問題描述

我有三個文件.main.cpp 的內容是

I have three files . The contents of main.cpp are

#include<iostream>
#include<QString>

#include "util.h"

int main()
{
    using Util::convert2QString;

    using namespace std;
    int n =22;
    QString tmp = convert2QString<int>(n);

    return 0;
}

util.h

namespace Util
{
    template<class T>
    QString convert2QString(T type , int digits=0);
}

util.cpp

namespace Util
{
    template<class T>
        QString convert2QString(T type, int digits=0)
        {
            using std::string;

            string temp = (boost::format("%1%") % type).str();

            return QString::fromStdString(temp);
        }
}

當我嘗試使用以下命令編譯這些文件時，出現未定義的引用錯誤

When I try to compile these files with following command I get undefined reference error

vickey@tb:~/work/trash/template$ g++ main.cpp  util.cpp -lQtGui -lQtCore  -I. -I/usr/local/Trolltech/Qt-4.8.0/include/QtCore -I/usr/local/Trolltech/Qt-4.8.0/include/QtGui -I/usr/local/Trolltech/Qt-4.8.0/include
/tmp/cca9oU6Q.o: In function `main':
main.cpp:(.text+0x22): undefined reference to `QString Util::convert2QString<int>(int, int)'
collect2: ld returned 1 exit status

模板聲明或實現有問題嗎?為什么我會收到這些鏈接錯誤:?

Is there something wrong with the template declaration or implementation ? why M I getting these linking errors :?

推薦答案

非專用模板的實現必須對使用它的翻譯單元可見.

The implementation of a non-specialized template must be visible to a translation unit that uses it.

編譯器必須能夠看到實現，才能為代碼中的所有特化生成代碼.

The compiler must be able to see the implementation in order to generate code for all specializations in your code.

這可以通過兩種方式實現:

This can be achieved in two ways:

1) 將實現移到標題內.

1) Move the implementation inside the header.

2) 如果您想將其分開，請將其移動到包含在原始標題中的不同標題中:

2) If you want to keep it separate, move it into a different header which you include in your original header:

util.h

namespace Util
{
    template<class T>
    QString convert2QString(T type , int digits=0);
}
#include "util_impl.h"

util_impl.h

namespace Util
{
    template<class T>
        QString convert2QString(T type, int digits=0)
        {
            using std::string;

            string temp = (boost::format("%1") % type).str();

            return QString::fromStdString(temp);
        }
}

這篇關于對模板函數的未定義引用的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！