test.c...
#include <termios.h>
#include <stdio.h>
int main() {
printf("%x\n",B600);
}
On my system this prints "8".
gcc -M test.c shows
/usr/include/stdc-predef.h /usr/include/termios.h \
/usr/include/features.h /usr/include/x86_64-linux-gnu/sys/cdefs.h \
/usr/include/x86_64-linux-gnu/bits/wordsize.h \
/usr/include/x86_64-linux-gnu/gnu/stubs.h \
/usr/include/x86_64-linux-gnu/gnu/stubs-64.h \
/usr/include/x86_64-linux-gnu/bits/types.h \
/usr/include/x86_64-linux-gnu/bits/typesizes.h \
/usr/include/x86_64-linux-gnu/bits/termios.h \
/usr/include/x86_64-linux-gnu/sys/ttydefaults.h /usr/include/stdio.h \
/usr/lib/gcc/x86_64-linux-gnu/4.9/include/stddef.h /usr/include/libio.h \
/usr/include/_G_config.h /usr/include/wchar.h \
/usr/lib/gcc/x86_64-linux-gnu/4.9/include/stdarg.h \
/usr/include/x86_64-linux-gnu/bits/stdio_lim.h \
/usr/include/x86_64-linux-gnu/bits/sys_errlist.h
Inside of /usr/include/x86_64-linux-gnu/bits/termios.h:
#define B600 0000010
None of the other headers have a define for B600. Where is the value of 8 coming from?
In C, a number literal starting with a zero is interpreted as an octal number, so 010 means 10 in octal, and therefore 8.