我正在尝试使用GStreamer C库中的某些函数来编译C ++程序。在MacOS Catelina上使用g ++(安装了Homebrew的9.2版本)时,程序可以正常编译和链接,但是在Ubuntu 18.04上使用g ++时,由于未定义的引用,它在链接阶段失败。我没有在两个平台之间的代码方面进行任何更改,代码非常简单,唯一使用的外部库是GStreamer。
错误:
g++ `pkg-config --cflags --libs gstreamer-1.0` -std=gnu++11 -Wall -Wextra -c -o img_sys.o img_sys.cpp
g++ -std=gnu++11 -Wall -Wextra -c -o img_cameras.o img_cameras.cpp
g++ `pkg-config --cflags --libs gstreamer-1.0` -std=gnu++11 -Wall -Wextra -c -o img_cameras_gstreamer.o img_cameras_gstreamer.cpp
g++ `pkg-config --cflags --libs gstreamer-1.0` -std=gnu++11 -Wall -Wextra -o img_sys img_sys.o img_cameras.o img_cameras_gstreamer.o
img_cameras_gstreamer.o: In function `gst_caps_unref':
img_cameras_gstreamer.cpp:(.text+0x14): undefined reference to `gst_mini_object_unref'
img_cameras_gstreamer.o: In function `ImgSys::GStreamerCameras::msgReceivedCallback(_GstBus*, _GstMessage*, void*)':
img_cameras_gstreamer.cpp:(.text+0x75): undefined reference to `gst_message_get_structure'
img_cameras_gstreamer.cpp:(.text+0xa3): undefined reference to `gst_structure_get'
img_cameras_gstreamer.cpp:(.text+0x109): undefined reference to `gst_message_parse_error'
img_cameras_gstreamer.cpp:(.text+0x125): undefined reference to `g_print'
...
collect2: error: ld returned 1 exit status
makefile:10: recipe for target 'img_sys' failed
make: *** [img_sys] Error 1
Makefile:
CXX = g++
CXXFLAGS = -std=gnu++11 -Wall -Wextra
GSTREAMER = `pkg-config --cflags --libs gstreamer-1.0`
img_sys: img_sys.o img_cameras.o img_cameras_gstreamer.o
$(CXX) $(GSTREAMER) $(CXXFLAGS) -o $@ $^
img_sys.o: img_sys.cpp
$(CXX) $(GSTREAMER) $(CXXFLAGS) -c -o $@ $^
img_cameras.o: img_sys.hpp
img_cameras_gstreamer.o: img_cameras_gstreamer.cpp
$(CXX) $(GSTREAMER) $(CXXFLAGS) -c -o $@ $^
img_cameras_gstreamer.cpp包括:
#include <iostream>
#include <string>
#include <vector>
#include <gst/gst.h>
#include "img_sys.hpp"
#include "img_cameras_gstreamer.hpp"
img_cameras_gstreamer.hpp:
#ifndef IMG_CAMERAS_GSTREAMER_GUARD_H
#define IMG_CAMERAS_GSTREAMER_GUARD_H
#include <gst/gst.h>
#include "img_sys.hpp"
namespace ImgSys {
class GStreamerCameras: public ImgSys::Cameras {
private:
GstElement *pipeline;
GMainLoop *loop;
guint bus_watch_id;
static gboolean msgReceivedCallback(__attribute__((unused)) GstBus*, GstMessage*, gpointer);
static gboolean pipelineTimeOut(__attribute__((unused)) gpointer);
public:
void build();
void beginCapture();
};
}
#endif
对不起所有代码,希望尽可能地解释清楚。
我在这里找到问题的答案:https://stackoverflow.com/a/8359200/4638141
结果是,较新版本的Ubuntu gcc需要以不同的顺序使用其pkg-config选项(摘自链接文章:]
gcc `pkg-config gstreamer-0.10 --cflags` main.c -o player.out `pkg-config gstreamer-0.10 --libs`