Warning when using qsort in C
I wrote开发者_StackOverflow社区 my comparison function
int cmp(const int * a,const int * b)
{
if (*a==*b)
return 0;
else
if (*a < *b)
return -1;
else
return 1;
}
and i have my declaration
int cmp (const int * value1,const int * value2);
and I'm calling qsort in my program like so
qsort(currentCases,round,sizeof(int),cmp);
when i compile it I get the following warning
warning: passing argument 4 of ‘qsort’ from incompatible pointer type
/usr/include/stdlib.h:710: note: expected ‘__compar_fn_t’ but argument is of type ‘int
(*)(const int *, const int *)’
The program works just fine so my only concern is why it doesn't like the way im using that?
The cmp
function's prototype must be
int cmp(const void* a, const void* b);
You can either cast it in the invocation of qsort (not recommended):
qsort(currentCases, round, sizeof(int), (int(*)(const void*,const void*))cmp);
or casts the void-pointers to int-pointers in cmp (the standard approach):
int cmp(const void* pa, const void* pb) {
int a = *(const int*)pa;
int b = *(const int*)pb;
...
According to the man page, a __compar_fn_t
is defined as: typedef int(*) __compar_fn_t (const void *, const void *)
Your cmp
specifies int*
parameters. It doesn't like that, but is only listed as a warning.
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