extern "C" { #include <libavcodec/avcodec.h> }添加在哪里

您可以将 `extern "C"` 块添加到 `camera_driver.cpp` 文件的开头，如下所示：

#include "camera_driver.h"

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

// Rest of the code in camera_driver.cpp

请确保将这段代码添加到 `#include "camera_driver.h"` 的下方。这样可以确保在包含其他头文件之前，正确声明了 FFmpeg 库的 C 函数。

如果您还有其他问题，请随时提问。

相关问题

windows ffmpeg extern "C" #include

<unistd.h> is a header file that is typically used in Unix-based operating systems, such as Linux or macOS. It provides access to various system calls and constants, including the close() function for closing file descriptors.

In Windows, the equivalent functionality is provided by the Windows API. To include the necessary headers for using Windows API functions, you would typically include <windows.h> instead of <unistd.h>. However, please note that the "extern "C"" syntax is not used when including header files in C or C++ code. It is used in function declarations to indicate that the function should use C linkage, which affects how the function name is mangled by the compiler.

If you are working with FFmpeg on Windows, you would typically include the necessary FFmpeg headers, such as <libavformat/avformat.h> or <libavcodec/avcodec.h>, depending on your specific needs. These headers provide the necessary declarations and definitions for working with FFmpeg's functionality.

/root/catkin_uc/src/usb_cam/src/camera_driver.cpp: In destructor ‘virtual usb_cam::AbstractV4LUSBCam::~AbstractV4LUSBCam()’: /root/catkin_uc/src/usb_cam/src/camera_driver.cpp:239:5: error: ‘av_packet_free’ was not declared in this scope av_packet_free(&avpkt); ^~~~~~~~~~~~~~ /root/catkin_uc/src/usb_cam/src/camera_driver.cpp:239:5: note: suggested alternative: ‘av_packet_ref’ av_packet_free(&avpkt); ^~~~~~~~~~~~~~ av_packet_ref /root/catkin_uc/src/usb_cam/src/camera_driver.cpp: In static member function ‘static bool usb_cam::AbstractV4LUSBCam::init_decoder()’: /root/catkin_uc/src/usb_cam/src/camera_driver.cpp:379:13: error: ‘av_packet_alloc’ was not declared in this scope avpkt = av_packet_alloc(); ^~~~~~~~~~~~~~~ /root/catkin_uc/src/usb_cam/src/camera_driver.cpp:379:13: note: suggested alternative: ‘av_image_alloc’ avpkt = av_packet_alloc(); ^~~~~~~~~~~~~~~ av_image_alloc /root/catkin_uc/src/usb_cam/src/camera_driver.cpp: In static member function ‘static bool usb_cam::AbstractV4LUSBCam::decode_ffmpeg(const void*, int, usb_cam::camera_image_t*)’: /root/catkin_uc/src/usb_cam/src/camera_driver.cpp:779:8: error: ‘avcodec_send_packet’ was not declared in this scope if(avcodec_send_packet(avcodec_context, avpkt) < 0) ^~~~~~~~~~~~~~~~~~~ /root/catkin_uc/src/usb_cam/src/camera_driver.cpp:779:8: note: suggested alternative: ‘av_append_packet’ if(avcodec_send_packet(avcodec_context, avpkt) < 0) ^~~~~~~~~~~~~~~~~~~ av_append_packet /root/catkin_uc/src/usb_cam/src/camera_driver.cpp:792:9: error: ‘avcodec_receive_frame’ was not declared in this scope if (avcodec_receive_frame(avcodec_context, avframe_camera) < 0) ^~~~~~~~~~~~~~~~~~~~~ /root/catkin_uc/src/usb_cam/src/camera_driver.cpp:792:9: note: suggested alternative: ‘avcodec_free_frame’ if (avcodec_receive_frame(avcodec_context, avframe_camera) < 0) ^~~~~~~~~~~~~~~~~~~~~ avcodec_free_frame usb_cam/CMakeFiles/v4l_driver.dir/build.make:110: recipe for target 'usb_cam/CMakeFiles/v4l_driver.dir/src/camera_driver.cpp.o' failed make[2]: *** [usb_cam/CMakeFiles/v4l_driver.dir/src/camera_driver.cpp.o] Error 1 CMakeFiles/Makefile2:656: recipe for target 'usb_cam/CMakeFiles/v4l_driver.dir/all' failed make[1]: *** [usb_cam/CMakeFiles/v4l_driver.dir/all] Error 2 Makefile:140: recipe for target 'all' failed make: *** [all] Error 2 Invoking "make -j4 -l4" failed

根据错误信息，看起来在您的代码中缺少对FFmpeg相关函数的声明。建议您在使用这些函数之前添加FFmpeg头文件的包含语句。

请将以下行添加到 `camera_driver.cpp` 文件的开头，即在任何其他 `#include` 语句之前：

extern "C" {
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
#include <libswscale/swscale.h>
}

这些头文件包含了FFmpeg库提供的函数和数据结构的声明。通过添加这些头文件的包含语句，您可以正确地使用这些函数。

重新编译您的项目，看看是否仍然存在相同的错误。如果问题仍然存在，请确保您已正确安装FFmpeg库，并检查您的代码中是否有其他引用FFmpeg函数的地方。

如果问题仍然存在，请提供更多关于您的编译环境和代码的详细信息，以便更好地帮助您解决问题。