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c++structuresizeofpacking

How to calculate at runtime the maximum value allowed before datatype rollover?

I have the following structure:

struct Some_Struct {
    uint32_t a;
    int16_t  b;
    uint8_t  c;
};

struct Other_Struct {
    uint32_t a;
    uint32_t b;
    uint32_t c;
};

The variable size is being calculated as such:

uint32_t size = sizeof(Some_Struct) + sizeof(Other_Struct) * n;

My question is, given a sizeof Some_Struct and Other_Struct whose actual size is dependent on the platform, architecture, and packing, how can I at runtime determine the maximum number of n allowed before size rolls over?

Solution

  • You can use numeric_limits:

    uint32_t maximum_n = (std::numeric_limits<uint32_t>::max() - sizeof(Some_Struct))
                                / sizeof(Other_Struct);