Thread: atof() question

Hi all,

I am getting the following warning using the following code:

Code:

float Convert(char *str)
{
    float num;
    num=atof(str);
    return num;
}

warning C4244: '=' : conversion from 'double ' to 'float ', possible loss of data

I thought that atof() is ascii to float..... not asci to double........
What am I doing wrong?

Thank you

Code:

float Convert(char *str)
{
    float num;
    num = (float) atof(str);
    return num;
}

or

Code:

float Convert(char *str)
{
    float num;
    sscanf(str, "%f", &num);
    return num;
}

thank you for the code it's great!

I want to use float for study purpses.

Except the fact the float is 6 digit percision and double is 10,
I don't really understand the difference.

for example if I enter the following number 1234.56 in a float type the output will be 1234.560059 , I don't understand why.

Another thing if I use

Code:

num=(float)atof(string,"%f",&num);

In what point will I my data lost it's precision.

Many thanks again

for example if I enter the following number 1234.56 in a float type the output will be 1234.560059 , I don't understand why.

A simple answer is "because computers work in base 2 and we (humans) work in base 10". Some numbers who are representable with a finite numbers of digits in base 10 aren't necessarily representable with a finite numbers of digits in base 2.

Example. "2/3" can't be represented with a finite number of digit in base 10. If we can take only 4 digits to represent that number, we'll write "0.667". But in base 3, you can write it as "0.2".

Another thing if I use

Code:

num=(float)atof(string,"%f",&num);

In what point will I my data lost it's precision.

Doubles have more significative digits than floats. By the way, that call to atof is incorrect (mix between sscanf and atof).