Memory usage across functions

1.To modify the value of a real parameter through a function without a return value, the address must be passed.

Void f (int * p)

{

* P = 100;

}

Int main ()

{

Int a = 9;

F (& a); // No matter what type of variable, the address must be passed here to modify its value through the function. P = & a, then * p is equivalent to

Printf ("a = % d \ n", );

Return0;

}

2.Memory usage across functions

Question: In the next program, we can call the function fun to point the pointer Variable p in the main function to a valid integer unit.

A main ()

{

Int * p;

Fun (p); // the address of p is not passed here, so it must be wrong.

...

}

Int fun (int * q)

{

Int s;

Q = & s;

}

B main ()

{

Int * p;

Fun (& p );

...

}

Int fun (int ** q)

{

Int s;

* Q = & s;

}

// It seems correct, but it is actually incorrect. If the p address is passed to q, * q is equivalent to p, p points to s, but the variable s is valid only within the fun function. After the fun function is executed, s memory is released, not a legal integer unit

C main ()

{

Int * p;

Fun (& p );

...

}

Int fun (int ** q)

{

* Q = (int *) malloc (sizeof (int); // correct. The memory allocated by malloc must be automatically released by free.

}

D main ()

{

Int * p;

Fun (p); // No address is added for direct error judgment

...

}

Int fun (int * q)

{

Q = (int *) malloc (sizeof (int ));

}