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I am attempting to use the libtommath library. I'm using the NetBeans IDE for my project on Ubuntu linux. I have downloaded and built the library, I have done a 'make install' to put the resulting .a file into /usr/lib/ and the .h files into /usr/include
It appears to be finding the files appropriately (since I no longer get those errors, which I did before installing into the /usr directories).
However, when I create a simple main making a call to mp_init (which is in the library), I get the following error when I attempt to make my project:
mkdir -p build/Debug/GNU-Linux-x86 rm -f build/Debug/GNU-Linux-x86/main.o.d gcc -c -g -MMD -MP -MF build/Debug/GNU-Linux-x86/main.o.d -o build/Debug/GNU-Linux-x86/main.o main.c mkdir -p dist/Debug/GNU-Linux-x86 gcc -o dist/Debug/GNU-Linux-x86/cproj1 build/Debug/GNU-Linux-x86/main.o build/Debug/GNU-Linux-x86/main.o: In function 'main': /home/[[myusername]]/NetBeansProjects/CProj1/main.c:18: undefined reference to `mp_init' collect2: ld returned 1 exit status make[2]: *** [dist/Debug/GNU-Linux-x86/cproj1] Error 1 So, it looks like the linker can't find the function within the library, however it IS there, so I just don't know what could be causing this.
I get the same error if I type the gcc command directly and skip the makefile, I also made sure the static library got compiled with gcc as well.
Edited to Add:
I get these same errors if I do the compile directly and add the library with -l or -L:
$ gcc -l /usr/lib/libtommath.a main.c /usr/bin/ld: cannot find -l/usr/lib/libtommath.a collect2: ld returned 1 exit status $ gcc -llibtommath.a main.c /usr/bin/ld: cannot find -llibtommath.a collect2: ld returned 1 exit status $ gcc -Llibtommath.a main.c /tmp/ccOxzclw.o: In function `main': main.c:(.text+0x18): undefined reference to `mp_init' collect2: ld returned 1 exit status $ gcc -Llibtommath.a main.c /tmp/ccOxzclw.o: In function `main': main.c:(.text+0x18): undefined reference to `mp_init' collect2: ld returned 1 exit status I am very rusty on this stuff, so I'm not sure I'm using the right command here, in the -L examples are the libraries being found? If the library isn't being found how on earth do I get it to find the library? It's in /usr/lib, I've tried it with the .a file in the current directory, etc. Is there an environment variable I need to set? If so, how, etc.
I've tried a completely different library (GMP) and had the EXACT same problem. This has got to be some kind of Ubuntu environment issue? Anyone have any idea how to fix this?
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So when we try to assign it a value in the main function, the linker doesn't find the symbol and may result in an “unresolved external symbol” or “undefined reference”. The way to fix this error is to explicitly scope the variable using '::' outside the main before using it.
You can fix undefined reference in C++ by investigating the linker error messages and then providing the missing definition for the given symbols. Note that not all linker errors are undefined references, and the same programmer error does not cause all undefined reference errors.
Undefined reference to main() means that your program lacks a main() function, which is mandatory for all C++ programs.
A symbol remains undefined when a symbol reference in a relocatable object is never matched to a symbol definition. Similarly, if a shared object is used to create a dynamic executable and leaves an unresolved symbol definition, an undefined symbol error results.
The trick here is to put the library AFTER the module you are compiling. The problem is a reference thing. The linker resolves references in order, so when the library is BEFORE the module being compiled, the linker gets confused and does not think that any of the functions in the library are needed. By putting the library AFTER the module, the references to the library in the module are resolved by the linker.
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Yes, It is required to add libraries after the source files/objects files. This command will solve the problem:
gcc -static -L/usr/lib -I/usr/lib main.c -ltommath If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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