CODEWITHSUNDEEP
c++dynamic-linkingdynamic-library
UserX
UserX

Reputation: 187

Why is my main not finding the functions from my shared library?

I have 4 separate functions in 4 different files. The functions look like this:

SieveOfEratosthenes.cpp

bool SieveOfEratosthenes(int n) {
//
}

They all have no includes. In my main.cpp program I have

//Includes
void compare(bool (*f)(int)) {
//
}

int main(int argc, char **argv) {
  compare(isPrimeAKS);
  compare(isPrimeModulo);
  compare(isPrimeSQRT);
  compare(SieveOfEratosthenes);
  return 0;
}

This is my makefile:

all: main clean

main: main.cpp lib.so
    g++ -o main main.cpp -L.

lib.so: EratosthenesSieve.o AKS.o ModuloAlg.o SQRTModuloAlg.o
    g++ -shared -o lib.so AKS.o ModuloAlg.o SQRTModuloAlg.o EratosthenesSieve.o

EratosthenesSieve.o: EratosthenesSieve.cpp
    g++ -c -Wall -fpic EratosthenesSieve.cpp

AKS.o: AKS.cpp
    g++ -c -Wall -fpic AKS.cpp

ModuloAlg.o: ModuloAlg.cpp
    g++ -c -Wall -fpic ModuloAlg.cpp

SQRTModuloAlg.o: ModuloAlg.cpp
    g++ -c -Wall -fpic SQRTModuloAlg.cpp

clean:
    rm -f *.o

Compiling errors at main(after building the shared library lib.so) with errors like:

‘isPrimeAKS’ was not declared in this scope.

I don't understand why, since they all are in the library provided to the compiler.

EDIT if you have the same problem: After declaring in a header the problem becomes

undefined reference to `isPrimeAKS(int)' see the accepted answer why.

Upvotes: 1

Views: 1245

Answers (1)

Jérôme Richard
Jérôme Richard

Reputation: 50328

Firstly, the prototype of the function isPrimeAKS must be declared in the headers included in main.cpp or in the beginning of main.cpp (at least before it is called).

Secondly, you should link the dynamic library at compile time or load it at runtime. Indeed, g++ -o main main.cpp -L. do not link lib.so. You need to add the -lyourlib option. However, since this option ignore the prefix lib and the suffix .so, you need to change the invalid name of lib.so to something valid like libaks.so and then link it with g++ -o main main.cpp -L. -laks.

Upvotes: 6

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