c++ - 使用静态库时未定义的函数引用

Question

我正在尝试使用遗传算法编写程序，这是一种特殊类型的优化算法。我为此任务找到了一个名为“Evolutionary Objects”的免费库，并实现了一个非常简单的遗传算法实例。程序代码、netbeans 实现的构建命令以及最后我收到的错误消息都在下面单独的 block 中发布。如果您允许我提供帮助，您会发现 cout 函数出了问题。当我在互联网上搜索类似的困难时，我发现人们一直在通过简单地使用 g++ 而不是 gcc 来纠正问题，但我已经在使用 g++，如您所见。任何帮助将不胜感激....

程序代码如下:

#include <stdexcept>
#include <iostream>
#include <eo>
#include <ga.h>

typedef eoBit<double> Indi;

double binary_value(const Indi & _indi)
{
  double sum = 0;
  for (unsigned i = 0; i < _indi.size(); i++)
    sum += _indi[i];
  return sum;
}

void main_function(int argc, char **argv)
{

  const unsigned int SEED = 42;      // seed for random number generator
  const unsigned int T_SIZE = 3;     // size for tournament selection
  const unsigned int VEC_SIZE = 16;   // Number of bits in genotypes
  const unsigned int POP_SIZE = 100;  // Size of population
  const unsigned int MAX_GEN = 400;  // Maximum number of generation before STOP
  const float CROSS_RATE = 0.8;      // Crossover rate
  const double P_MUT_PER_BIT = 0.01; // probability of bit-flip mutation
  const float MUT_RATE = 1.0;        // mutation rate

  rng.reseed(SEED);

  eoEvalFuncPtr<Indi> eval(  binary_value );

  eoPop<Indi> pop;

  for (unsigned int igeno=0; igeno<POP_SIZE; igeno++)
    {
      Indi v;           // void individual, to be filled
      for (unsigned ivar=0; ivar<VEC_SIZE; ivar++)
    {
      bool r = rng.flip(); // new value, random in {0,1}
      v.push_back(r);      // append that random value to v
    }
      eval(v);                 // evaluate it
      pop.push_back(v);        // and put it in the population
    }

  pop.sort();

  cout << "Initial Population" << endl;
  cout << pop;

  eoDetTournamentSelect<Indi> select(T_SIZE);  // T_SIZE in [2,POP_SIZE]
  eo1PtBitXover<Indi> xover;
  eoBitMutation<Indi>  mutation(P_MUT_PER_BIT);

  eoGenContinue<Indi> continuator(MAX_GEN);

  eoSGA<Indi> gga(select, xover, CROSS_RATE, mutation, MUT_RATE, eval, continuator);

  gga(pop);

  pop.sort();
  cout << "FINAL Population\n" << pop << endl;
}

int main(int argc, char **argv)
{
main_function(argc, argv);
    return 1;
}
}

Netbeans 向我展示了它在尝试构建时这样做:

make[1]: Entering directory `/home/gregemerson/EO_GA/EO_GA'
rm -f -r build/Debug
rm -f dist/Debug/GNU-Linux-x86/eo_ga
make[1]: Leaving directory `/home/gregemerson/EO_GA/EO_GA'


CLEAN SUCCESSFUL (total time: 94ms)

"/usr/bin/make" -f nbproject/Makefile-Debug.mk QMAKE= SUBPROJECTS= .build-conf
make[1]: Entering directory `/home/gregemerson/EO_GA/EO_GA'
"/usr/bin/make"  -f nbproject/Makefile-Debug.mk dist/Debug/GNU-Linux-x86/eo_ga
make[2]: Entering directory `/home/gregemerson/EO_GA/EO_GA'
mkdir -p build/Debug/GNU-Linux-x86
rm -f build/Debug/GNU-Linux-x86/main.o.d
g++    -c -g -I../../EO/EO/eo/src -MMD -MP -MF build/Debug/GNU-Linux-x86/main.o.d -o build/Debug/GNU-Linux-x86/main.o main.cpp
mkdir -p dist/Debug/GNU-Linux-x86
g++     -o dist/Debug/GNU-Linux-x86/eo_ga build/Debug/GNU-Linux-x86/main.o -L../../EO/EO/eo/build/lib /home/gregemerson/EO/EO/eo/build/lib/libcma.a /home/gregemerson/EO/EO/eo/build/lib/libeoutils.a /home/gregemerson/EO/EO/eo/build/lib/libes.a /home/gregemerson/EO/EO/eo/build/lib/libga.a 

错误信息如下:

/home/gregemerson/EO_GA/EO_GA/main.cpp:94: undefined reference to `operator<<(std::basic_ostream<char, std::char_traits<char> >&, eoPrintable const&)'
/home/gregemerson/EO_GA/EO_GA/main.cpp:99: undefined reference to `operator<<(std::basic_ostream<char, std::char_traits<char> >&, eoPrintable const&)'
/home/gregemerson/EO_GA/EO_GA/main.cpp:149: undefined reference to `operator<<(std::basic_ostream<char, std::char_traits<char> >&, eoPrintable const&)'
build/Debug/GNU-Linux-x86/main.o: In function `eoPop<eoBit<double> >::sortedPrintOn(std::basic_ostream<char, std::char_traits<char> >&) const':
/home/gregemerson/EO_GA/EO_GA/../../EO/EO/eo/src/eoPop.h:294: undefined reference to `operator<<(std::basic_ostream<char, std::char_traits<char> >&, eoPrintable const&)'
build/Debug/GNU-Linux-x86/main.o: In function `std::ostream_iterator<eoBit<double>, char, std::char_traits<char> >::operator=(eoBit<double> const&)':
/usr/include/c++/4.6/bits/stream_iterator.h:198: undefined reference to `operator<<(std::basic_ostream<char, std::char_traits<char> >&, eoPrintable const&)'
collect2: ld returned 1 exit status
make[2]: *** [dist/Debug/GNU-Linux-x86/eo_ga] Error 1
make[2]: Leaving directory `/home/gregemerson/EO_GA/EO_GA'
make[1]: *** [.build-conf] Error 2
make[1]: Leaving directory `/home/gregemerson/EO_GA/EO_GA'
make: *** [.build-impl] Error 2

您的回答确实正确解决了我的 cout(pop) 问题。但是，我现在在我正在使用的静态库之一的 header 中看到类似的错误，以及看起来与基本 c++ 库之一相关的内容。我得到以下信息。这对您来说有意义吗？

build/Debug/GNU-Linux-x86/main.o: In function `std::ostream_iterator<eoBit<double>, char, std::char_traits<char> >::operator=(eoBit<double> const&)':
/usr/include/c++/4.6/bits/stream_iterator.h:198: undefined reference to `operator<<(std::basic_ostream<char, std::char_traits<char> >&, eoPrintable const&)'
build/Debug/GNU-Linux-x86/main.o: In function `eoPop<eoBit<double> >::sortedPrintOn(std::basic_ostream<char, std::char_traits<char> >&) const':
/home/gregemerson/EO_GA/EO_GA/../../EO/EO/eo/src/eoPop.h:294: undefined reference to `operator<<(std::basic_ostream<char, std::char_traits<char> >&, eoPrintable const&)'

Answer 1

问题(例如)在这里:

cout << pop;

错误，

/home/gregemerson/EO_GA/EO_GA/main.cpp:94: undefined reference to 
`operator<<(std::basic_ostream<char, std::char_traits<char> >&, eoPrintable const&)'

意味着没有基本函数知道如何将 eoPrintable 对象推送到 ostream 中。

基于link在注释中提供，这个 eoPop 类定义了一些打印方法:sortedPrintOn和 printOn .

为了使用其中之一打印到 cout，您需要执行以下操作:

pop.printOn(cout); //or pop.printOn(std::cout) if you remove using namespace std;
pop.printSortedOn(cout);