How to generate a new function in C? - c

Question

I want a function that could take input a single integer from the user with validation, lets call it input_single_int. Such a function would greatly simplify my code. If a user gives incorrect input, then the function should show error and again prompt the user to fill out the correct input. The problem is the validation part, different inputs require different validation. Even if I send a validation function, how do I send the different parameters required by the validation function through input_single_int?
I want this function to be generic, so that I could use it multiple places. In the code given, if I add a parameter in input_single_int to accomodate input of variable b, I would have to change check_a function also, which I don't want to do. I also don't want to use global variables.
The only way which I could think of achieving this is through a function that could generate another function. Something like this:
func generate_check_b(int a) {
return int check_b(int b) { return (b > 0 && b < a); };
}
Is such a thing possible in C?
#define MM_SHOW 8
#define MM_QUIT 9
int input_single_int(int *var, char msg[], int exit_on_eq, int secondary_check(int val)) {
int inp_status, error, temp;
char skip;
do {
error = 0;
printf("%s", msg);
inp_status = scanf("%d", &temp);
if (inp_status != 1) {
error = 1;
do {
scanf("%c", &skip);
if (exit_on_eq) {
if (skip == 'e') {
system("clear");
return MM_SHOW;
} else if (skip == 'q') {
system("clear");
return MM_QUIT;
}
}
} while (skip != '\n');
}
if (!secondary_check(temp)) {
error = 1;
}
} while (error && printf("Please give a correct input.\n"));
*var = temp;
return 0;
}
int check_a(int a) { return a > 0;}
int check_b(int b, int a) { return (b > 0 && b < a);}
int main() {
int a, b;
char amsg[] = "a should be more than 0: ";
char bmsg[] = "b should be more than 0 and less than a: ";
input_single_int(&a, amsg, 1, check_a);
input_single_int(&b, bmsg, 1, check_b);
return 0;
}

Answer 1

A common idiom is a pair of parameters; a function and an opaque context pointer; so a simple case could be something like:
int check_range(int a, void *p) {
int *range = p;
return a >= range[0] && a < range[1];
}
struct Set { int n; int *vals; };
int check_set(int b, void *p) {
struct Set *s = p;
int i;
for (i = 0; i < s->n && s->vals[i] != b; i++) {}
return i < s->n;
}
If you look at the blocks extension to C supported by clang & gcc, it isn't far different from this, except that it is more sugary and has some really scary side effects.