Qsort array of structs compare function

Question

Okay, I got this to work by looking around online and such, but can someone explain what lines numbered 1 and 2 do exactly and why they are needed

int structCompare(const void *a, const void *b)
{
     struct trade *tempA = (struct trade *)a;//(1)
     struct trade *tempB = (struct trade *)b;//(2)
     return strcmp(tempA->name, tempB->name);
}

cnicutar · Accepted Answer · 2012-05-25 19:44:08Z

3

Those lines cast the generic void pointers to struct trade pointers. The explicit cast is superfluous in C when void * is involved and should be eliminated:

 struct trade *tempA = a;
 struct trade *tempB = b;
 return strcmp(tempA->name, tempB->name);

You could have written:

return strcmp(((struct trade *)a)->name, ((struct trade *)b)->name);

I prefer the first one though.

answered May 25, 2012 at 19:44

cnicutar

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1 Comment

Andrew Over a year ago

Ohh, thank you. Seeing them not casted makes more sense. Also, thanks for the simplified version. Actually I have multiple layers of sorting in case the name field is the same, but I'll keep your one line solution in mind!

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