Question

我正在尝试创建一个嵌入FFMPEG功能的C ++程序。为此，我举了一个FFMPEG示例，并使用g ++对其进行了重新编译（仅在需要时添加extern“ C”）。编译成功，但未定义符号的链接失败。

pipeline = [
    {
        "$match": {   
            "images" : {
                "$ne" : None,
                "$exists": True,
            } 
        }
    },
    {
        "$match": {
            "img_status": {
                "$exists": False,
            }
        }
    },
    {
        "$group":{
            "_id"       : "$vendor_link",
            "images"    : {"$first": "$images"},
            "uuid"      : {"$first": "$uuid"},
            "source"    : {"$first": "$source"}
        }
    },
]
pprint(list(self.collection.aggregate(pipeline)))

检查nm，我发现实际上没有名称修饰，因此外部C似乎运行良好：

const WebSocket = require('ws');
var quote
// BitMEX Connection
'use strict';
const BitMEXClient = require('./index');
const client = new BitMEXClient({testnet: false});
client.on('error', console.error);
client.on('open', () => console.log('Listening for BVOL.'));
client.on('close', () => console.log('Connection closed.'));
client.on('initialize', () => console.log('BitMEX API Connected.'));

client.addStream('XBTUSD', 'trade', function (data, symbol, tableName)
{
  if (!data.length) return;
  var a = data[data.length - 1];
  console.log(a.size,a.timestamp);
});

检查库，对于“缺失”符号之一，我可以看到它已实现

<ion-button color="{{color}}" (click)="action.emit(null)" disabled [attr.disabled]="(condition)?condition:null">                    

 {{title}}</ion-button>

在C语言中编译时，它可以完美运行（当然没有extern C），这让我想知道我还缺少什么？

在下面找到FFMPEG示例代码以供参考（decode_video.cpp）：

cc -I/usr/include/x86_64-linux-gnu -Wall -g -fPIC  -c -o bin/decode_video.o decode_video.cpp

cc -Wl,--export-dynamic,--no-undefined -L /usr/lib/x86_64-linux-gnu/ -shared -lavdevice -lavutil -lavcodec  bin/decode_video.o -o decode_video.so

bin/decode_video.o: In function `decode(AVCodecContext*, AVFrame*, AVPacket*, char const*)':
/home/admin1/ffmpeg_examples/decode_video.cpp:60: undefined reference to `avcodec_send_packet'
/home/admin1/ffmpeg_examples/decode_video.cpp:67: undefined reference to `avcodec_receive_frame'
bin/decode_video.o: In function `main':
/home/admin1/ffmpeg_examples/decode_video.cpp:108: undefined reference to `av_packet_alloc'
/home/admin1/ffmpeg_examples/decode_video.cpp:116: undefined reference to `avcodec_find_decoder'
/home/admin1/ffmpeg_examples/decode_video.cpp:122: undefined reference to `av_parser_init'
/home/admin1/ffmpeg_examples/decode_video.cpp:128: undefined reference to `avcodec_alloc_context3'
/home/admin1/ffmpeg_examples/decode_video.cpp:139: undefined reference to `avcodec_open2'
/home/admin1/ffmpeg_examples/decode_video.cpp:150: undefined reference to `av_frame_alloc'
/home/admin1/ffmpeg_examples/decode_video.cpp:165: undefined reference to `av_parser_parse2'
/home/admin1/ffmpeg_examples/decode_video.cpp:184: undefined reference to `av_parser_close'
/home/admin1/ffmpeg_examples/decode_video.cpp:185: undefined reference to `avcodec_free_context'
/home/admin1/ffmpeg_examples/decode_video.cpp:186: undefined reference to `av_frame_free'
/home/admin1/ffmpeg_examples/decode_video.cpp:187: undefined reference to `av_packet_free'

Answer 1

感谢@WhozCraig帮助我弄清楚了。链接时我以为我保留了完整的库符号时使用了错误的标志，但这是错误的标志。因此，链接器只通过了一次，对象顺序错误（因为我自然认为这没关系）要保留完整的库符号，请将--whole-archive传递给链接器：

-Wl,--whole-archive

无法使用g ++用C ++代码编译C库

1 个答案: