how do atof, atoi, and atol work?

**jverkoey** · 04-24-2003

how do atof, atoi, and atol work?

I am trying to figure this out because I've noticed that sometimes when converting a string to a float, it messes up the number. For instance: I convert the string "33414132431.2" to a float (atof), and it turns the resulting value in to 33414132431.200001

This is NOT a good thing when you are trying to compare two results together, and they aren't the same because they have a messed up end value.....

I'm wondering if maybe it's just because I'm causing an overflow with a number that big.........well, just looking for some advise, no flaming.

**Perspective** · 04-24-2003

> "33414132431.2"

there is no exact floating point representation for 0.2
it is...
// pseudo-binary
0.0110 0110 0110 0110.... for ever and ever and ever.

kinda like 3.14159......

one way ive seen people account for this is to use a correction factor
ie.

Code:

#define ICK 0.0001
....

if(difference_in_numbers < ICK)
           close enough, must be equal
else
         to far apart, not equal

**jverkoey** · 04-24-2003

aah, i see, so it's not the function's fault then. Ok, that should be fine then. thanks

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