C Language: TypeDef definition function pointer __ function

In the use of TypeDef, the most troublesome point is the pointer to a function, and without the following function, you know the definition of the expression below and how to use it.   Int (*s_calc_func (char op)) (int, int); If you do not know, please see the following program, which has a more detailed description #include <stdio.h>//Declaration four functions
int add (int, int);
int sub (int, int);
int mul (int, int);
int div (int, int); To define a pointer to this type of function
typedef int (*FP_CALC) (int, int); Int (*s_calc_func (char op)) (int, int);
Int (*s_calc_func (char op)) (int, int); and Fp_calc Calc_func (char op);
Defines a function calc_func, which returns a pointer to the corresponding calculation function, based on the action character op
Fp_calc Calc_func (char op); Returns the corresponding calculated value based on the OP
int calc (int A, int b, char op);
int add (int a, int b)
{
return a + B;
int sub (int a, int b)
{
return a-b;
int mul (int a, int b)
{
return a * b;
int div (int a, int b)
{
Return b? A/b:-1;
The purpose of this function is exactly the same as the next function job and invocation method, with the OP instead of the last two cosmetic
Int (*s_calc_func (char op)) (int, int)
{
Return Calc_func (OP);
} Fp_calc Calc_func (char op)
{
Switch (OP)
{
Case ' + ': return add;
Case '-': return sub;
Case ' * ': return mul;
Case '/': return div;

Default
return NULL;
}
return NULL;
int calc (int A, int b, char op)
{
Fp_calc fp = calc_func (OP); Here is a similar direct definition pointing to a function pointer variable

The following line is an example of a pointer to a function without a typedef, trouble.
Int (*S_FP) (int, int) = S_calc_func (OP);

ASSERT (fp = = S_FP); You can assert that these two are equal.

if (FP)
Return FP (A, b);
Else
return-1;
} void Main ()
{
int a = m, B = 20;

printf ("Calc (%d,%d,%c) =%d/n", A, B, ' + ', calc (A, B, ' + '));
printf ("Calc (%d,%d,%c) =%d/n", A, B, '-', Calc (A, B, '-'));
printf ("Calc (%d,%d,%c) =%d/n", A, B, ' * ', Calc (A, B, ' * '));
printf ("Calc (%d,%d,%c) =%d/n", A, B, '/', Calc (A, B, '/'));
Run Result: Calc (+, +) = Calc (m,-) = Calc (m, *) = Calc (100, 20,/) = 5