The body of a macro cannot contain preprocessor directives. Any time the compiler sees a # as the first non whitespace character it says - this is a preprocessor directive and not part of the macro body. Even if the # got bound up in the macro body text, it would not have a newline preceding it as the backslashes just "join" all the text together without any newlines in between, i.e. the compiler does not look for preprocessor directives when rescanning substituted text. Maybe you could encode __LINE__ instead of reporting it directly and also define a unique constant for each source file as well - instead of using the filename. Your method wouldn't provide uniqueness across multiple translation units anyway. Graeme
-----Original Message----- From: boost-bounces@lists.boost.org [mailto:boost-bounces@lists.boost.org] On Behalf Of Suman Cherukuri Sent: Tuesday, 30 August 2005 9:49 a.m. To: boost@lists.boost.org Subject: [boost] Preprocessot question
This probably doesn't belong to boost mailing list, but since boost has a lot of support in preprocessor, there may be someone who can answer my question.
I'm using general 'C' compiler in this project (hence I cannot use boost headers). I want to write a macro as follows;
#define ERR(x, y) \ { \ # ifndef ERR##x \ # define ERR##x \ # else \ # error ERR##x already defined\ # endif y = x; \ }
When I compile, I get the error saying, error C2162: expected macro formal parameter
on all the preprocessor lines inside the #define ERR(...) body.
The reason I want to do something like this is to have some unique numbers in the code (like locators. Don't want to use __FILE__ and __LINE__ for security reasons) and want to capture duplicates at compiletime.
For example if I say in the code, int err = 10000 in one file, I don't want any other engineer to use 10000 in the anywhere else in the code.
So I started writing something like int err = ERR(10000) but got into several compiler problems as I mentioned above.
Any suggeations?
Thanks,
--Suman
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