库已链接，但引用未定义 [英] library is linked but reference is undefined

问题描述

我试图在Ubuntu上编译一个openCL程序，使用之前工作过的NVIDIA卡，

  #include< ; CL / cl.h> 
 #include< iostream> 
 #include< vector> 
 
 using namespace std; 
 
 int main（）{
 cl_platform_id platform; 
 cl_device_id device; 
 cl_context context; 
 cl_command_queue command_queue; 
 cl_int error; 
 
 if（clGetPlatformIDs（1，& platform，NULL）！= CL_SUCCESS）{
 cout< 平台错误< endl; 
} 
 
 if（clGetDeviceIDs（platform，CL_DEVICE_TYPE_GPU，1，& device，NULL）！= CL_SUCCESS）{
 cout< 设备错误< endl; 
} 
 
 context = clCreateContext（NULL，1，& device，NULL，NULL，& error）; 
 if（error！= CL_SUCCESS）{
 cout<< 上下文错误< endl; 
} 
 
 command_queue = clCreateCommandQueue（context，device，0，& error）; 
 if（error！= CL_SUCCESS）{
 cout<< 命令队列错误< endl; 
} 
 
 return 0; 
} 
  

我这样编译，

  G ++ -I在/ usr /本地/ CUDA /包括-L / usr / lib目录/ NVIDIA电流-lOpenCL opencl.cpp 
  
 
 
 
我得到这个结果
  / tmp /ccAdS9ig.o：在函数'主'：
 opencl.cpp :(文字+ 0X1A）：未定义的参考`clGetPlatformIDs'
 opencl.cpp :(文字+ 0x3D之间）：未定义参考`clGetDeviceIDs'。
 opencl.cpp :(文字+ 0x65）中：未定义引用`clCreateContext'
 opencl.cpp :(文字+ 0x85未）：未定义的参考`clCreateCommandQueue'
 collect2 ：ld返回1退出状态
  
但 nm -D / usr / lib / NVIDIA电流/ libOpenCL.so 告诉我，libOpenCL.so至少包含clGetPlatformIDs 
  0000000000002400Ť clGetKernelWorkGroupInfo 
 0000000000002140牛逼clGetMemObjectInfo 
 0000000000002e80牛逼clGetPlatformIDs 
 0000000000002de0牛逼clGetPlatformInfo 
 0000000000002310牛逼clGetProgramBuildInfo 
 00000000000022f0牛逼clGetProgramInfo 
 00000000000021f0牛逼clGetSamplerInfo 
  
我失去了一些东西。
 
 
解决方案
 
从 gcc 手册页：
  -llibrary 
 -l库
链接时搜索名为库的库。 （与库作为一个单独的参数的第二个选择是仅适用于符合POSIX标准，不建议使用。）
 
这使得其中的命令，你写这个选项是有所不同;链接器搜索和处理库和目标文件中它们被指定的顺序。因此，foo.o 
 -lz bar.o在文件foo.o之后但在bar.o之前搜索库z。如果bar.o引用z中的函数，那些函数可能无法加载。 
 
链接器搜索库的标准目录列表，实际上是一个名为liblibrary.a的文件。链接器然后使用此文件，就好像它已经通过名称指定了
。 
  
所以尝试指定 -lOpenCL 您的编译命令中的文件参数。
 
 
 
您还在libOpenCL.so中搜索符号，这是一个共享库文件。用你的命令你的程序再次链接一个静态库，格式 libOpenCL.a 。
 
I'm trying to compile an openCL program on Ubuntu with an NVIDIA card that worked once before,
#include <CL/cl.h>
#include <iostream>
#include <vector>

using namespace std;

int main() {
  cl_platform_id platform;
  cl_device_id device;
  cl_context context;
  cl_command_queue command_queue;
  cl_int error;

  if(clGetPlatformIDs(1, &platform, NULL) != CL_SUCCESS) {
    cout << "platform error" << endl;
  }

  if(clGetDeviceIDs(platform, CL_DEVICE_TYPE_GPU, 1, &device, NULL) != CL_SUCCESS) {
    cout << "device error" << endl;
  }

  context = clCreateContext(NULL, 1, &device, NULL, NULL, &error);
  if(error != CL_SUCCESS) {
    cout << "context error" << endl;
  }

  command_queue = clCreateCommandQueue(context, device, 0, &error);
  if(error != CL_SUCCESS) {
    cout << "command queue error" << endl;
  }

  return 0;
}
I compile it like so,
g++ -I/usr/local/cuda/include -L/usr/lib/nvidia-current -lOpenCL opencl.cpp
and I get this result
/tmp/ccAdS9ig.o: In function `main':
opencl.cpp:(.text+0x1a): undefined reference to `clGetPlatformIDs'
opencl.cpp:(.text+0x3d): undefined reference to `clGetDeviceIDs'
opencl.cpp:(.text+0x65): undefined reference to `clCreateContext'
opencl.cpp:(.text+0x85): undefined reference to `clCreateCommandQueue'
collect2: ld returned 1 exit status
but nm -D /usr/lib/nvidia-current/libOpenCL.so tells me that libOpenCL.so at least contains clGetPlatformIDs
0000000000002400 T clGetKernelWorkGroupInfo
0000000000002140 T clGetMemObjectInfo
0000000000002e80 T clGetPlatformIDs
0000000000002de0 T clGetPlatformInfo
0000000000002310 T clGetProgramBuildInfo
00000000000022f0 T clGetProgramInfo
00000000000021f0 T clGetSamplerInfo
Am I missing something.
解决方案
From the gcc man page:
   -llibrary
   -l library
       Search the library named library when linking.  (The second alternative with the library as a separate argument is only for POSIX compliance and is not recommended.)

       It makes a difference where in the command you write this option; the linker searches and processes libraries and object files in the order they are specified.  Thus, foo.o
       -lz bar.o searches library z after file foo.o but before bar.o.  If bar.o refers to functions in z, those functions may not be loaded.

       The linker searches a standard list of directories for the library, which is actually a file named liblibrary.a.  The linker then uses this file as if it had been specified
       precisely by name.
So try to specify the -lOpenCL after the file argument in your compile command.

You also search for symbols in libOpenCL.so, which is a shared library file. With your command you link your program agains a static library, in the format libOpenCL.a.

                        
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