c++ - 链接器找不到命名空间的函数

Question

请参阅下面的代码。它有问题，因为链接器提示它找不到 Memory 的函数，但我不明白为什么。

内存.h

#pragma once
#include "includes.h" //it just includes other strandard headers.

class MemoryUnit
{
public:
    MemoryUnit() {}
    virtual int getValue() = 0;
    virtual int getSize() = 0;
    virtual void setValue(int) = 0;
    virtual ~MemoryUnit() {};
};
class Byte : public MemoryUnit
{
    int value;
public:
    static int size;
    Byte(int byte) :value(byte) {};
    int getSize() { return size; }
    int getValue() { return value; };
    void setValue(int byte) { value = byte; }
    ~Byte() {};
};
namespace Memory
{
    extern int size;
    extern MemoryUnit** map;
    void checkAddress(int address);
    int read(int adress);
    MemoryUnit* getOperation(int address);
    void write(int adress, MemoryUnit* data);
    void writeByte(int adress, int data);
}

内存.cpp

#include "includes.h"
#include "memory.h"
#include "simulator.h" // it contains only externed constants.

namespace Memory
{
    int size = 0;
    MemoryUnit** map = NULL;
    inline MemoryUnit* getOperation(int address)
    {
        return map[address];
    }
    inline void checkAddress(int address)
    {
        if (address < 0 || address >= MAX_MEMORY_SIZE)
            throw std::out_of_range("Invalid memory address.");
    }
    inline int read(int address)
    {
        checkAddress(address);
        return map[address]->getValue();
    }
    inline void write(int address, MemoryUnit* data)
    {
        checkAddress(address);
        delete map[address];
        map[address] = data;
    }
    inline void writeByte(int address, int data)
    {
        checkAddress(address);
        map[address]->setValue(data);
    }
}

类/命名空间 memory.h 声明的所有地方都包含 memory.h。下面的代码有什么问题吗？

编辑: 我正在使用 Visual Studio 2015。 我在构建项目时遇到的错误:

LNK1120 5 unresolved externals  simulator.exe
LNK2019 unresolved external symbol "void __cdecl Memory::writeByte(int,int)" referenced in function "void __cdecl ALU::setFlags(int)" alu.obj
LNK2001 unresolved external symbol "void __cdecl Memory::writeByte(int,int)" cu.obj
LNK2019 unresolved external symbol "class MemoryUnit * __cdecl Memory::getOperation(int)" referenced in function "void __cdecl CU::run(void)" cu.obj
LNK2001 unresolved external symbol "void __cdecl Memory::writeByte(int,int)" helpers.obj
LNK2019 unresolved external symbol "void __cdecl Memory::write(int,class MemoryUnit *)" referenced in function "void __cdecl readProgramCommands(void)" helpers.obj
LNK2001 unresolved external symbol "public: virtual int __thiscall MemoryPointer::getValue(void)" helpers.obj
LNK2001 unresolved external symbol "public: virtual int __thiscall IndirectMemoryPointer::getAddress(void)" helpers.obj
LNK2001 unresolved external symbol "void __cdecl Memory::writeByte(int,int)" main.obj

alu.h 和 alu.cpp 第一个错误:

//alu.h
#pragma once
#include "includes.h"
#include "operation.h"
namespace ALU
{
    int operation(Operation* op);
    void setFlags(int result);
}
//alu.cpp
#include "includes.h"
#include "simulator.h"
#include "alu.h"
#include "memory.h"
#include "operation.h"
namespace ALU
{
    int operation(Operation* operation)
    {
        // ...
        setFlags(result);
        return result;
    }
    inline void setFlags(int result)
    {
        Memory::writeByte(FLAG_Z, result == 0);
        // ...
    }
}

Answer 1

您需要将内联函数定义放在您的头文件中(它们都必须出现在使用它们的每个翻译单元中)，您可以将声明和定义分开，但两者都必须在头文件中。此外，它们必须声明为内联。

N4140 dcl.fct.spec 7.1.2.4

An inline function shall be defined in every translation unit in which it is odr-used and shall have exactly the same definition in every case (3.2). [ Note: A call to the inline function may be encountered before its definition appears in the translation unit. —end note ] If the definition of a function appears in a translation unit before its first declaration as inline, the program is ill-formed.