c++ - 混合从 C 和 C++ 编译的目标文件时出现链接器错误

Question

我无法混合使用 C 和 C++ 代码，我使用 gcc 和 g++ 分别编译了 C 和 C++ 代码。 C 代码调用 C++ 函数。我分别编译它们，效果很好。我链接这两个对象以生成一个“.so”文件。当我从 lua 加载这个模块时，模块加载失败说一些 undefined symbol 。我在这里粘贴 C 和 C++ 以及 lua 错误。

File: wrap.c
----------------------------------------------
#include<stdio.h>

//extern "C"{
extern const char* getMobileFromUid(long long );
extern void addToUidHash(long long, char*);
//}
int callcpp (int ac, char **av)
{
    addToUidHash(1, "98866380587");
    fprintf(stderr,"hash:%s",getMobileFromUid(1));
    return 0;
}

File : uid_hash.cc
--------------------------------------------------------
#include <iostream>
#include <string>
#include <map>

typedef std::map<long long, std::string> uidMapType;
uidMapType uidMap;

extern "C"{ 
const char *getMobileFromUid(long long );
void         addToUidHash(long long, char *);
}


//Add the element  to the uid hash 
void 
addToUidHash(long long uid, char *mobile)
{
    uidMap[uid] = mobile;
    return;
}

//print the uid hash 
void 
printUidHash()
{
    uidMapType::const_iterator end = uidMap.end(); 
    for (uidMapType::const_iterator it = uidMap.begin(); it != end; ++it)
    {
        std::cout << "key = " << it->first;
        std::cout << " value = " << it->second << '\n';
    }
    return;
}


//get the mobile number string from the uid of the user 
const char *
getMobileFromUid(long long uid)
{
        uidMapType::iterator iter = uidMap.find(uid);
        if (iter == uidMap.end()) return NULL; 
        return iter->second.c_str();
}


I compile both of them like below 

ravit@ravit-laptop:~$ g++ -c uid_hash.cc -o uid_hash.o 
ravit@ravit-laptop:~$ gcc -c wrap.c -o wrap.o 
ravit@ravit-laptop:~$ ld -shared wrap.o uid_hash.o -o uid_hash.so 


after this i try to load the module from lua and i get an error "undefined" symbol 

ravit@ravit-laptop:~$ lua
Lua 5.1.4  Copyright (C) 1994-2008 Lua.org, PUC-Rio
> require "uid_hash"
error loading module 'uid_hash' from file './uid_hash.so':
    ./uid_hash.so: undefined symbol: _ZNSsaSEPKc
stack traceback:
    [C]: ?
    [C]: in function 'require'
    stdin:1: in main chunk
    [C]: ?
> 

这个 undefined symbol 是什么？

Answer 1

我认为您需要链接到 C++ 库。 c++filt 可以帮助您解码损坏的符号名称:

main% c++filt _ZNSsaSEPKc
std::basic_string<char, std::char_traits<char>, std::allocator<char> >::operator=(char const*)