我在C项目中使用来自ffmpeg的libavcodec和libavformat库.链接-lavcodec -lavformat与g编译器工作正常,但我不确定当我尝试使用在automake项目中编译的相同代码时出了什么问题.

工作正常：

g++ -o test -D__STDC_CONSTANT_MACROS -lavcodec -lavformat test.cpp

不工作Makefile.am：

binaryname_LDFLAGS= -lavcodec -lavformat

错误：

....
/usr/lib/gcc/i686-linux-gnu/4.6/../../../i386-linux-gnu/libavformat.a(nut.o):function 
ff_nut_add_sp: error: undefined reference to 'av_tree_node_size'
/usr/lib/gcc/i686-linux-gnu/4.6/../../../i386-linux-gnu/libavformat.a(nut.o):function 
ff_nut_add_sp: error: undefined reference to 'av_tree_insert'
/usr/lib/gcc/i686-linux-gnu/4.6/../../../i386-linux-gnu/libavformat.a(nut.o):function 
ff_nut_free_sp: error: undefined reference to 'av_tree_enumerate'
/usr/lib/gcc/i686-linux-gnu/4.6/../../../i386-linux-gnu/libavformat.a(nut.o):function 
ff_nut_free_sp: error: undefined reference to 'av_tree_destroy'
/usr/lib/gcc/i686-linux-gnu/4.6/../../../i386-linux-gnu/libavformat.a(rtp.o):function 
ff_rtp_get_payload_type: error: undefined reference to 'av_opt_get_int'
...

也没工作：

LDFLAGS=...-lavcodec -lavformat

错误：

src/dsp/audioDecoder.cpp:99: error: undefined reference to 'av_register_all'
src/dsp/audioDecoder.cpp:101: error: undefined reference to 'avcodec_find_decoder'
src/dsp/audioDecoder.cpp:109: error: undefined reference to 'avcodec_alloc_context'
src/dsp/audioDecoder.cpp:120: error: undefined reference to 'avcodec_open2'
src/dsp/audioDecoder.cpp:125: error: undefined reference to 'av_init_packet'
src/dsp/audioDecoder.cpp:188: error: undefined reference to 'avcodec_decode_audio3'

在第二种情况下,如果我没有设置任何链接器,则无法找到包含头,因此链接器似乎以某种方式被识别.

使V = 1返回：

make  all-am
make[1]: Go to '/path/to/trunk'
/bin/bash ./libtool --tag=CXX   --mode=link g++  -O2 -lrt -D__STDC_CONSTANT_MACROS   -o binaryname progsrc/binaryname/binaryname-binaryname.o    -lm  -lpthread -ldl -lmygeneratedlibrary
libtool: link: g++ -O2 -D__STDC_CONSTANT_MACROS -o binaryname progsrc/binaryname/binaryname-binaryname.o  -lm /path/to//trunk/.libs/lmygeneratedlibrary.a -lrt -lavutil -lavcodec -lavformat -lpthread -ldl
make[1]: Leave '/path/to/trunk'

我在这做错了什么？

解决方法:

CPPFLAGS用于C预处理器.不是C标志.这是CXXFLAGS.对于链接器的东西,你想要LDFLAGS.

您的Makefile.am似乎不遵循规范的Makefile.am格式.你可能想要它更像(taken from here)：

# what flags you want to pass to the C compiler & linker
CFLAGS = # C compiler flags
LDFLAGS = # Linker flags

# this lists the binaries to produce, the (non-PHONY, binary) targets in
# the previous manual Makefile
bin_PROGRAMS = targetbinary1 targetbinary2 [...] targetbinaryN
targetbinary1_SOURCES = targetbinary1.c myheader.h [...]
targetbinary2_SOURCES = targetbinary2.c
.
.
targetbinaryN_SOURCES = targetbinaryN.c

此外,请确保在包含FFmpeg的标题时,用extern“C”包围它们.例如：

extern "C" {
#include <libavformat/avformat.h>
}