g ++无法找到标题，但我确实包含了它们

I am starting on c++ and already going wrong ...

我开始使用c ++并且已经出错...

I am trying to compile a small test of levelDB :

我正在尝试编译levelDB的一个小测试:

#include <assert.h>
#include "leveldb/db.h"

using namespace std;

int main() {
  leveldb::DB* db;
  leveldb::Options options;
  options.create_if_missing = true;
  leveldb::Status status = leveldb::DB::Open(options, "/tmp/testdb", &db);
  assert(status.ok());

  return 1;
}

Here is the g++ command :

这是g ++命令:

g++ -I include/ testLevelDB.cpp

Output:

/tmp/ccuBnfE7.o: In function `main':
testLevelDB.cpp:(.text+0x14): undefined reference to `leveldb::Options::Options()'
testLevelDB.cpp:(.text+0x57): undefined reference to `leveldb::DB::Open(leveldb::Options const&, std::string const&, leveldb::DB**)'

The include folder is the one with the levelDB headers.

include文件夹是具有levelDB标头的文件夹。

2 个解决方案

#1

You need to tell the linker to link to the leveldb library such as

您需要告诉链接器链接到leveldb库,例如

g++ -I include/ testLevelDB.cpp -lleveldb

But this won't work if the library is not in /usr/lib or /usr/local/lib for that case assuming the libleveldb.so exists in some path called $LEVELDB_PATH you need to do

但是,如果库不在/ usr / lib或/ usr / local / lib中,假设libleveldb.so存在于某个名为$ LEVELDB_PATH的路径中,则需要执行此操作

g++ -I include -L $LEVELDB_PATH testLevelDB.cpp -lleveldb

-L is much like -I but it tells the linker where to looks for libraries.

-L非常像-I但它告诉链接器在哪里查找库。

Also since you seem to be new to gcc world, please have a look at this gcc intro document.

此外,因为你似乎是gcc世界的新手,请看一下这个gcc介绍文档。

#2

It is a linkage error. Not related to the headers. Did you link with this lib (-l..) ?

这是一个连锁错误。与标题无关。你有没有链接这个lib(-l ..)?

#1