使用模板化接口会导致“未定义引用”

Posted 2021-05-04

所以我得到以下编译错误：

CMakeFiles/moje.dir/src/main/cpp/main.cpp.o:(.rodata._ZTV10ReadWriterINSt7__cxx1119basic_ostringstreamIcSt11char_traitsIcESaIcEEENS0_19basic_istringstreamIcS3_S4_EEE[_ZTV10ReadWriterINSt7__cxx1119basic_ostringstreamIcSt11char_traitsIcESaIcEEENS0_19basic_istringstreamIcS3_S4_EEE]+0x48): undefined reference to `Writer<std::__cxx11::basic_istringstream<char, std::char_traits<char>, std::allocator<char> > >::write(std::__cxx11::basic_istringstream<char, std::char_traits<char>, std::allocator<char> >&)'
CMakeFiles/moje.dir/src/main/cpp/main.cpp.o:(.rodata._ZTV6WriterINSt7__cxx1119basic_istringstreamIcSt11char_traitsIcESaIcEEEE[_ZTV6WriterINSt7__cxx1119basic_istringstreamIcSt11char_traitsIcESaIcEEEE]+0x20): undefined reference to `Writer<std::__cxx11::basic_istringstream<char, std::char_traits<char>, std::allocator<char> > >::write(std::__cxx11::basic_istringstream<char, std::char_traits<char>, std::allocator<char> >&)'

实施如下：

Writer.h

#ifndef WRITER_H
#define WRITER_H

template<typename T>
class Writer {
public:
    virtual ~Writer() {}
    virtual void write(T &in);
};
#endif /* WRITER_H */

Reader.h

#ifndef READER_H
#define READER_H

template<typename T>
class Reader {
public:
    virtual ~Reader() {}
    virtual T read();
};
#endif /* READER_H */

ReadWriter.h

#ifndef READWRITER_H
#define READWRITER_H
#include "Reader.h"
#include "Writer.h"

template<typename R, typename W>
class ReadWriter : public Reader<R>, public Writer<W>{
public:
    virtual ~ReadWriter() {}
};
#endif /* READWRITER_H */

ConfigReadWriter.h

#ifndef CONFIGREADWRITER_H
#define CONFIGREADWRITER_H
#include "header/ReadWriter.h"

class ConfigReadWriter : public ReadWriter<std::ostringstream, std::istringstream> {
public:
    ConfigReadWriter(Config &config) : config_(config) {}
    ~ConfigReadWriter() {}

    std::ostringstream read() override {
        std::ostringstream ss("ConfigReadWriter::read");
        return ss;
    };

    void write(std::istringstream& in) override {
        std::cout << "ConfigReadWriter::write" << std::endl;
    }
private:
    Config& config_;
};
#endif /* CONFIGREADWRITER_H */

Main.cpp：

#include "header/config/Config.h"
#include "header/config/ConfigReadWriter.h"


int main() {
    std::string a = "1";
    Config config(1, a);
    ConfigReadWriter rw(config);
    return 0; 
}

我理解通过保持头部中的实现我不应该发生未定义引用的错误。更正了write方法中的实现以适应接口。还是有编译错误。阅读链接。

答案

请注意，您的实现提供了带有副本的void write(std::istringstream)方法，而未定义的引用用于获取您未在基类void write(std::istringstream &)中实现的virtual void write(T &in);等引用的方法。因此，您应该使用正确的签名更新实现：

virtual void write(T &in) = 0; // no implementation

...

void write(std::istringstream &) override    {
    std::cout << "ConfigReadWriter::write" << std::endl;
}

override说明符确保方法签名与基类中的虚方法签名匹配。