Return value undefined in C
Not sure if I'm thinking about this, but how do I return something undefined when the parameter is not in the range it should be?
I am trying to do:
uint64_t function(uint64_t Value, uint64_t N) {
uint64_t result = 0;
if (N > 0){
//do something;
return result;
}
else{
return result is undefined;
}
}
How do I return N: undefined?
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One solution is to return the status and use the OUT parameter like this:
bool function(uint64_t Value, uint64_t N, uint64_t *result) {
if (N > 0){
//do something;
*result = 31337;
return true;
}
else{
return false;
}
}
Then, when you call this function, you check that the function returns true before using the result.
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For integer types, you can't.
There are exactly 2 64 possible values of the type uint64_t
, and each of them is a valid integer value.
In some cases, you can pick one value (perhaps UINT64_MIN
) that can be considered an error indication and return that, but this is not always practical.
Or you can revert the function to a success or failure result and pass the value uint64_t
back to the caller by other means, perhaps storing it with a pointer passed by the caller.
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Another option is to return the structure. This works better in C ++ (see Boost Optional), but here's the C version:
#include <stdio.h>
#include <stdbool.h>
struct optional_int {
bool valid;
int value;
};
struct optional_int f(int x)
{
struct optional_int result = {false, 0};
if(x > 0 && x < 10) {
result.valid = true;
result.value = x * 1024;
}
return result;
}
int main()
{
struct optional_int v;
v = f(9);
if(v.valid) {
printf("Result is %d\n", v.value);
}
return 0;
}
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