How to represent float value in unsigned long

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I am developing a C++ application to write some float value to an EEPROM chip.
I am converting this float data to unsigned long and extracted each bit from long and write 32 bit to the memory.

Everything works fine, but when I assign an unsigned long value and read from float it changes in union. Is it correct I got 1.4013e-45 float value for unsgned 1

My code is

C++

typedef union
{
    float floatValue;
    unsigned long longValue;
} LONG_FLOAT_UNION;

LONG_FLOAT_UNION lfu;
lfu.longValue = 1;
lfu.floatValue //This variable prints 1.4013e-45

How i can effectively convert float to unsigned long and unsigned long to float without losing its decimal values. I cant multiply with float values to represent in unsigned long.

Posted 27-Jul-15 19:47pm

Arun Kumar K S

Updated 27-Jul-15 19:48pm

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Michael_Davies 28-Jul-15 2:22am

You need to understand how a float is mapped in memory, it is not as straight forward as a non-decimal number such as a long.

For a nice picture look at : http://stackoverflow.com/questions/6910115/how-to-represent-float-number-in-memory-in-c

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User 59241 · Answer 1 · 2015-07-27T20:57:00

I am not sure whether you don't understand unions or numbers. Floats and ints are different. A float is stored in IEEE 754 format: https://msdn.microsoft.com/en-us/library/0b34tf65.aspx[^]

To put this another way there is absolutely no correlation between what is stored in memory for a long int and what is stored for a float even if they occupy the same number of bytes. Your assumptions are false.

When you set the long int to 1 so setting the LSB that corresponds to a very small number in IEEE 754.

Test here: http://www.h-schmidt.net/FloatConverter/IEEE754.html[^]

It may be more illuminating to do this:

C++

lfu.floatValue = 1.0f;

and see what the long int value is.

If you can't use floats you will have to write your own code to do the task.

CPallini · Answer 2 · 2015-07-27T20:30:00

Solution 1

Quote:
Is it correct I got 1.4013e-45 float value for unsgned 1

Yes it is correct. You may try yourself it at this page (insert 1 in the hexadecimal or binary representation of the number and see the result).
Now we could better help if you state exactly your requirements.

Posted 27-Jul-15 20:30pm

CPallini