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I have got a series of errors I have added -l ssl and -l crypto. However I do not know which version library I need to install 

/usr/include/boost/asio/ssl/detail/openssl_init.hpp:48: undefined reference to `SSL_library_init'
/usr/include/boost/asio/ssl/detail/openssl_init.hpp:49: undefined reference to `SSL_load_error_strings'
/usr/include/boost/asio/ssl/detail/openssl_init.hpp:50: undefined reference to `SSL_library_init'
/usr/include/boost/asio/ssl/detail/openssl_init.hpp:52: undefined reference to `CRYPTO_num_locks'
/usr/include/boost/asio/ssl/detail/openssl_init.hpp:55: undefined reference to `CRYPTO_set_locking_callback'
/usr/include/boost/asio/ssl/detail/openssl_init.hpp:56: undefined reference to `CRYPTO_set_id_callback'
/usr/include/boost/asio/ssl/detail/openssl_init.hpp:48: undefined reference to `SSL_library_init'
/usr/include/boost/asio/ssl/detail/openssl_init.hpp:49: undefined reference to `SSL_load_error_strings'

There are numerous options such as 

Note, selecting 'libss7-dbg' for regex 'libssl*'
Note, selecting 'libssl0.9.8-dbg' for regex 'libssl*'
Note, selecting 'libss7-dev' for regex 'libssl*'
Note, selecting 'libssl0.9.8' for regex 'libssl*'
Note, selecting 'libss2' for regex 'libssl*'
Note, selecting 'libssm-dev' for regex 'libssl*'
Note, selecting 'libssl' for regex 'libssl*'
Note, selecting 'libssh-4' for regex 'libssl*'
Note, selecting 'libssh-2-dev' for regex 'libssl*'
Note, selecting 'libssh-2-doc' for regex 'libssl*'
Note, selecting 'libssl1.0.0' for regex 'libssl*'
Note, selecting 'libsscm3' for regex 'libssl*'
Note, selecting 'libssl-ocaml-dev' instead of 'libssl-ocaml-dev-l8h98'
Note, selecting 'libssl-ocaml' instead of 'libssl-ocaml-l8h98'
Note, selecting 'libssreflect-ocaml' instead of 'libssreflect-ocaml-kevs8'
Note, selecting 'libssreflect-ocaml-dev' instead of 'libssreflect-ocaml-dev-kevs8'
Note, selecting 'python-libssh2' instead of 'python2.7-libssh2'
libss2 is already the newest version.

and 

Note, selecting 'libcryptokit-ocaml' for regex 'libcrypto*'
Note, selecting 'libcryptokit-ocaml-02n31' for regex 'libcrypto*'
Note, selecting 'libcryptgps-ocaml-dev' for regex 'libcrypto*'
Note, selecting 'libcrypt-blowfish-perl' for regex 'libcrypto*'
Note, selecting 'libcrypt-saltedhash-perl' for regex 'libcrypto*'
Note, selecting 'libcrypt-gcrypt-perl' for regex 'libcrypto*'
Note, selecting 'libcryptui' for regex 'libcrypto*'
Note, selecting 'libcrypt-generatepassword-perl' for regex 'libcrypto*'
Note, selecting 'libcrypt-dh-gmp-perl' for regex 'libcrypto*'
Note, selecting 'libcrypt-cbc-perl' for regex 'libcrypto*'
Note, selecting 'libcrypt-dsa-perl' for regex 'libcrypto*'
Note, selecting 'libcrypt-dh-perl' for regex 'libcrypto*'
Note, selecting 'libcrypt-openssl-bignum-perl' for regex 'libcrypto*'
Note, selecting 'libcryptgps-ocaml-dev' instead of 'libcryptgps-ocaml-dev-1zmb9'
Note, selecting 'libcryptokit-ocaml' instead of 'libcryptokit-ocaml-02n31'
Note, selecting 'libcryptokit-ocaml-dev' instead of 'libcryptokit-ocaml-dev-02n31'

g++ -pthread -l ssl -lcrypto IpcManagerMain.cpp -o IpcManagerMain.o  -lentity++ -lpersistence++ -lplatform++ -lreflection++ -lmonitor++ -lmeta++ -lipc++ -lbroadcast++ -lutilities++ -L/usr/lib          -lboost_serialization -lboost_thread-mt -lboost_date_time -lboost_iostreams -lboost_program_options -lboost_filesystem -lboost_system

There are more but I have shortened it. Could someone please point me in the right direction?

gda2004
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    Please add the **exact** compiler call to your question. – Zeta Nov 29 '12 at 12:29
  • I have found out that it is the order that I have put the flags in the -l ssl etc should be at the end thanks for your help :) – gda2004 Nov 29 '12 at 13:18
  • possible duplicate of [Noobish, linker errors when compiling against glib...?](http://stackoverflow.com/questions/9966959/noobish-linker-errors-when-compiling-against-glib) – hmjd Nov 29 '12 at 13:20

1 Answers1

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Imagine the (imaginary) linker trying to link these modules:

link moda modb modc modd

The linker doesn't (for efficiency reasons) record all the symbols it has seen in moda to try to match them with symbols in modb. For example, if moda is a huge library, then the linking process becomes very slow (and memory consuming), if all symbols of moda are remembered throughout the whole process.

As a result, the linker always remembers only the (so far) missing symbols and tries to find them in the modules that come afterwards. Note that this is only true for libraries. This is because objects of the same library/application may have circular dependency.

This means that missing symbols of modb for example, are searched for only in modc and modd and not in moda (again, if moda, modc and modd are libraries).

Therefore, if you have modx using symbols of mody, then you must mention mody after modx in the link command.

For example, if you have files main.o, funcs.o and libmatrix.a, then you need to write your link command like this:

gcc funcs.o main.o -lmatrix

otherwise, if you write gcc -lmatrix funcs.o main.o, the symbols of libmatrix.a will not be visible to funcs.o and main.o.

Shahbaz
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