Ask questions about the string conversion float

NSString * str = @ "4.03";
float f = [str floatValue];

Why f is 4.030000002 behind where so many decimal places?
Or ask how to convert after 4.03
Reply:
long tmp = f * 1000 ;/ / magnification of 1000 after taking decimal three
f = tmp / 1000.0;

Reply:

cited a floor LazyDreamHunter reply:

long tmp = f * 1000 ;/ / magnification of 1000 after taking decimal three
f = tmp / 1000.0;

The result is 4, not 4.03, but this felt Rao circle, ask what methods do
Reply:
float f = 4.3020003;
long tmp = f * 1000;
f = tmp / 1000.0;
cout << f << endl;
Do not forget / 1000.0 is not in addition to 1000, except for 1000 will be 4

This is the easiest way
Reply:
If you are the output, you can use sprintf ("% .3 f", f);
Reply:
printf ("% .3 f", f);
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Hello, the result was divided by 1000.0 4.0300002
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references, 4th Floor LazyDreamHunter reply:

If you are the output, you can use sprintf ("% .3 f", f);

Not output, I was saved to the variable inside, behind the operation to be performed.
Reply:
long tmp = f * 1000; This is the key, first converted to plastic, remove the fractional part of the
Reply:
f = tmp / 1000.0;
Reply:

reference to the 8th floor LazyDreamHunter reply:

long tmp = f * 1000; This is the key, first converted to plastic, remove the fractional part

Yes, my test code
NSString * s = @ "4.03";
float f = [s floatValue];
long l = f * 1000;
f = l / 1000.0;
By breakpoints, f is 4.0300002
Reply:
According to my way of doing certainly no problem, if you are afraid of overflow to 64 of the best plastic

quint64 tmp = f * 1000;
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What is your development environment
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I vc + +6.0 / / gcc is 4.03
Reply:

reference to the 13th floor LazyDreamHunter reply:

I vc + +6.0 / / gcc is 4.03

I was xcode5, iOS sdk7.0
Reply:
4.302
Press any key to continue

This is my vc6.0 output

# Include
# Include
void main ()
{
float f = 4.3020003;
long tmp = f * 1000;
f = tmp / 1000.0;
/ / Printf ("% .3 f", f);
cout << f << endl;

}
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L see whether you are tuning 4302
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Or 4.0300002
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That explanation or statement in front of the floating-point l, ah, how not an integer
Reply:
Forced conversion try, long tmp = (long) (f * 1000);
Reply:

 
/ / Use sprintf and sscanf achieve it. 
char buf [256]; 
float f = 4.030002; 
snprintf (buf, sizeof (buf), "% .3 f", f) ;/ / The key is to use the format function 
 snprintfsscanf (buf, "% f", & f);