Can someone explain what does this mean?

Question

While browsing the sqlite documentation for C I've found this as a parameter to a function, what does it mean?

int (*callback)(void*,int,char**,char**);

Answer 1

This is the prototype of a function pointer to a callback function.

Because it is used as an argument in another function, it implies that that actual function needs to be declared and defined somewhere in your code before it is used in the function as an argument. I.e. something like this:

//declaration - possibly defined in a header file, or at top of .c file where it is used
int __cdecl handlerFunction(void*,int,char**,char**); 

//definition 
int __cdecl handlerFunction(void *db,int element,char **data1,char **data2)
{
    //code to handle some event that invokes this callback
    return 0
}