Undefined References

[Former user]

Hi,

I'm trying to compile Write-Example.cpp but it fails with the following error messages.

$ g++ main.cpp 
/usr/bin/ld: /tmp/cce50VeC.o: in function `main':
main.cpp:(.text+0x61): undefined reference to `Vector::BLF::File::File()'
/usr/bin/ld: main.cpp:(.text+0x86): undefined reference to `Vector::BLF::File::open(char const*, std::_Ios_Openmode)'
/usr/bin/ld: main.cpp:(.text+0x95): undefined reference to `Vector::BLF::File::is_open() const'
/usr/bin/ld: main.cpp:(.text+0xe3): undefined reference to `Vector::BLF::CanMessage::CanMessage()'
/usr/bin/ld: main.cpp:(.text+0x152): undefined reference to `Vector::BLF::File::write(Vector::BLF::ObjectHeaderBase*)'
/usr/bin/ld: main.cpp:(.text+0x161): undefined reference to `Vector::BLF::File::close()'
/usr/bin/ld: main.cpp:(.text+0x175): undefined reference to `Vector::BLF::File::~File()'
/usr/bin/ld: main.cpp:(.text+0x1a0): undefined reference to `Vector::BLF::File::~File()'
collect2: error: ld returned 1 exit status

I'm using gcc (Debian 8.3.0-6) 8.3.0 and cmake version 3.13.4

The output of uname -a is Linux mx 4.19.0-6-amd64 #1 SMP Debian 4.19.67-2+deb10u2 (2019-11-11) x86_64 GNU/Linux

Any idea what's going wrong?

Regards, Soeren

[Tobias Lorenz]

Hi Soeren,

yes, sure. Calling “g++ main.cpp” will build the main.o and try to link it to an executable. But as you gave no instructions to what to link too and also haven’t compiled all the other files, this is not gonna work.

Can you try to follow the instructions in README.md, so ideally using cmake to compile everything? cmake will run the compiler/linker commands in the appropriate order.

Bye

Tobias

[Søren Bruhn Ebbesen]

Hi Tobias,

Thanks for you quick reply. I think my original post was a bit misleading due to a typo. I meant that I’m trying to compile using ‘''g++ Write-Example.cpp’'' (not main.cpp). Regarding the installation of Vector_BLF, I followed the instructions in README.md i.e. cmake, make, make install, etc.

Do I need to link to Vector_BLF when I compile Write-Example.cpp e.g. g++ -lVector_BLF or anything like that?

Apologies for the trivial questions. I am new to this stuff…

Thanks,

Soeren

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[Søren Bruhn Ebbesen]

So I just tried my own idea of compiling with

g++ -lVector_BLF Write-Example.cpp

So the compilation appears to finish without errors, but when I run the resulting executable (./a.out), I get the following error

./a.out: error while loading shared libraries: libVector_BLF.so.2: cannot open shared object file: No such file or directory

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[Søren Bruhn Ebbesen]

Me again…

So everything seems to work now after running.

ldconfig

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[Tobias Lorenz]

That’s great to hear. Then you found the solution, faster than me

Bye

Tobias

[Tobias Lorenz]

Linker issue solved.