問(wèn)題描述

我有三個(gè)文件.main.cpp 的內(nèi)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(dāng)我嘗試使用以下命令編譯這些文件時(shí)，出現(xiàn)未定義的引用錯(cuò)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?qū)崿F(xiàn)有問(wèn)題嗎?為什么我會(huì)收到這些鏈接錯(cuò)誤:?

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

推薦答案

非專(zhuān)用模板的實(shí)現(xiàn)必須對(duì)使用它的翻譯單元可見(jiàn).

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(shí)現(xiàn)，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(guò)兩種方式實(shí)現(xiàn):

This can be achieved in two ways:

1) 將實(shí)現(xiàn)移到標(biāo)題內(nèi).

1) Move the implementation inside the header.

2) 如果您想將其分開(kāi)，請(qǐng)將其移動(dòng)到包含在原始標(biāo)題中的不同標(biāo)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(guān)于對(duì)模板函數(shù)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(duì)大家有所幫助，也希望大家多多支持html5模板網(wǎng)！