hey guys, im kind of new in c and i have two questions, first what is the void * v[] for? second what is the "comp" in this line? "int (*comp)(void *,void *);" its part of an example program for qsort...is it casting of some kind?
appreciate any help.
1) It is an array of pointers that point to a void (can point to anything). So v[1] is a pointer, v[3] is also a pointer (a *void)
2) It is a function pointer that points to a function that is like int fun(void *, void* )
Example:
Code:int fun(void* a, void* b) { ... return 0; } int (*comp)(void*, void*); comp = &fun; //comp will point to fun comp(a, b); //like fun(a,b)
comp is a pointer to a function returning int
v is an array of void pointers
Code:printf("%c%c%c%c%c%c%c",0x68,0x68^0xd,0x68|0x4,0x68|0x4,0x68|0xf,0x68^0x49,0x68^0x62);
"int (*comp)(void *,void *);" is a function pointer. One use for that is so you can include a function as a parameter to another function:
I've never used C's qsort but apparently you can pass it your own comparison function, which accepts two pointers (to the things to compare) and returns an int.Code:#include <stdio.h> void one() { printf("Function one\n"); } void two() { printf("Function two\n"); } void dowhat (void (somefunction)()) { somefunction(); } int main() { dowhat(one); dowhat(two); return 0; }
C programming resources:
GNU C Function and Macro Index -- glibc reference manual
The C Book -- nice online learner guide
Current ISO draft standard
CCAN -- new CPAN like open source library repository
3 (different) GNU debugger tutorials: #1 -- #2 -- #3
cpwiki -- our wiki on sourceforge
