A simple coding blog for new graduates

This week I’ve re-acquainted myself with Linux at work in order to port an app from Windows to Linux. Besides the aggravation of setting up the OS, IDE, and workflow, I had to use a 3rd party library called Crypto++. Well, it wasn’t obvious to set up or figure out so I’d put this out there in case someone has the same problem.

Basically I was able to include the files, but I got a linker error despite including the files in the project file in Qt. This is the error:

g++ -o encrypter -L/usr/lib -Lcryptopp -lcrypto++ -lQtGui -lQtCore -lpthread
encrypter.o: In function `CryptoPP::AllocatorWithCleanup::allocate(unsigned int, void const*)':
encrypter.cpp:(.text._ZN8CryptoPP20AllocatorWithCleanupIhLb1EE8allocateEjPKv[CryptoPP::AllocatorWithCleanup::allocate(unsigned int, void const*)]+0x2b): undefined reference to `CryptoPP::AlignedAllocate(unsigned int)'
encrypter.cpp:(.text._ZN8CryptoPP20AllocatorWithCleanupIhLb1EE8allocateEjPKv[CryptoPP::AllocatorWithCleanup::allocate(unsigned int, void const*)]+0x38): undefined reference to `CryptoPP::UnalignedAllocate(unsigned int)'
encrypter.o: In function `CryptoPP::AllocatorWithCleanup::deallocate(void*, unsigned int)':
encrypter.cpp:(.text._ZN8CryptoPP20AllocatorWithCleanupIhLb1EE10deallocateEPvj[CryptoPP::AllocatorWithCleanup::deallocate(void*, unsigned int)]+0x25): undefined reference to `CryptoPP::AlignedDeallocate(void*)'
encrypter.cpp:(.text._ZN8CryptoPP20AllocatorWithCleanupIhLb1EE10deallocateEPvj[CryptoPP::AllocatorWithCleanup::deallocate(void*, unsigned int)]+0x32): undefined reference to `CryptoPP::UnalignedDeallocate(void*)'
collect2: ld returned 1 exit status
make: Leaving directory `/home/alex/projects/encrypter'
make: *** [encrypter] Error 1
Exited with code 2.
Error while building project encrypter
When executing build step 'Make'

The proper way to include crypto++ is NOT to download it from the website. Use terminal to get the library:

sudo apt-get install libcrypto++8 libcrypto++8-dbg libcrypto++-dev

Then check if installed on system:

apt-cache pkgnames | grep -i crypto++

Which should result with:

libcrypto++-utils
libcrypto++8
libcrypto++8-dbg
libcrypto++-dev
libcrypto++-doc

If the information above is different (which is possible if it becomes out of date), check the Crypto++ Linux wiki for instructions.

Now add the library to project with the following linkage (written as a makefile macro, but just put the -L and -I parts in the command line if you’re compiling manually):

LIBS += -L/usr/lib/crypto++ -lcrypto++
INCS += -I/usr/include/crypto++

While is is rather specific, someone out there is probably searching for this so here ya go!