C++ Convert 4 Hex Values to Float

Question

I am trying to convert 4 Hex Values to a float. The Hex Values are for example 3F A0 00 00. In binary representation they would correspond to 00111111 10100000 00000000 00000000. If these 4 binary values are interpreted as one 32-bit float (accordingly to IEEE754) the decimal value of the float should be 1,25. However i am struggling to automaticaly make the conversion from hex values to decimal float in C++ (I am using Qt as Framework).

Can anybody help me please?

Thanks!

question from:https://stackoverflow.com/questions/65920107/c-convert-4-hex-values-to-float

Answer 1

#include <iostream>
#include <cstring>
using namespace std;

int main()
{
    unsigned char bytes[] = {0x3F, 0xA0, 0x00, 0x00};
    
    uint32_t x = bytes[0];
    for (int i = 1; i < std::size(bytes); ++i) x = (x << 8) | bytes[i];

    static_assert(sizeof(float) == sizeof(uint32_t), "Float and uint32_t size dont match. Check another int type");
    
    float f{};
    memcpy(&f, &x, sizeof(x));
    // or since C++20 if available: float f = std::bit_cast<float>(x)
    
    cout << "f = " << f << endl;
}

Live