Editing STIR FAQ (section)

== Problems with linking ==
These errors occur after a long time in the building process as all "object files" will be compiled first, before
the executables will be build by linking the object files and the libraries. Errors would say something like a missing library.

You probably miss some development libraries. See the installation guide.

=== Problems with ecat library ===
Including the ecat library on some Linux distributions leads to linking errors as such: 

<pre>
/opt/ecat/libecat.a(rts_cmd.o): In function `initAcqTcpClient': rts_cmd.c:(.text+0x9c): 
undefined reference to `clnttcp_create'
rts_cmd.c:(.text+0xd2): undefined reference to `clnt_pcreateerror'
/opt/ecat/libecat.a(rts_cmd.o): In function `doAcsAcqCommand':rts_cmd.c:(.text+0x16b): undefined reference to `clnt_perror'
/opt/ecat/libecat.a(rts_cmd.o): In function `rts_rmhd':rts_cmd.c:(.text+0x1ad): undefined reference to `xdr_wrapstring'
/opt/ecat/libecat.a(rts_cmd.o): In function `rts_wmhd':rts_cmd.c:(.text+0x264): undefined reference to `xdr_int'
/opt/ecat/libecat.a(rts_cmd.o): In function `rts_wshd':rts_cmd.c:(.text+0x3c8): undefined reference to `xdr_int'
/opt/ecat/libecat.a(rts_cmd.o): In function `rts_wdat':rts_cmd.c:(.text+0x4e1): undefined reference to `xdr_int'
rts_cmd.c:(.text+0x512): undefined reference to `cfree'
/opt/ecat/libecat.a(rts_cmd.o): In function `rtsWblk': rts_cmd.c:(.text+0x650): undefined reference to `xdr_int'
/opt/ecat/libecat.a(matrix_xdr.o): In function `xdr_MATRIX_FUNCTIONS': matrix_xdr.c:(.text+0x5): undefined reference to `xdr_enum'
/opt/ecat/libecat.a(matrix_xdr.o): In function `xdr_XMAIN_HEAD': matrix_xdr.c:(.text+0x28): undefined reference to `xdr_opaque'
matrix_xdr.c:(.text+0x44): undefined reference to `xdr_opaque'
matrix_xdr.c:(.text+0x54): undefined reference to `xdr_short'
matrix_xdr.c:(.text+0x64): undefined reference to `xdr_short'
matrix_xdr.c:(.text+0x74): undefined reference to `xdr_short'
</pre>

This can be fixed in two ways. Either remove rts support from ecat (recommended) or link STIR to libtirts.so (installed independently on your system). 

* For the first option one would have to apply the [https://github.com/NikEfth/ecat_patch_STIR_LLN_support patch] on the ecat directory (before compilation), by following this procedure: 

# Move the patch file to the directory of the original folder
# This folder will get modified, so make a backup of it somewhere
# Run:
<pre>
    patch -s -p0 < stir_ecat_no_rts_no_xdr.patch
</pre>

At this point, the original folder contains the modified content.

* The second option is achieved by applying the following modification at buildblock/CMakeLists.txt or IO/CMakeLists.txt (one would be enough): 

<pre>
if (LLN_FOUND)
  target_link_libraries(buildblock ${LLN_LIBRARIES} -ltirpc)
endif()
</pre>