未定义符号：vtable

Question

这是一个编译器错误，我无法确定问题的来源。

这是类LocalQualityMeasure的头文件。

#include <unordered_set>

#include "../clustering/Clustering.h"
#include "../graph/Graph.h"

namespace Project {

/**
 * Abstract base class for all local clustering quality measures.
 */
class LocalQualityMeasure {


public:

    LocalQualityMeasure();

    virtual ~LocalQualityMeasure();

    virtual double getQuality(std::unordered_set<node>& C, Graph& G) = 0;
};

} /* namespace Project */

并且源代码：

#include "LocalQualityMeasure.h"

namespace Project {

LocalQualityMeasure::LocalQualityMeasure() {
}

LocalQualityMeasure::~LocalQualityMeasure() {
    // TODO Auto-generated destructor stub
}


} /* namespace Project */

这是一个派生类Conductance，头文件。

#include <algorithm>

#include "LocalQualityMeasure.h"

namespace Project {

class Conductance: public Project::LocalQualityMeasure {
public:
    Conductance();
    virtual ~Conductance();

    virtual double getQuality(std::unordered_set<node>& C, Graph& G);
};

} /* namespace Project */

和源代码

#include "Conductance.h"

namespace Project {

Conductance::Conductance() : LocalQualityMeasure() {
}

Conductance::~Conductance() {
    // TODO Auto-generated destructor stub
}

double getQuality(std::unordered_set<node>& C, Graph& G) {

    double volume = 0;
    double boundary = 0;
    double all = 0;

    for (auto it = C.begin(); it != C.end(); ++it) {
        volume = volume + G.degree(*it);
        G.forNeighborsOf(*it, [&](node v){
            if (C.find(v) == C.end()) boundary++;
        });
    }

    G.forNodes([&](node v){
        all = all + G.degree(v);
    });

    if (volume == 0 || all-volume == 0)
        return 1;
    return boundary / std::min(volume, all-volume);
}

} /* namespace Project */

连接器报告缺少虚函数表的错误：

Undefined symbols for architecture x86_64:
  "Project::Conductance::getQuality(std::unordered_set<long long, std::hash<long long>, std::equal_to<long long>, std::allocator<long long> >&, Project::Graph&)", referenced from:
      vtable for Project::Conductance in Conductance.o
ld: symbol(s) not found for architecture x86_64
collect2: error: ld returned 1 exit status
make: *** [Project-CommunityDetection-DPar] Error 1

我使用带有--std=c++11的GCC 4.7。

- clstaudt

---

如果我没记错的话，当一个类声明了虚函数但没有实现时，我在使用gcc编译时会收到这些误导性的消息。它并没有指出缺失的函数，而是说缺少vtable。 - Balog Pal

Answer 1

你在实现 getQuality 方法时忘记了类作用域：

double Conductance::getQuality(std::unordered_set<node>& C, Graph& G) 
{
  .....
}

- juanchopanza

---

谢谢，我刚才没看到。 - clstaudt

Answer 2

您需要在实现文件中添加类作用域：

double Conductance::getQuality(std::unordered_set<node>& C, Graph& G) {...

否则，链接器将无法找到在头文件中定义的方法的实现。

- tune2fs