CODEWITHSUNDEEP
cfloating-pointbinaryhex
Dylan Holmes
Dylan Holmes

Reputation: 123

C Provide float with binary bits produces the wrong number

So, in C I am trying to give a floating point variable a number in binary bits (or hexadecimal digits) and then print it out, however it doesn't want to print the number I have calculated by hand or with an online converter.

float x = (float) 0b01000001110010000000000000000000;

or 

float x = (float) 0x41C80000;

When printed out using

printf("%f", x);

produces results like this:

1103626240.000000

Instead of the expected 25, due to a sign bit of 0, exponent bit of 131, and a fraction of 1.5625.

Why is this, and how can I get the results I want?

Upvotes: 0

Views: 183

Answers (1)

medalib
medalib

Reputation: 937

The value 0x41C80000 in hex, is an integer that has the value 1103626240 in decimal. In your code, you are casting this value to a float which gives you this result:

x = 1103626240.000000

A solution for this can be made using a union:

union uint_to_float {
    unsigned int u;
    float f;
};

union uint_to_float u2f;
u2f.u = 0x41C80000;
printf("x = %f\n", u2f.f);

EDIT: As mentioned by @chux, using uint32_t from stdint.h, instead of unsigned int is a better solution.

Upvotes: 3

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