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#1 2010-08-28 15:14:33
- Berticus
- Member
- Registered: 2008-06-11
- Posts: 731
Beside preprocessor directives, what does # mean in C?
I'm looking through the FFmpeg source code, and here's an example of what they're doing:
#define REGISTER_MUXER(X,x) { \
extern AVOutputFormat x##_muxer; \
if(CONFIG_##X##_MUXER) av_register_output_format(&x##_muxer); }
#define REGISTER_DEMUXER(X,x) { \
extern AVInputFormat x##_demuxer; \
if(CONFIG_##X##_DEMUXER) av_register_input_format(&x##_demuxer); }
#define REGISTER_MUXDEMUX(X,x) REGISTER_MUXER(X,x); REGISTER_DEMUXER(X,x)
#define REGISTER_PROTOCOL(X,x) { \
extern URLProtocol x##_protocol; \
if(CONFIG_##X##_PROTOCOL) av_register_protocol2(&x##_protocol, sizeof(x##_protocol)); }x##_muxer, x##_demuxer, and x##_protocol don't look like they should be valid variable names. So why are they allowed here?
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#2 2010-08-28 15:39:04
- falconindy
- Developer
- From: New York, USA
- Registered: 2009-10-22
- Posts: 4,111
- Website
Re: Beside preprocessor directives, what does # mean in C?
It's valid preprocessor. the ## operator does concatenation.
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