Is there a custom or standard library that I can use with objective c to convert a decimal floating point value into Hexadecimal, Binary and Octal NSStrings?
I've been looking around a lot but can only find how to convert the other direction (from everything else into decimal), by using: double result = (double)strtoll(myHexString.UTF8String, NULL,16)
As for octal and hex, you can exploit the fact that you can format numbers in hex and octal using the %x and %o specifiers:
NSString* str=[NSString stringWithFormat: #"Hex: %x Octal: %o",14,14];
But this only for the integral part, so you can use integers.If you want also the decimal part, to obtain fixed points you need to implement the algorithm, same for binary.
In order to complement the previous answer, the format specifier %x allows to treat integer value only.
If you get a decimal value greater than the max integer value you can use long long to cast your double value by this way: NSString * hexString = [NSString stringWithFormat:#"%llx", (long long)doubleValue];
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What's the difference between float and double?
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I have an Objective-C project that needs to display numbers like 0.00000217, and very small numbers like that. Problem is, Objective-C is rounding this to the 6th decimal place so it displays as 0.000002. Is there a type to display more decimal places? My code:
float floatValueOfSmallNumber = [value floatValue];
[theLabel setText:[NSString stringWithFormat:#"%f", floatValueOfSmallNumber]];
Thanks!
While a float only has ~7 significant decimal digits, that's not the problem you are running up against here; 0.00000217 has only three significant digits, after all.
You are using the %f format specifier which is inherited from C and defined thus (7.21.6 Formatted input/output functions):
A double argument representing a floating-point number is converted to decimal notation in the style [−]ddd.ddd, where the number of digits after the decimal-point character is equal to the precision specification. If the precision is missing, it is taken as 6; if the precision is zero and the # flag is not specified, no decimal-point character appears. If a decimal-point character appears, at least one digit appears before it. The value is rounded to the appropriate number of digits.
Using double won't change this; instead, you need to change your format specifier. You can use %e or %g if you don't mind scientific notation, but another alternative would be to use a precision specifier: %.10f, for example, will print ten decimal digits.
Is there a way to use scientific notation in objective c and have it display three significant digits only? What I am current using is:
string = [NSString stringWithFormat:#"%e", floatNumber];
// floatNumber = 100000; string = 1.000000e+06
I just want string = 1.00e+06
Use the format specifier ".2" as follows:
string = [NSString stringWithFormat:#"%.2e", floatNumber];
From apple's documentation:
The format specifiers supported by the NSString formatting methods and CFString formatting functions follow the IEEE printf specification...
And from the IEEE printf specification, if you read under the Description section, you will find:
e, E
The double argument shall be converted in the style "[-]d.ddde±dd", where there is one digit before the radix character (which is non-zero if the argument is non-zero) and the number of digits after it is equal to the precision; if the precision is missing, it shall be taken as 6; if the precision is zero and no '#' flag is present, no radix character shall appear. The low-order digit shall be rounded in an implementation-defined manner. The E conversion specifier shall produce a number with 'E' instead of 'e' introducing the exponent. The exponent shall always contain at least two digits. If the value is zero, the exponent shall be zero.
I have a situation where I have lots of different double values, for example 1.00, 0.25 and 2.50. I would like to round these doubles so that they become 1, 0.25 and 2.5; in other words I want to remove any trailing 0's. Is there a way to do this?
At the moment I have been using %.2f, and I'm wondering if I can make use of this but adapt it in some way. Please can someone help me out?
As long as you're talking only about display, this is quite easy. The format specifier you want is %g:
The double argument shall be converted in the style f or e (or in the style F or E in the case of a G conversion specifier), with the precision specifying the number of significant digits [...] Trailing zeros shall be removed from the fractional portion of the result[...]
double twopointfive = 2.500;
double onepointzero = 1.0;
double pointtwofive = .25000000000;
NSLog(#"%g %f", twopointfive, twopointfive);
NSLog(#"%g %f", onepointzero, onepointzero);
NSLog(#"%g %f", pointtwofive, pointtwofive);
2011-12-06 21:27:59.180 TrailingZeroes[39506:903] 2.5 2.500000
2011-12-06 21:27:59.184 TrailingZeroes[39506:903] 1 1.000000
2011-12-06 21:27:59.185 TrailingZeroes[39506:903] 0.25 0.250000
The same format specifier can be used with an NSNumberFormatter, which will also give you some control over significant digits.
The trailing zeroes can't be removed from the way the number is stored in memory, of course.
I believe you want the %g format specifier to redact trailing zeros.
Not really rounding, but have you tried just %f it should only show the number of digits required rather then padding out the number.
My answer above is wrong, %g as others has stated is the right way to go.
The documentation for string formatters should help too. http://developer.apple.com/library/ios/#documentation/Cocoa/Conceptual/Strings/Articles/formatSpecifiers.html#//apple_ref/doc/uid/TP40004265
Here is a list of all the format specifiers that you can use...
%# Object
%d, %i signed int
%u unsigned int
%f float/double
%x, %X hexadecimal int
%o octal int
%zu size_t
%p pointer
%e float/double (in scientific notation)
%g float/double (as %f or %e, depending on value)
%s C string (bytes)
%S C string (unichar)
%.*s Pascal string (requires two arguments, pass pstr[0] as the first, pstr+1 as the second)
%c character
%C unichar
%lld long long
%llu unsigned long long
%Lf long double
I'm reading someone elses code and they are using %#-1 to format an integer. I can't find anything on Google since it ignores symbols. Anyone else had more experience at string formatting than me?
[NSString stringWithFormat:#"%#-1", subnumber]
Thanks!
According to the specification:
Each conversion specification is introduced by the '%' character, or by the character sequence "%n$", after which the following appear in sequence:
Zero or more flags (in any order), which modify the meaning of the conversion specification.
An optional minimum field width. If the converted value has fewer bytes than the field width, it shall be padded with spaces by default on the left; it shall be padded on the right if the left-adjustment flag ( '-' ), described below, is given to the field width. The field width takes the form of an asterisk ( '*' ), described below, or a decimal integer.
An optional precision that gives the minimum number of digits to appear for the d, i, o, u, x, and X conversion specifiers; the number of digits to appear after the radix character for the a, A, e, E, f, and F conversion specifiers; the maximum number of significant digits for the g and G conversion specifiers; or the maximum number of bytes to be printed from a string in the s [XSI] [Option Start] and S [Option End] conversion specifiers. The precision takes the form of a period ( '.' ) followed either by an asterisk ( '*' ), described below, or an optional decimal digit string, where a null digit string is treated as zero. If a precision appears with any other conversion specifier, the behavior is undefined.
An optional length modifier that specifies the size of the argument.
A conversion specifier character that indicates the type of conversion to be applied.
We're using a conversion of the first type, since there's no dollar sign in here. Note the words in sequence at the top of the above list. The # is a conversion specifier character (as mentioned here), which indicates that we should access the value passed in as an NSObject and read its description property. Since we've already reached the last bullet point, the format code actually ends after the # symbol, and as #Kevin Ballard pointed out, the -1 is parsed as literal text.
That's just going to print "NUM-1" (where NUM is the number). To give an example, if the number is 5, that will print "5-1".
When using format strings, any modifiers to the format token must occur before the format type specifier. In this case, that means any modifiers to the %# token must occur between the % and the # (though I'm not sure if there are actually any modifiers that %# accepts).
subnumber is probably object of class like NSNumber. Like we use %d for int, %f for float, %# is place holder for a refrence. In that case
NSNumber *subnumber = [NSNumber numberWithInt:5];
NSLog([NSString stringWithFormat:#"%#-1", subnumber]);
will print '5-1'
How can I have a two-digit integer in a a string, even if the integer is less than 10?
[NSString stringWithFormat:#"%d", 1] //should be #"01"
I believe that the stringWithFormat specifiers are the standard IEEE printf specifiers. Have you tried
[NSString stringWithFormat:#"%02d", 1];
Use the format string %02d. This specifies to format an integer with a minimum field-width of 2 characters and to pad the formatted values with 0 to meet that width. See man fprintf for all the gory details of format specifiers.
If you are formatting numbers for presentation to the user, though, you should really be using NSNumberFormatter. Different locales have wildly different expectations about how numbers should be formatted.
[NSString stringWithFormat:#"%00.02d", intValue]
This help me to convert 1 to 01.