未找到avcodec符号

Question

我正在尝试在FFMPEG库中构建示例代码，我在项目中添加了libavcode.h和libavcode.a，并将头搜索usr/local/include和库搜索设置为usr/local/lib

当我编译这个例子时，我得到了这个错误... (所有这些错误都与avcodec库有关)

{

Undefined symbols:
 "avcodec_find_encoder(CodecID)", referenced from:
  video_encode_example(char const*, CodecID)in main.o
  "avcodec_open2(AVCodecContext*, AVCodec*, AVDictionary**)", referenced from:
  video_encode_example(char const*, CodecID)in main.o
  video_decode_example(char const*, char const*)in main.o
  "av_init_packet(AVPacket*)", referenced from:
  video_decode_example(char const*, char const*)in main.o
  "av_free(void*)", referenced from:
  video_encode_example(char const*, CodecID)in main.o
  video_encode_example(char const*, CodecID)in main.o
  video_encode_example(char const*, CodecID)in main.o
  video_decode_example(char const*, char const*)in main.o
  video_decode_example(char const*, char const*)in main.o
  "avcodec_alloc_context3(AVCodec*)", referenced from:
  video_encode_example(char const*, CodecID)in main.o
  video_decode_example(char const*, char const*)in main.o
  "av_opt_set(void*, char const*, char const*, int)", referenced from:
  video_encode_example(char const*, CodecID)in main.o
  "av_image_alloc(unsigned char**, int*, int, int, PixelFormat, int)", referenced from:
  video_encode_example(char const*, CodecID)in main.o
  "avcodec_encode_video(AVCodecContext*, unsigned char*, int, AVFrame const*)", referenced from:
  video_encode_example(char const*, CodecID)in main.o
  video_encode_example(char const*, CodecID)in main.o
  "avcodec_register_all()", referenced from:
  _main in main.o
  "avcodec_find_decoder(CodecID)", referenced from:
  video_decode_example(char const*, char const*)in main.o
  "avcodec_decode_video2(AVCodecContext*, AVFrame*, int*, AVPacket const*)", referenced from:
  video_decode_example(char const*, char const*)in main.o
  video_decode_example(char const*, char const*)in main.o
  "avcodec_close(AVCodecContext*)", referenced from:
  video_encode_example(char const*, CodecID)in main.o
  video_decode_example(char const*, char const*)in main.o
  "avcodec_alloc_frame()", referenced from:
  video_encode_example(char const*, CodecID)in main.o
  video_decode_example(char const*, char const*)in main.o
 ld: symbol(s) not found
 collect2: ld returned 1 exit status

}你知道我为什么会有这个问题吗？

谢谢

Answer 1

解决方案是将此代码添加到标题中，因为我猜FFMPEG是用C编写的

extern "C"
{
#ifndef __STDC_CONSTANT_MACROS
#define __STDC_CONSTANT_MACROS
#endif
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include "avassert.h"
#include "avutil.h"
#include "intreadwrite.h"
#include "mem.h"
 }