链接与libavcodec，仍然看到未定义的引用

我想编译一个libavcodec的例子。我收到以下错误：链接与libavcodec，仍然看到未定义的引用

[email protected]:~/p/avtest$ g++ main.cpp -o main -lavcodec 
main.cpp: In function ‘void audio_decode_example(const char*, const char*)’: 
main.cpp:57:15: warning: ‘int avcodec_decode_audio4(AVCodecContext*, AVFrame*, int*, const AVPacket*)’ is deprecated [-Wdeprecated-declarations] 
     len = avcodec_decode_audio4(c, decoded_frame, &got_frame, &avpkt); 
       ^~~~~~~~~~~~~~~~~~~~~ 
In file included from main.cpp:1:0: 
/usr/include/x86_64-linux-gnu/libavcodec/avcodec.h:4773:5: note: declared here 
int avcodec_decode_audio4(AVCodecContext *avctx, AVFrame *frame, 
    ^~~~~~~~~~~~~~~~~~~~~ 
main.cpp:57:73: warning: ‘int avcodec_decode_audio4(AVCodecContext*, AVFrame*, int*, const AVPacket*)’ is deprecated [-Wdeprecated-declarations] 
     len = avcodec_decode_audio4(c, decoded_frame, &got_frame, &avpkt); 
                     ^
In file included from main.cpp:1:0: 
/usr/include/x86_64-linux-gnu/libavcodec/avcodec.h:4773:5: note: declared here 
int avcodec_decode_audio4(AVCodecContext *avctx, AVFrame *frame, 
    ^~~~~~~~~~~~~~~~~~~~~ 
/tmp/ccbXVtbs.o: In function `audio_decode_example(char const*, char const*)': 
main.cpp:(.text+0x37): undefined reference to `av_init_packet(AVPacket*)' 
main.cpp:(.text+0x63): undefined reference to `avcodec_find_decoder(AVCodecID)' 
main.cpp:(.text+0xa4): undefined reference to `avcodec_alloc_context3(AVCodec const*)' 
main.cpp:(.text+0xf1): undefined reference to `avcodec_open2(AVCodecContext*, AVCodec const*, AVDictionary**)' 
main.cpp:(.text+0x19c): undefined reference to `av_free(void*)' 
main.cpp:(.text+0x203): undefined reference to `av_frame_alloc()' 
main.cpp:(.text+0x266): undefined reference to `avcodec_decode_audio4(AVCodecContext*, AVFrame*, int*, AVPacket const*)' 
main.cpp:(.text+0x2b8): undefined reference to `av_get_bytes_per_sample(AVSampleFormat)' 
main.cpp:(.text+0x460): undefined reference to `avcodec_close(AVCodecContext*)' 
main.cpp:(.text+0x46c): undefined reference to `av_free(void*)' 
main.cpp:(.text+0x47b): undefined reference to `av_frame_free(AVFrame**)' 
collect2: error: ld returned 1 exit status

正如你可以看到我与libavcodec链接，但仍然得到未定义的引用。还有什么我必须链接以获得这些符号定义？

来源

2017-07-18 jcarpenter2

可能重复[什么是未定义的引用/未解析的外部符号错误，以及如何解决它？]（https://stackoverflow.com/questions/12573816/what-is-an-undefined-reference-unresolved-外部符号错误和如何-DO-修复） – patatahooligan

我问IRC，答案是extern "C"。在源文件中

extern "C" { 
    #include <libavcodec/avcodec.h> 
}

，现在没有错误编译：我改变了这个：

#include <libavcodec/avcodec.h>

了这一点。

来源

2017-07-18 21:28:07 jcarpenter2

链接与libavcodec，仍然看到未定义的引用

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