How to customize function parameter errors(c )-CodePudding

I wrote a function that requires two parameters, but I don't want those two parameters to be 0.

I want to make the compiler know that those two parameters cannot be 0 through some ways, otherwise the editor will report an error in the form of "red wavy line".

I refer to "custom exception class" to solve this problem, but I find this method does not work.

If there are someone knows how to do , I will be very happy, because it takes me a whole day

For example:

#include<iostream>
using namespace std;
int Fuction(int i , int j){  

    //code
}

int main(){
    Funciton(1,1);
    Funciton(0,0);
    //I don't want i or j is zero
    //But if they are still zero , The program will still work normally
    return 0;
}

CodePudding user response：

There is no integer type without a 0. However, you can provoke a compiler error by introducing a conversion to a pointer type. Its a bit hacky, but achieves what you want (I think) for a literal 0:

#include <iostream>

struct from_int {
    int value;
    from_int(int value) : value(value) {}
};

struct non_zero {
    int value;
    non_zero(int*) = delete;
    non_zero(from_int f) : value(f.value) {}
};

void bar(non_zero n) {
    int i = n.value; // cannot be 0
}

int main() {
    bar(non_zero(42));
    //bar(non_zero(0)); // compiler error
}

bar is the function that cannot be called with a 0 parameter. 0 can be converted to a pointer but that constructor has no definition. Any other int will pick the other constructor. Though it requires the caller to explicitly construct a non_zero because only one user defined conversion is taken into account.

If you want to throw an exception, thats a whole different story. You'd simply add a check in the function:

if (i == 0) throw my_custom_exception{"some error message"};

CodePudding user response：

If you are using only MSVC you can also take a look at Structured Annotation Language (SAL). It is described on MSDN.

For your case you might be interested in _In_range_(lb,ub). An example would be:

void f(_In_range_(1,300) int a, _In_range_(1, 2147483647) int b);

Please note that this will not prohibit calling f(0, 0) but code analysis will trigger a warning. That warning will be triggered also in cases where you call f(x,x) and the compiler knows that x is zero.

In the past I liked to use SAL as it makes the interface clearer and can help reveal errors because the compiler can check more semantics. But now with modern C und the CppCoreGuidelines I am trying to follow the guidelines and so normally I don't need SAL anymore.