错误：从'void *'到'int（*）（const void *，const void *）'的无效转换

Question

While compiling my C file, I am getting the below error:

error: invalid conversion from 'void*' to 'int (*)(const void*, const void*)'
error:   initializing argument 1 of 'void* bsearch(int (*)(const void*, const void*))'

Below are some code snippets:

static int
testfucn(const char *func, const teststruct *array)
{
  return (strcmp(func, array->name));
}

int
test(char *fcn)
{
    if (bsearch((void*)testfucn))
        return(1);
    else
        return(0);
}

Error is coming for the line bsearch((void*)testfucn)

Could you please suggest what is wrong with this code and how to resolve this issue.

Answer 1

The error is pretty explicit - you're passing in a void* (obtained by your explicit cast) while the function expects an int (*)(const void*, const void*) . There is no implicit conversion from 'pointer to void ' to 'pointer to a function', hence the error.

I believe you could get away with casting the function to the requested type:

bsearch((int (*)(const void*, const void*)testfucn);

However, note that while it might (appear to) work in practice, it would invoke Undefined Behaviour.

The correct, type-safe solution is to actually declare a function with the appropriate signature, possibly as a wrapper around your real function:

static int
testfucn_for_bsearch(const void *func, const void *array)
{
  return testfucn(func, array);
}

/* ... */

bsearch(testfucn_for_bsearch);

Answer 2

Remove the cast. You can't cast between data ( void * ) and function pointers, and the argument should be a function pointer.

Also fix your function's signature, it doesn't match the expected signature of a bsearch() callback. See the manual page for the proper signature.