use qsort with comparator function

Question

i know qsort from c library and i have implemented it with chars and integers(convert from const void * form to relevant form) but now i am implementing code which gives me longest duplicated in given sentences here is simple compare function

int pstrcmp(char **p,char **q){
    return strcmp(*p,*q);

}

and i want to use it in qsort like this

qsort(a,n,sizeof(char *),pstrcmp);(a is array of strings)

when i write directly,it writes it is incompatible and son on,shows me error,please help me to correct it

error is this

2 IntelliSense: argument of type "int (*)(char **p, char **q)" is incompatible with parameter of type "int (__cdecl *)(const void *, const void *)" c:\users\datuashvili\documents\visual studio 2010\projects\duplicate_strings\duplicate_strings\duplicates_strings.cpp 32 27 duplicate_strings

Answer 1

You need to give your comparator function the correct function signature and then cast internally, e.g.

int pstrcmp(const void * p, const void * q)
{
    const char **ps = (const char **)p;
    const char **qs = (const char **)q;

    return strcmp(*ps, *qs);
}