syntax: #if constant_expression #else
#endif
or
#if constant_expression #elif constant_expression #endif The compiler only compiles the code after the #if expression if the constant_expression evaluates to a non-zero value (true). If the value is 0 (false), then the compiler skips the lines until the next #else, #elif, or #endif. If there is a matching #else, and the constant_expression evaluated to 0 (false), then the lines between the #else and the #endif are compiled. If there is a matching #elif, and the preceding #if evaluated to false, then the constant_expression after that is evaluated and the code between the #elif and the #endif is compiled only if this expression evaluates to a non-zero value (true). Examples: int main(void) { #if 1 printf("Yabba Dabba Do!\n"); #else printf("Zip-Bang!\n"); #endif return 0; }
Only "Yabba Dabba Do!" is printed. int main(void) { #if 1 printf("Checkpoint1\n"); #elif 1 printf("Checkpoint2\n"); #endif return 0; }
Only "Checkpoint1" is printed. Note that if the first line is #if 0, then only "Checkpoint2" would be printed. #if OS==1 printf("Version 1.0"); #elif OS==2 printf("Version 2.0"); #else printf("Version unknown"); #endif
Prints according to the setting of OS which is defined with a #define. 1.7.2 #define, #undef, #ifdef, #ifndef The preprocessing directives #define and #undef allow the definition of identifiers which hold a certain value. These identifiers can simply be constants or a macro function. The directives #ifdef and #ifndef allow conditional compiling of certain lines of code based on whether or not an identifier has been defined. Syntax: #define identifier replacement-code #undef identifier #ifdef identifier #else or #elif #endif #ifndef identifier #else or #elif #endif #ifdef identifier is the same is #if defined( identifier). #ifndef identifier is the same as #if !defined(identifier). An identifier defined with #define is available anywhere in the source code until a #undef is reached. A function macro can be defined with #define in the following manner: #define identifier(parameter-list) (replacement-text) The values in the parameter-list are replaced in the r