Can I use an ifdef in a #define line ...

.NET C C++ CSS DBA General HTML Java JavaScript JSP JUnit MySQL Networking Oracle Perl Perl PHP PL/SQL RSS Software QA SQL Server Struts Unix Windows XHTML XML

Home Hot About Collections Index RSS Atom Ask

Tester Developer DBA Windows JAR DLL Files Certificates RegEx Links Q&A Biotech Phones Travel FAQ Forum

Home > C

Can I use an #ifdef in a #define line, to define something two different ways, like this?
#define a b \
#ifdef whatever
c d
#else
e f g
#endif

✍: Guest

No. You can't ``run the preprocessor on itself,'' so to speak. What you can do is use one of two completely separate #define lines, depending on the #ifdef setting:

#ifdef whatever
#define a b c d
#else
#define a b e f g
#endif

2016-02-03, 1708👍, 0💬

How can I use a preprocessorif expression to ? ....
How can I use a preprocessor #if expression to tell whether a machine's byte order is big-endian or little-endian? You probably can't. The usual techniques for detecting endianness involve pointers or arrays of char, or maybe unions, but preprocessor arithmetic uses only long integers, and there is ... 2016-02-01, 1748👍, 0💬

Does the sizeof operator work in preprocessor if directives?
Does the sizeof operator work in preprocessor if directives? No. Preprocessing happens during an earlier phase of compilation, before type names have been parsed. Instead of sizeof, consider using the predefined constants in ANSI's <limits.h>, if applicable, or perhaps a ``configure'' script.... 2016-02-03, 1731👍, 0💬

I am using header files which accompany two different third-party libraries...
I'm using header files which accompany two different third-party libraries, and they are ``helpfully'' defining common macros such as TRUE, FALSE, Min(), and Max(), but the definitions clash with each other and with definitions I'd already established in my own header files. What can I do? This is i... 2016-02-10, 1730👍, 0💬

Can I use an ifdef in a #define line ...
Can I use an #ifdef in a #define line, to define something two different ways, like this? #define a b \ #ifdef whatever c d #else e f g #endif No. You can't ``run the preprocessor on itself,'' so to speak. What you can do is use one of two completely separate #define lines, depending on the #ifdef s... 2016-02-03, 1709👍, 0💬

I mm compiling a program, and I seem to be missing one of the header files it requires
I mm compiling a program, and I seem to be missing one of the header files it requires There are several situations, depending on what sort of header file it is that's ``missing''. If the missing header file is truly a standard one (that is, one defined by the ANSI C Standard, such as <stdio.... 2016-02-05, 1680👍, 0💬

Is there anything like an ifdef for typedefs?
Is there anything like an ifdef for typedefs? Unfortunately, no. (There can't be, because types and typedefs haven't been parsed at preprocessing time.) You may have to keep sets of preprocessor macros (e.g. MY_TYPE_DEFINED) recording whether certain typedefs have been declared. 2016-02-01, 1671👍, 0💬

How can I list all of the predefined identifiers?
How can I list all of the predefined identifiers? There's no standard way, although it is a common need. gcc provides a -dM option which works with -E, and other compilers may provide something similar. If the compiler documentation is unhelpful, the most expedient way is probably to extract printab... 2016-01-27, 1661👍, 0💬

I am including the right header file for the library function I am using, but the linker keeps saying its undefined.
I am including the right header file for the library function I am using, but the linker keeps saying its undefined. In the general case of calling code in an external library, using #include to pull in the right header file(s) is only half of the story; you also have to tell the linker to search th... 2016-02-10, 1660👍, 0💬

I inherited some code which contains far too many ...
I inherited some code which contains far too many #ifdef's for my taste. How can I preprocess the code to leave only one conditional compilation set, without running it through the preprocessor and expanding all of the #include's and #define's as well? There are programs floating around called unifd... 2016-01-29, 1615👍, 0💬

.NET C C++ CSS DBA General HTML Java JavaScript JSP JUnit MySQL Networking Oracle Perl Perl PHP PL/SQL RSS Software QA SQL Server Struts Unix Windows XHTML XML

Home Hot About Collections Index RSS Atom Ask

Tester Developer DBA Windows JAR DLL Files Certificates RegEx Links Q&A Biotech Phones Travel FAQ Forum

All rights in the contents of this web site are reserved by the individual author. fyicenter.com does not guarantee the truthfulness, accuracy, or reliability of any contents.