calling qsort with a pointer to a c++ function -

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i have found book states if want use function c standard library takes function pointer argument (for example qsort), function of want pass function pointer needs c function , therefore declared extern "c".

e.g. 

extern "c" {   int foo(void const* a, void const* b) {...} }  ...  qsort(some_array, some_num, some_size, &foo);

i not surprised if wrong information, - i'm not sure, so: correct?

a lot depends on whether you're interested in practical answer compiler you're using right now, or whether care theoretical answer covers possible conforming implementations of c++. in theory it's necessary. in reality, can without it.

the real question whether compiler uses different calling convention calling global c++ function when calling c function. most compilers use same calling convention either way, call work without extern "c" declaration.

the standard doesn't guarantee though, in theory there compiler used different calling conventions two. @ least offhand, don't know of compiler that, given number of compilers around, wouldn't surprise me terribly if there 1 don't know about.

otoh, raise question: if you're using c++, why using qsort @ all? in c++, std::sort preferable -- easier use , faster well.


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