I have #included in a file but get the following compile time error:

/tmp/ccXM0HkR.o: In function `boost::basic_regex >::assign(char const*, char const*, unsigned int)': contact.cpp:(.text._ZN5boost11basic_regexIcNS_12regex_traitsIcNS_16cpp_regex_traitsIcEEEEE6assignEPKcS7_j[boost::basic_regex >::assign(char const*, char const*, unsigned int)]+0x27): undefined reference to `boost::basic_regex

...

...

::do_assign(char const*, char const*, unsigned int)'

collect2: ld returned 1 exit status

This file definitely exists at /usr/include/boost/regex.hpp. Another Boost #include in the same file () produces no error. 'ldconfig -p' lists libboost_regex.so.

What am I doing wrong?

First off it's not a compile time error - it's a linker error - the linker is saying that some symbols used by your program can't be found. In short you need to add a reference to libboost_regex on the command line, something like: g++ myfile.cpp -lboost_regex HTH, John.