function declaration in function prototype(need help)

Question

void sortRecords(char* records[], int size, int isGreater(const char rec1[],
                                                        const char rec2[]));
int isGreaterByName(const char record1[], const char record2[]);

int isGreaterByCity(const char record1[], const char record2[]);

int isGreaterByEmail(const char record1[], const char record2[]);

Actually i dont know how to search that(even know how to call) .. I need to know how to use this type of functions.

I ve these as my function prototypes. i need a example usage for this function :)

I ve tried this

char eMail[30];
sortRecords(addresses,30,isGreaterByName(eMail,eMail));

but compiler gave me

In function 'main':|
|69|error: passing argument 3 of 'sortRecords' makes pointer from integer without a cast|
|50|note: expected 'int (*)(const char *, const char *)' but argument is of type 'int'|
||=== Build finished: 1 errors, 0 warnings (0 minutes, 0 seconds) ===|

sorry for my bad english ^.^

Answer 1

When you pass a function pointer, you omit the parentheses and arguments:

sortRecords(addresses, 30, isGreaterByName);

When you include the parentheses and arguments, the compiler calls the function and passes the return value (which is usually not a pointer to function) to the function that requires a pointer to function, leading to the problem shown.

You're using a modern version of GCC, which does its best to tell you what's wrong:

expected 'int (*)(const char *, const char *)' but argument is of type 'int'

The return value from the function is an int ; the type expected is int (*)(const char *, const char *) which is how you write a cast to a function pointer. Ultimately, you need to learn that notation.