Update global variable in C via reference by parameter

问题

short int PC = 0;

int main() {
    foo(&PC) ;
}

void foo(short int PC) {
    PC++;
}

How do I successfully update the global variable of PC?

Note: PC must be passed as a parameter and the global variable needs to be modified via the parameter.

As you can tell I am new to C and am trying to understand the difference between * and &. Any help would be much appreciated.

回答1:

You just need to take the argument as a pointer:

short int PC = 0;

void foo(short int *pc) {
    (*pc)++;
}

int main() {
    foo(&PC) ;
}

I moved foo() above main() because in C you have to declare things before they are used. If you prefer you could forward declare it by saying void foo(); at the top and leave the definition below.

来源：https://stackoverflow.com/questions/39715740/update-global-variable-in-c-via-reference-by-parameter