在模板功能上的模板专业化声明

Question

我会得到对模板专业化的长长的frombigendin＆lt long＆gt;（unsigned char*）的不确定的引用。

请参阅此处： https://onlinegdb.com/aagktqj2b

我有这个结构

：

template <class T>
T fromBigEndin(uint8_t *buf);

template <>
int64_t fromBigEndin<int64_t>(uint8_t *buf);
template <>
long long fromBigEndin<long long>(unsigned char *buf);

util.cpp

template<class T>
T fromBigEndin(uint8_t *buf) {
    T number = 0;
    uint8_t nBytes = sizeof(T);
    uint8_t i;

    for (i = 0; i < nBytes; i += 1) {
        number += buf[i] << (16 * (nBytes - i - 1));
    }

    return number;
}

headerimpl.h

#include "util.h"

void handleOpenSession(uint8_t *data) {
    uint8_t *uid = (uint8_t *)malloc(8);
    memcpy(uid, data + 1, 8);
    int64_t uidNbr = fromBigEndin<int64_t>(uid);
}

来自@Anooprana响应，将实现放在标题文件中，我想知道是否可以将实现进行实现在单独的文件中。

关于我如何强制对frombigendin＆lt; int64_t＆gt;（）的汇编的想法？

我还试图将专业人士移至util.cpp，但也不起作用。

该代码本身在单个文件中和不同声明中起作用：

• https:/ https://www.mycompiler.io/ view/9 yri89bnza0
• https：/

Answer 1

方法1

您需要将功能模板的实现放入标题文件本身中。因此，它看起来像：

util.h

#pragma once  //include guard added
template <class T>
T fromBigEndin(uint8_t *buf);

//definition
template <> int64_t fromBigEndin<int64_t>(uint8_t *buf)
{
    return 53;
}
//definition 
template <> long long fromBigEndin<long long>(unsigned char *buf)
{ 
    return 54;
}


//implementation in header file itself
template<class T>
T fromBigEndin(uint8_t *buf) {
    T number = 0;
    uint8_t nBytes = sizeof(T);
    uint8_t i;

    for (i = 0; i < nBytes; i += 1) {
        number += buf[i] << (16 * (nBytes - i - 1));
    }

    return number;
}

headerimpl.h

#pragma once
#include "util.h"

void handleOpenSession(uint8_t *data) {
    //add code here 
}

main.cpp

#include <iostream>
#include "util.h"
int main()
{
    
    return 0;
}

工作演示

方法2

这里我们使用显式模板实例。

util.h

#pragma once
#include <cstdint>
template <class T>
T fromBigEndin(uint8_t *buf);

headerimpl.h

#pragma once
#include "util.h"


void handleOpenSession(uint8_t *data) {
    uint8_t *uid = (uint8_t *)malloc(8);
    memcpy(uid, data + 1, 8);
    int64_t uidNbr = fromBigEndin<int64_t>(uid);
}

util.cpp

#include "util.h"

template<class T>
T fromBigEndin(uint8_t *buf) {
    T number = 0;
    uint8_t nBytes = sizeof(T);
    uint8_t i;

    for (i = 0; i < nBytes; i += 1) {
        number += buf[i] << (16 * (nBytes - i - 1));
    }

    return number;
}

//no angle brackets used here
template int64_t fromBigEndin<int64_t>(uint8_t *buf);
template long long fromBigEndin<long long>(unsigned char *buf);

main.cpp

#include <iostream>

#include "util.h"
int main()
{
    
    return 0;
}