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Currently I'm creating some sort of plugin system. My program writes the code, which is then compiled (see also my other question). The resulting (compiled) library is than opened again using dlopen. This allows people to program custom functions in the program themselves.

//Open the compiled library at the specified path
void* handle = dlopen("COMPILEDLIBRARYPATH", RTLD_LAZY);
if (handle == NULL) 
 std::cout << "plugin not found" << std::endl;


//Find the function pointer and cast is to std::function (is this good practice??)
std::function<void(float[])> fun = (void (*)(float[]))dlsym(handle, "testFunc");
if (fun == NULL) 
 std::cout << "function not found" << std::endl;


float test[3] = 0.0, 0.0, 0.0;
std::cout << "calling plugin" << std::endl;
fun(test);

//Output the result of the call
std::cout << test[0] << " " << test[1] << " " << test[2] << " returned by function" << std::endl;

//Close handle again
if (dlclose(handle) != 0) 
 std::cout << "could not close function" << std::endl;

This works as expected, but also feels sort of hacky and unsafe. I've never done anything like this before, so am I doing anything unsafe here? Also, is there a "better" way to do this (e.g. where I don't have to manage closing the handle again)? Could this be considered portable across OSes?

c++ shared-libraries dlopen

share|improve this question

edited Mar 28 at 9:27

Mike Kinghan

35.4k88 gold badges7979 silver badges125125 bronze badges

asked Mar 28 at 9:02

me meme me

10611 gold badge11 silver badge1010 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  You could use a std::unique_ptr with a custom deleter to avoid closing explicitly.
  
  – Aconcagua
  Mar 28 at 9:12
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  std::function comes with some overhead; if the type of the function is clear right from the start, I'd rather prefer a raw function pointer instead. As you have the cast anyway, you might let deduce the type by auto. And you should prefer C++ keywords (nullptr) over old (obsolete?) C macros (NULL).
  
  – Aconcagua
  Mar 28 at 9:16
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  About naming: I'd give the function pointer the same name as the function in the dll.
  
  – Aconcagua
  Mar 28 at 9:17
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Hm, if it works as expected, maybe better suited for codereview.stackexchange.com?
  
  – Aconcagua
  Mar 28 at 9:29
  

  
  
  
  

add a comment | 

0

Currently I'm creating some sort of plugin system. My program writes the code, which is then compiled (see also my other question). The resulting (compiled) library is than opened again using dlopen. This allows people to program custom functions in the program themselves.

//Open the compiled library at the specified path
void* handle = dlopen("COMPILEDLIBRARYPATH", RTLD_LAZY);
if (handle == NULL) 
 std::cout << "plugin not found" << std::endl;


//Find the function pointer and cast is to std::function (is this good practice??)
std::function<void(float[])> fun = (void (*)(float[]))dlsym(handle, "testFunc");
if (fun == NULL) 
 std::cout << "function not found" << std::endl;


float test[3] = 0.0, 0.0, 0.0;
std::cout << "calling plugin" << std::endl;
fun(test);

//Output the result of the call
std::cout << test[0] << " " << test[1] << " " << test[2] << " returned by function" << std::endl;

//Close handle again
if (dlclose(handle) != 0) 
 std::cout << "could not close function" << std::endl;

This works as expected, but also feels sort of hacky and unsafe. I've never done anything like this before, so am I doing anything unsafe here? Also, is there a "better" way to do this (e.g. where I don't have to manage closing the handle again)? Could this be considered portable across OSes?

c++ shared-libraries dlopen

share|improve this question

edited Mar 28 at 9:27

Mike Kinghan

35.4k88 gold badges7979 silver badges125125 bronze badges

asked Mar 28 at 9:02

me meme me

10611 gold badge11 silver badge1010 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  You could use a std::unique_ptr with a custom deleter to avoid closing explicitly.
  
  – Aconcagua
  Mar 28 at 9:12
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  std::function comes with some overhead; if the type of the function is clear right from the start, I'd rather prefer a raw function pointer instead. As you have the cast anyway, you might let deduce the type by auto. And you should prefer C++ keywords (nullptr) over old (obsolete?) C macros (NULL).
  
  – Aconcagua
  Mar 28 at 9:16
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  About naming: I'd give the function pointer the same name as the function in the dll.
  
  – Aconcagua
  Mar 28 at 9:17
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Hm, if it works as expected, maybe better suited for codereview.stackexchange.com?
  
  – Aconcagua
  Mar 28 at 9:29
  

  
  
  
  

add a comment | 

Currently I'm creating some sort of plugin system. My program writes the code, which is then compiled (see also my other question). The resulting (compiled) library is than opened again using dlopen. This allows people to program custom functions in the program themselves.

//Open the compiled library at the specified path
void* handle = dlopen("COMPILEDLIBRARYPATH", RTLD_LAZY);
if (handle == NULL) 
 std::cout << "plugin not found" << std::endl;


//Find the function pointer and cast is to std::function (is this good practice??)
std::function<void(float[])> fun = (void (*)(float[]))dlsym(handle, "testFunc");
if (fun == NULL) 
 std::cout << "function not found" << std::endl;


float test[3] = 0.0, 0.0, 0.0;
std::cout << "calling plugin" << std::endl;
fun(test);

//Output the result of the call
std::cout << test[0] << " " << test[1] << " " << test[2] << " returned by function" << std::endl;

//Close handle again
if (dlclose(handle) != 0) 
 std::cout << "could not close function" << std::endl;

This works as expected, but also feels sort of hacky and unsafe. I've never done anything like this before, so am I doing anything unsafe here? Also, is there a "better" way to do this (e.g. where I don't have to manage closing the handle again)? Could this be considered portable across OSes?

c++ shared-libraries dlopen

share|improve this question

edited Mar 28 at 9:27

Mike Kinghan

35.4k88 gold badges7979 silver badges125125 bronze badges

asked Mar 28 at 9:02

me meme me

10611 gold badge11 silver badge1010 bronze badges

//Open the compiled library at the specified path
void* handle = dlopen("COMPILEDLIBRARYPATH", RTLD_LAZY);
if (handle == NULL) 
 std::cout << "plugin not found" << std::endl;


//Find the function pointer and cast is to std::function (is this good practice??)
std::function<void(float[])> fun = (void (*)(float[]))dlsym(handle, "testFunc");
if (fun == NULL) 
 std::cout << "function not found" << std::endl;


float test[3] = 0.0, 0.0, 0.0;
std::cout << "calling plugin" << std::endl;
fun(test);

//Output the result of the call
std::cout << test[0] << " " << test[1] << " " << test[2] << " returned by function" << std::endl;

//Close handle again
if (dlclose(handle) != 0) 
 std::cout << "could not close function" << std::endl;

share|improve this question

edited Mar 28 at 9:27

Mike Kinghan

35.4k88 gold badges7979 silver badges125125 bronze badges

asked Mar 28 at 9:02

me meme me

10611 gold badge11 silver badge1010 bronze badges

share|improve this question

edited Mar 28 at 9:27

Mike Kinghan

35.4k88 gold badges7979 silver badges125125 bronze badges

asked Mar 28 at 9:02

me meme me

10611 gold badge11 silver badge1010 bronze badges

edited Mar 28 at 9:27

Mike Kinghan

35.4k88 gold badges7979 silver badges125125 bronze badges

edited Mar 28 at 9:27

Mike Kinghan

35.4k88 gold badges7979 silver badges125125 bronze badges

asked Mar 28 at 9:02

me meme me

10611 gold badge11 silver badge1010 bronze badges

asked Mar 28 at 9:02

me meme me

10611 gold badge11 silver badge1010 bronze badges

1 Answer
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0

Theres is dlclose(void *handle) for closing a handle. Also prefer reinterpret_cast to a raw function pointer, instead of C-style casting to an std::function.

dlfcn.h with dlopen and its friends is POSIX/UNIX API, so it will probably work on Solaris, Linux, *BSD, macOS etc. On Windows the equivalent of dlysym is GetProcAddress in <windows.h>.

Here a is a full article about dynamic loading thal'll probably help: https://en.wikipedia.org/wiki/Dynamic_loading#In_C/C++

share|improve this answer

answered Mar 28 at 9:25

KorniKorni

42911 silver badge1010 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  ... and dlopen is LoadLibrary.
  
  – Aconcagua
  Mar 28 at 9:28
  

  
  
  
  

add a comment | 

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0

Theres is dlclose(void *handle) for closing a handle. Also prefer reinterpret_cast to a raw function pointer, instead of C-style casting to an std::function.

dlfcn.h with dlopen and its friends is POSIX/UNIX API, so it will probably work on Solaris, Linux, *BSD, macOS etc. On Windows the equivalent of dlysym is GetProcAddress in <windows.h>.

Here a is a full article about dynamic loading thal'll probably help: https://en.wikipedia.org/wiki/Dynamic_loading#In_C/C++

share|improve this answer

answered Mar 28 at 9:25

KorniKorni

42911 silver badge1010 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  ... and dlopen is LoadLibrary.
  
  – Aconcagua
  Mar 28 at 9:28
  

  
  
  
  

add a comment | 

0

Theres is dlclose(void *handle) for closing a handle. Also prefer reinterpret_cast to a raw function pointer, instead of C-style casting to an std::function.

dlfcn.h with dlopen and its friends is POSIX/UNIX API, so it will probably work on Solaris, Linux, *BSD, macOS etc. On Windows the equivalent of dlysym is GetProcAddress in <windows.h>.

Here a is a full article about dynamic loading thal'll probably help: https://en.wikipedia.org/wiki/Dynamic_loading#In_C/C++

share|improve this answer

answered Mar 28 at 9:25

KorniKorni

42911 silver badge1010 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  ... and dlopen is LoadLibrary.
  
  – Aconcagua
  Mar 28 at 9:28
  

  
  
  
  

add a comment | 

Theres is dlclose(void *handle) for closing a handle. Also prefer reinterpret_cast to a raw function pointer, instead of C-style casting to an std::function.

dlfcn.h with dlopen and its friends is POSIX/UNIX API, so it will probably work on Solaris, Linux, *BSD, macOS etc. On Windows the equivalent of dlysym is GetProcAddress in <windows.h>.

Here a is a full article about dynamic loading thal'll probably help: https://en.wikipedia.org/wiki/Dynamic_loading#In_C/C++

share|improve this answer

answered Mar 28 at 9:25

KorniKorni

42911 silver badge1010 bronze badges

share|improve this answer

answered Mar 28 at 9:25

KorniKorni

42911 silver badge1010 bronze badges

answered Mar 28 at 9:25

KorniKorni

42911 silver badge1010 bronze badges

answered Mar 28 at 9:25

KorniKorni

42911 silver badge1010 bronze badges