CODEWITHSUNDEEP
cpointerscasting
Paulo Gasol
Paulo Gasol

Reputation: 83

Complex definition in C

Because I have been confused, Can someone explain me what *(int*)a or *(int*)b is in the following example, type casting or some complex pointer declaration? I need to use bsearch function. Thanks

int cmpfunc(const void * a, const void * b)
{
   return ( *(int*)a - *(int*)b );
}

Upvotes: 0

Views: 448

Answers (2)

ensc
ensc

Reputation: 6994

A more readable version without explicit (and potentially unsafe) casts would be

int cmpfunc(const void * a_, const void * b_)
{
    int const *a = a_;
    int const *b = b_;

    return *a - *b;
}

Upvotes: 0

dbush
dbush

Reputation: 224437

This is a cast. a, which is of type const void *, is first cast to an int *, then that int * is dereferenced to read an int.

Breaking it down:

  • a: type const void *
  • (int *)a: type int *
  • *(int *)a: type int.

The reason this is done is because a function of type int (*)(const void *, const void *) is required to be passed to the bsearch and qsort functions as a callback. Defining the arguments as const void * allows qsort to sort any arbitrary data by having the callback function cast the arguments to the appropriate type.

Upvotes: 3

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