模板接口的使用引起“未定义的引用”

Usage of templated interfaces cause “Undefined reference to”

本文关键字：未定义 引用 接口      更新时间：2023-10-16

，所以我会收到以下编译错误：

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> >&)'

实现如下：

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 */

piffimreadWriter.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，通过将实现保持在标题中，我不应出现未定义的参考。更正了写入方法中的实现以适合接口。仍然有编译错误。读取链接。

请注意，您的实现提供了 void write(std::istringstream)方法，而未定义的参考是用于使用诸如void write(std::istringstream &)之类的参考，而您未在基类virtual void write(T &in);上实现的参考。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指定符确保方法签名匹配基类中的虚拟方法签名。

相关文章：