c++ - 重载时出现 undefined reference 错误

Question

所以我四处寻找这个问题的答案，但没有一个解决方案适合我。我在一个单独的类“Operators.cpp”中重载了运算符<<，具体代码如下:

#include "Rolo.h"
#include "RoloHeader.h"
#include "RoloParsedRecord.h"
#include "RoloRawRecord.h"


std::ostream& operator <<(std::ostream& outstream, const Rolo& rolo){
    string roloData = rolo.toString();
    outstream << roloData;
    return outstream;
}

std::ostream& operator <<(std::ostream& outstream, const RoloHeader& roloHeader){
    string roloHeaderData = roloHeader.toString();
    outstream << roloHeaderData;
    return outstream;
}

std::ostream& operator <<(std::ostream& outstream, const RoloParsedRecord& rpRecord){
    string rpRecordData = rpRecord.toString();
    outstream << rpRecordData;
    return outstream;
}

std::ostream& operator <<(std::ostream& outstream, const RoloRawRecord& rrRecord){
    string rrRecordData = rrRecord.toString();
    outstream << rrRecordData;
    return outstream;
}

在 Rolo.h 中:

friend ostream& operator <<(ostream& outputStream, const Rolo& rolo);
friend ostream& operator <<(ostream& outputStream, const RoloHeader& roloHeader);
friend ostream& operator <<(ostream& outputStream, const RoloParsedRecord& rpRecord);

它在 Main.cpp 中被称为:

Rolo theRolo;
theRolo.readRolo(inStream); //no issues here
theRolo.sortRolo(sortTag); //no issues here either
outStream << theRolo.toStringFormatted(); //prints out exactly as wanted, no issues
outStream << theRolo; //this is where it chokes

当我编译它时，我得到:

Main.o: In function `main':
Main.cpp:(.text.startup+0x3f9): undefined reference to `operator<<(std::ostream&, Rolo&)'
collect2: error: ld returned 1 exit status
make: *** [Aprog] Error 1

还有其他类，运行完美。仅当我尝试使用重载的 << 而不是 toStringFormatted() 函数时才会出现此问题。

所以我的问题是:这里出了什么问题？为什么它是未定义的？而且，最重要的是，我能做些什么来修复它？

Answer 1

你如何编译这个？你编译和链接分开吗？您可能会做什么:您通过包含 Rolo.h 对 Main.cpp 说存在重载运算符。它编译。但是链接器找不到它的实现。