Question

我有一个来自相机制造商的库，并且在提供的演示代码中，一个名为metadata_init（）的函数工作正常，但在我的代码中，我得到一个未定义的引用错误。

演示代码的make输出：

11:33:23 **** Build of configuration Camera-R4-Debug for project Camera ****
make all 
Building file: ../src/Camera.cpp
Invoking: Cross G++ Compiler
arm-linux-gnueabihf-g++ -I/opt/Camerasdk/R4/include -I"/cameraBuilds/Wrapper/include" -I"/opt/ExternalLibraries/curl/Camera/R4/include" -I"/opt/ExternalLibraries/libxml2/Camera/R4/include" -I"/opt/ExternalLibraries/OpenCV24/Camera/R4/include" -I"/home/aro/cameraBuilds/Camera" -I/opt/InternalLibraries/include -I/opt/InternalLibraries/include_linux -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"src/Camera.d" -MT"src/Camera.o" -o "src/Camera.o" "../src/Camera.cpp"
../src/Camera.cpp: In function ‘int metadata_construct_http_message(char*, METADATA_HTTP_MESSAGE_TYPE, void*, int*)’:
../src/Camera.cpp:379:24: warning: deprecated conversion from string constant to ‘char*’ [-Wwrite-strings]
                        "</svg>\r\n";
                        ^
../src/Camera.cpp: In function ‘int main()’:
../src/Camera.cpp:426:97: warning: deprecated conversion from string constant to ‘char*’ [-Wwrite-strings]
  (void)metadata_init("stream.cgi", strlen("stream.cgi"), metadata_construct_http_message);
                                                                                                 ^
Finished building: ../src/Camera.cpp

Building file: ../src/CameraFrameGrabber.cpp
Invoking: Cross G++ Compiler
arm-linux-gnueabihf-g++ -I/opt/Camerasdk/R4/include -I"/cameraBuilds/Wrapper/include" -I"/opt/ExternalLibraries/curl/Camera/R4/include" -I"/opt/ExternalLibraries/libxml2/Camera/R4/include" -I"/opt/ExternalLibraries/OpenCV24/Camera/R4/include" -I"/home/aro/cameraBuilds/Camera" -I/opt/InternalLibraries/include -I/opt/InternalLibraries/include_linux -I/opt/InternalLibraries/ipslib/include -I/opt/InternalLibraries/ipsstream/include -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"src/CameraFrameGrabber.d" -MT"src/CameraFrameGrabber.o" -o "src/CameraFrameGrabber.o" "../src/CameraFrameGrabber.cpp"
Finished building: ../src/CameraFrameGrabber.cpp

Building file: ../src/CameraLogger.cpp
Invoking: Cross G++ Compiler
arm-linux-gnueabihf-g++ -I/opt/Camerasdk/R4/include -I"/home/aro/cameraBuilds/Wrapper/include" -I"/opt/ExternalLibraries/curl/Camera/R4/include" -I"/opt/ExternalLibraries/libxml2/Camera/R4/include" -I"/opt/ExternalLibraries/OpenCV24/Camera/R4/include" -I"/home/aro/cameraBuilds/Camera" -I/opt/InternalLibraries/include -I/opt/InternalLibraries/include_linux -I/opt/InternalLibraries/ipslib/include -I/opt/InternalLibraries/ipsstream/include -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"src/CameraLogger.d" -MT"src/CameraLogger.o" -o "src/CameraLogger.o" "../src/CameraLogger.cpp"
Finished building: ../src/CameraLogger.cpp

Building file: ../src/CameraParameter.cpp
Invoking: Cross G++ Compiler
arm-linux-gnueabihf-g++ -I/opt/Camerasdk/R4/include -I"/home/aro/cameraBuilds/Wrapper/include" -I"/opt/ExternalLibraries/curl/Camera/R4/include" -I"/opt/ExternalLibraries/libxml2/Camera/R4/include" -I"/opt/ExternalLibraries/OpenCV24/Camera/R4/include" -I"/home/aro/cameraBuilds/Camera" -I/opt/InternalLibraries/include -I/opt/InternalLibraries/include_linux -I/opt/InternalLibraries/ipslib/include -I/opt/InternalLibraries/ipsstream/include -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"src/CameraParameter.d" -MT"src/CameraParameter.o" -o "src/CameraParameter.o" "../src/CameraParameter.cpp"
Finished building: ../src/CameraParameter.cpp

Building target: Camera
Invoking: Cross G++ Linker
arm-linux-gnueabihf-g++ -L/opt/Camerasdk/R4/lib -L"/cameraBuilds/Wrapper/Camera-R4-Debug" -L"/opt/ExternalLibraries/curl/Camera/R4/lib" -L"/opt/ExternalLibraries/libxml2/Camera/R4/lib" -L"/opt/ExternalLibraries/OpenCV24/Camera/R4/lib" -L"/opt/DetectionModules/Camera/R4/lib" -L/home/aro/Downloads -o "Camera"  ./src/Camera.o ./src/CameraFrameGrabber.o ./src/CameraLogger.o ./src/CameraParameter.o   -lWrapper -lxml2 -lopencv_highgui -lopencv_imgproc -lopencv_core -lpthread -lyuvlib -lrt -llibjasper -llibjpeg -llibpng -llibtiff -lzlib -lcurl
./src/Camera.o: In function `main':
/home/aro/cameraBuilds/Camera/Camera-R4-Debug/../src/Camera.cpp:426: undefined reference to `metadata_init(char*, int, int (*)(char*, METADATA_HTTP_MESSAGE_TYPE, void*, int*))'
collect2: error: ld returned 1 exit status
make: *** [Camera] Error 1

11:33:24 Build Finished (took 1s.212ms)

就是这样，构建成功了，我将在那里有一个有效的./hicore应用程序。

我的项目有点复杂，我使用eclipse进行编译。控制台输出是：

#ifndef _HIK_METADATA_H_
#define _HIK_METADATA_H_

const int max_http_body_len = 100 * 1024;

typedef enum
{
    CMD_ADD_TYPE = 1,
    CMD_OTHER,
} METADATA_CTRL_TYPE;

typedef struct
{
    int length;
    int fd;
    METADATA_CTRL_TYPE cmd_type;
} METADATA_HEADER;

typedef struct
{
    char option[128];
    int  share_socket;
} METADATA_ADD_CFG;

typedef enum
{
    HTTP_HEADER_TYPE = 1,
    HTTP_BODY_TYPE,
} METADATA_HTTP_MESSAGE_TYPE;

typedef struct
{
    char boundary[64];
    char http_content_type[64];
    char multipart_content_type[64];
} METADATA_MULTIPART_TYPE;


typedef int (*p_metadata_construct_http_msg_callback_f)(char *p_option, METADATA_HTTP_MESSAGE_TYPE cmd_type, void *p_data, int *p_data_len);

int metadata_init(char *p_metadata_url, int url_len, p_metadata_construct_http_msg_callback_f p_callback_f);

#endif

代码本身就是一样的东西，我只是把它复制过来。

Metadata.h：

#include "Metadata.h"    
int metadata_construct_http_message(char *p_option, METADATA_HTTP_MESSAGE_TYPE cmd_type, void *p_data, int *p_data_len)
    {
        // Removed for SO
        return 0;
    }

    int main()
    {
        (void)metadata_init("stream.cgi", strlen("stream.cgi"), metadata_construct_http_message);
    ...
    }

在Camera.cpp中：

{{1}}

是什么导致这种情况，如何调试此问题以缩小解决方法？

Answer 1

它认为问题可能是metadata_init是一个C函数，但是你从C ++代码中使用它。

如果是这种情况，必须在头文件中使用extern "C"，如下所示：

#ifdef  __cplusplus
extern "C" {
#endif

// embed the whole contents of the header file here, I just put the function here for brevity

int metadata_init(char *p_metadata_url, int url_len, p_metadata_construct_http_msg_callback_f p_callback_f);

#ifdef  __cplusplus
}
#endif

这是因为名称修改规则。 C和C ++中的名称不同。使用extern "C"，您告诉编译器里面的名称应该与“C”mangling一起使用。

与C相比，C ++必须进行复杂的名称修改，因为它必须将几乎所有签名信息嵌入到名称（所有参数类型）中，而在C中，受损名称通常与函数名称相同，或者有一个_前置。

未定义的引用（但nm表示函数存在）

1 个答案: