从内部if语句（C）声明全局变量

Question

I am trying to declare a variable from inside an if statement because based upon a condition, the variable will be of a different type to be used later.

uint8_t gpio_flag(PORT_t * port, uint8_t pin) {
    if(getType(port)) {     // odd
        DIO_PORT_Odd_Interruptable_Type * _port = port;
    }
    else {                  // even
        DIO_PORT_Even_Interruptable_Type * _port = port-1;
    }

    return ((_port->IFG & (1<<pin))==1);
}

Where the Odd_int_type and Even_int_type are both structs that have an IFG member. getType just returns 1 if odd and 0 if even.

However, the scope of _port is within the if statement so it doesn't work. Is there a workaround?

Trying to do this for a project I'm working on with the MSP432P401R microcontroller.

Answer 1

When you declare a variable inside the if scope, it won't be accesible outside it due to the scope limitation. Assuming you just want to point to different data depending on odd/even port, you just need to increase the scope of _port to whatever you need. If you are trying to access same memory with different variables, one way you can do it is using a union of structs. You will need to increase the scope of the variable anyway.

Answer 2

You cannot declare anything outside the current scope that isn't extern. You can declare _port variable in function, file or global scope, then set its value in your gpio_flag function. If DIO_PORT_Odd_Interruptable_Type and DIO_PORT_Even_Interruptable_Type are aliases for PORT_t, then you can simply define PORT_t _port; and track whether it is odd or even with bool _portIsEven; .