下午在用 gcc/g++ 编译 c/c++ 代码时遇到了报错：
paxos-kv/DBImpl.o: In function `KeyHitEntityID(unsigned long, rocksdb::Slice const&)':
/home/zhang/paxosstore/./paxos-kv/Coding.h:277: multiple definition of `KeyHitEntityID(unsigned long, rocksdb::Slice const&)'
paxos-kv/PLogImpl.o:/home/zhang/paxosstore/./paxos-kv/Coding.h:277: first defined here
paxos-kv/ServiceImpl.o: In function `__gnu_cxx::new_allocator<std::_Rb_tree_node<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, std::pair<KVStatus, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > > >::~new_allocator()':
/home/zhang/paxosstore/./paxos-kv/Coding.h:277: multiple definition of `KeyHitEntityID(unsigned long, rocksdb::Slice const&)'
paxos-kv/PLogImpl.o:/home/zhang/paxosstore/./paxos-kv/Coding.h:277: first defined here
paxos-kv/Server.o: In function `KeyHitEntityID(unsigned long, rocksdb::Slice const&)':
/home/zhang/paxosstore/./paxos-kv/Coding.h:277: multiple definition of `KeyHitEntityID(unsigned long, rocksdb::Slice const&)'
paxos-kv/PLogImpl.o:/home/zhang/paxosstore/./paxos-kv/Coding.h:277: first defined here
paxos-kv/DBImpl.o: In function `clsDBImpl::GetEntityMeta(unsigned long, unsigned long&, unsigned int&)':
/home/zhang/paxosstore/paxos-kv/DBImpl.cpp:92: undefined reference to `clsDBImpl::GetEntityMeta(unsigned long, unsigned long&, unsigned int&, rocksdb::Snapshot const*)'
paxos-kv/ServiceImpl.o: In function `clsServiceImpl::GetDBEntityMeta(grpc::ServerContext&, kv_rpc::GetDBRequest const&, kv_rpc::GetDBResponse&)':
/home/zhang/paxosstore/paxos-kv/ServiceImpl.cpp:97: undefined reference to `clsDBImpl::GetEntityMeta(unsigned long, unsigned long&, unsigned int&, rocksdb::Snapshot const*)'
collect2: error: ld returned 1 exit status
Makefile:154: recipe for target 'db_server' failed
make: *** [db_server] Error 1
rm certain/src/Certain.pb.cc
报错的重点是first defined here In function 和multiple definition of
测试示例代码如下：
util.h
#pragma once
#include <stdio.h>
void print(){
printf("test");
}
a.c
#include "util.h"
void a(){
print();
}
main.c
#include "util.h"
#include "a.c"
int main(void){
a();
}
编译：
gcc -c a.c -o a.out
gcc -c main.c -o main.out
gcc main.out a.out -o main
报错如下：
-> % gcc main.out a.out -o main
a.out: In function `print':
a.c:(.text+0x0): multiple definition of `print'
main.out:main.c:(.text+0x0): first defined here
a.out: In function `a':
a.c:(.text+0x18): multiple definition of `a'
main.out:main.c:(.text+0x18): first defined here
collect2: error: ld returned 1 exit status
报错的原因是虽然头文件指定只编译一次，但每次编译时，都编译了一次，最后链接的时候自然就报错了。
解决方法一：头文件只声明，函数主体内容放到.c/.cpp中
解决方法二：头文件的函数加上关键字inline，直接把函数编译进去，自然不会冲突。
文档信息
- 本文作者：last2win
- 本文链接：https://last2win.com/2020/03/04/gcc-error/
- 版权声明：自由转载-非商用-非衍生-保持署名（创意共享3.0许可证）