digitalmars.D.learn - How to pass delegates to C functions?
- Jeroen Bollen (7/7) Apr 03 2014 After being downvoted on stackoverflow for no apperant reason, I
- Justin Whear (4/12) Apr 03 2014 c-functions-in-d
- Jeroen Bollen (2/18) Apr 03 2014 It will get called.
- Adam D. Ruppe (40/42) Apr 03 2014 You can't do it directly in general, unless you can modify the C
- Jeroen Bollen (2/44) Apr 03 2014 Thanks.
- Mengu (2/9) Apr 03 2014 OT: you've got another upvote!
- Jeroen Bollen (3/14) Apr 03 2014 Ever since I posted it here it started climbing back up the
After being downvoted on stackoverflow for no apperant reason, I figured I'd give it a shot here. How do I pass a delegate to an external C function taking a function pointer? If you want some extra rep on StackOverflow you can also answer here: http://stackoverflow.com/questions/22845175/pass-delegates-to-external-c-functions-in-d
Apr 03 2014
On Thu, 03 Apr 2014 17:59:30 +0000, Jeroen Bollen wrote:After being downvoted on stackoverflow for no apperant reason, I figured I'd give it a shot here. How do I pass a delegate to an external C function taking a function pointer? If you want some extra rep on StackOverflow you can also answer here: http://stackoverflow.com/questions/22845175/pass-delegates-to-external-c-functions-in-d Does the C function use the function pointer (call it), or just pass it around/store it?
Apr 03 2014
"Jeroen Bollen" <jbinero gmail.com> On Thursday, 3 April 2014 at 18:05:26 UTC, Justin Whear wrote:On Thu, 03 Apr 2014 17:59:30 +0000, Jeroen Bollen wrote:It will get called.After being downvoted on stackoverflow for no apperant reason, I figured I'd give it a shot here. How do I pass a delegate to an external C function taking a function pointer? If you want some extra rep on StackOverflow you can also answer here: http://stackoverflow.com/questions/22845175/pass-delegates-to-external-c-functions-in-d Does the C function use the function pointer (call it), or just pass it around/store it?
Apr 03 2014
On Thursday, 3 April 2014 at 17:59:33 UTC, Jeroen Bollen wrote:How do I pass a delegate to an external C function taking a function pointer?You can't do it directly in general, unless you can modify the C function, then you can hack around it, but a delegate and a regular function pointer are pretty different animals. But perhaps you can magic hack it. Observe: // a C function that needs a plain function extern(C) void test(void function() f) { // pretend this impl is in C f(); } // just create a random delegate void delegate() foo(int a) { return { import std.stdio; writeln(a); }; } // what we want to work void main() { auto dg = foo(10); dg(); // works //test(dg); // won't work test(bindDelegate(dg)); // we want this } // transform delegate into pointer.. import std.traits; auto bindDelegate(T, string file = __FILE__, size_t line = __LINE__)(T t) if(isDelegate!T) { static T dg; dg = t; extern(C) static ReturnType!T func(ParameterTypeTuple!T args) { return dg(args); } return &func; } What bindDelegate does is create a special static variable and function for that specific call. It is as if we wrote a separate function and global to hold it. The __FILE__, __LINE__ things are a filthy hack to make it instantitate a separate variable+function pair for different lines so the global variable holding the delegate won't be so easily overwritten.
Apr 03 2014
On Thursday, 3 April 2014 at 18:13:31 UTC, Adam D. Ruppe wrote:On Thursday, 3 April 2014 at 17:59:33 UTC, Jeroen Bollen wrote:Thanks.How do I pass a delegate to an external C function taking a function pointer?You can't do it directly in general, unless you can modify the C function, then you can hack around it, but a delegate and a regular function pointer are pretty different animals. But perhaps you can magic hack it. Observe: // a C function that needs a plain function extern(C) void test(void function() f) { // pretend this impl is in C f(); } // just create a random delegate void delegate() foo(int a) { return { import std.stdio; writeln(a); }; } // what we want to work void main() { auto dg = foo(10); dg(); // works //test(dg); // won't work test(bindDelegate(dg)); // we want this } // transform delegate into pointer.. import std.traits; auto bindDelegate(T, string file = __FILE__, size_t line = __LINE__)(T t) if(isDelegate!T) { static T dg; dg = t; extern(C) static ReturnType!T func(ParameterTypeTuple!T args) { return dg(args); } return &func; } What bindDelegate does is create a special static variable and function for that specific call. It is as if we wrote a separate function and global to hold it. The __FILE__, __LINE__ things are a filthy hack to make it instantitate a separate variable+function pair for different lines so the global variable holding the delegate won't be so easily overwritten.
Apr 03 2014
On Thursday, 3 April 2014 at 17:59:33 UTC, Jeroen Bollen wrote:After being downvoted on stackoverflow for no apperant reason, I figured I'd give it a shot here. How do I pass a delegate to an external C function taking a function pointer? If you want some extra rep on StackOverflow you can also answer here: http://stackoverflow.com/questions/22845175/pass-delegates-to-external-c-functions-in-dOT: you've got another upvote!
Apr 03 2014
On Friday, 4 April 2014 at 05:20:42 UTC, Mengu wrote:On Thursday, 3 April 2014 at 17:59:33 UTC, Jeroen Bollen wrote:Ever since I posted it here it started climbing back up the ladder. Doesn't really matter now anyways, I got my answer. :PAfter being downvoted on stackoverflow for no apperant reason, I figured I'd give it a shot here. How do I pass a delegate to an external C function taking a function pointer? If you want some extra rep on StackOverflow you can also answer here: http://stackoverflow.com/questions/22845175/pass-delegates-to-external-c-functions-in-dOT: you've got another upvote!
Apr 03 2014