There are some great answers here about how to format the decimal places of a float for a string:
float myFloatA = 2.123456f;
NSLog(#"myFloatA: [%.2f]", myFloatA;
// returns:
// myFloatA: [2.12]
But what I'm looking for is how to format the whole numbers of the same float. This can be done with the same sort of trick on an integer:
int myInt = 2;
NSLog(#"myInt: [%5d]", myInt;
// returns:
// myInt: [ 2]
So I was hoping something like a %5.2f would be the answer to formatting both before and after the decimal. But it doesn't:
float myFloatA = 2.123456f;
NSLog(#"myFloatA: [%5.2f]", myFloatA;
// returns:
// myFloatA: [2.12]
Any thoughts on this one?
Using the print specifiers is all very well for NSLogs, but think about this another way.
Usually, you want a string representation of a number when you are displaying it in something like a text field. In which case, you might as well use an NSNumberFormatter which does most of the heavy lifting for you.
Also confirmed that this works. If you're worried you're not getting 5 character width, try forcing zero padding with:
NSLog(#"myFloatA: [%05.2f]", myFloatA);
Related
Can any one please help me how to get float value as it is from text box
for Ex: I have entered 40.7
rateField=[[rateField text] floatValue];
I am getting rateField value as 40.7000008 but I want 40.7 only.
please help me.
thanks in advance
Thanks Every body,
I tried all the possibilities but I am not able to get what I want. I am not looking to print the value to convert into string.I want to use that value for computation. If i use Number Formatter again when i am converting from number to float it is giving same problem.So i want float value only but it should be whatever i have given in the text box it should not be padded with any values.This is my requirement.Please help me.
thanks®ards Balu
Thanks Every body,
I tried all the possibilities but I am not able to get what I want. I am not looking to print the value to convert into string.I want to use that value for computation. If i use Number Formatter again when i am converting from number to float it is giving same problem.So i want float value only but it should be whatever i have given in the text box it should not be padded with any values.This is my requirement.Please help me.
thanks®ards
Balu
This is ok. There is not guaranteed that you will get 40.7 if you will use even double.
If you want to output 40.7 you can use %.1f or NSNumberFormatter
Try using a double instead. Usually solves that issue. Has to do with the storage precision.
double dbl = [rateField.text doubleValue];
When using floating point numbers, these things can happen because of the way the numbers are stored in binary format in the computers memory.
It's similar to the way 1/3 = 0.33333333333333... in decimal numbers.
The best way to deal with this is to use number formatters in the textbox that displays the value.
You are already resolved float value.
Floating point numbers have limited precision. Although it depends on
the system, float relative error due to rounding will be around 1.1e-8
Non elementary arithmetic operations may give larger errors, and, of
course, error progragation must be considered when several operations
are compounded.
Additionally, rational numbers that are exactly representable as
floating point numbers in base 10, like 0.1 or 0.7, do not have an
exact representation as floating point numbers in base 2, which is
used internally, no matter the size of the mantissa. Hence, they
cannot be converted into their internal binary counterparts without a
small loss of precision. This can lead to confusing results: for
example, floor((0.1+0.7)*10) will usually return 7 instead of the
expected 8, since the internal representation will be something like
7.9999999999999991118....
So if you're using those numbers for output, you should use some rounding mechanism, even for double values.
i know this seems to be a stupid question, but i'm really getting trouble here.
I'm working in a project where i have some functions i can´t modify. That is, i got some C functions (not really my speciality) inside my Obj. C code that i can modify.
So here it is... to explain a little what i have.
I'm receiving a NSData like "\xce\x2d\x1e\x08\x08\xff\x7f" . I have to put each \hex code in a char array, like this:
cArray[1]=ce;
cArray[2]=2d;
cArray[3]=1e;
cArray[4]=08;
etc, etc... of course not LIKE THIS, but just so you understand. My initial move was to separe the NSData with subdataWithRange: and fill in an array with all "subdata". So the next move could be passing each position of that array to a char array, and that's where i got stuck.
I'm using something like (dont have my code right now)
for(int i=0 ; i<=64 ; i++) {
[[arrayOfSubData objectAtIndex:i] getBytes:&charArray[i]];
}
To fill the char array with the hex from my array of subData. That works almost perfectly. Almost.
Taking that example of cArray, my NSLog(#"pos%i: %x",i,charArray[i]) would show me:
pos1: ce
pos2: 2d
pos3: 1e
pos4: 8
And all the "left zeros" are supressed in that same way. My workaround for the moment (and i´m not sure if it is the best practice here) is to take my subDataArray and initWithFormat: a string with it. With that i can transform the string to an int with NSScanner scanHexInt:, but then i´m stucked again when converting back my decimal int to a hexadecimal CHAR. What would be the best approach to fill my char array that way?
Any help or some "tough love" will be greatly appreciated. Thanks
According to the normal rules of printf formatting (which NSLog follows also) you want the following:
NSLog(#"pos%i: %02x", i, charArray[i]);
The '0' says to left pad with 0s and is a flag. The '2' says to ensure that output for that field is at least two characters. So that'll ensure that at least two characters are output and pad to the left with '0's in order to fill space.
having a bit of trouble finding a solution to this.
I want to take a large ordered text file of words and create - in the same order - a text file of fixed length numeric values.
For example:
Input File Output File
AAA -> 00000001
AAH -> 00002718
AAZ -> 71827651
Initially it seemed a hash function would do the trick. However they are one way. Also perhaps they are a bit "heavyweight" for this. After all, I don't need any cryptography. Plus, it's a reference file. It will never change.
Any compression is a bonus not essential. That said, I don't want the file to get any bigger than it already is. Which is why I don't just want to write out the words as text but with fixed lengths.
So, bottom line; input is a NSString of variable length, output is an integer of fixed length. And, I must be able to take the integer and figure out the string.
Any help much appreciated!
Thanks!
xj
Well, this would be a bit of a brute force method, but here's my guess.
Start by making a custom function to convert one letter of text to an integer less than 100. (I'm not sure if such a function already exists, if so then great!) You might need to just go to stuff like "if ([input isEqual: #"a"]){ return 1;}
Then, run that function on each letter of text, and get the final integer by combining the previous results.
For example:
int myVal1 = [intConverter firstLetter];
int myVal2 = [intConverter secondLetter];
int myVal3 = [intConverter thirdLetter];
int finalValue =100^3 + 100^2*myVal1 + 100*myVal2 + myVal3;
Then, finalValue would be of the form 1(myVal1)(myVal2)(myVal3), which is what I think you're looking for.
To get back the original string, simply use the mod (%) and division functions to get the individual values back, then run the intConverter function backwards. (This would probably mean writing a new function that basically runs those if statements in reverse, but oh well.)
I hope this helps.
I here is the problem:
I have a NSString that contain "1.7" (for example) and I have to get the float number = 1.7
I' ve tried with [mystring floatValue] but the result is 1.700000000004576
If I try with "1.74" the result is 1.74000000000000000067484
how can I fix it?
thank you!
You are correctly converting the string into a float. The problem is that floating point numbers cannot represent all real numbers exactly. A direct assignment:
float x = 1.7;
will still have a precision error. That's just how floating point numbers are.
The workaround depends on your needs. Some examples: If you need more precision for mathematical calculations, you can use doubles. If you're trying to generate output for the user, you can format the output so it limits the number of digits shown after the decimal point. If you're dealing with money, you could convert floating point dollar amounts into integer numbers of cents and perform all calculations using integers, only showing a decimal point on output to the user.
Floats need to be able to represent infinitely many real numbers, but a float contains a finite number of bits, so floats are approximations.
See this article for more.
You can trim the answer by using the formatting below.
The .1 will set the result to one decimal place.
NSLog(#"mystring = %.1f ",[mystring floatValue]);
Solved!
I used sqlite3_bind_text even if my database attribute is FLOAT value and I used mystring instead of myfloat and it work fine! Thank you!
This is probably something very simple but I'm not getting the results I'm expecting. I apologise if it's a stupid question, I just don't what to google for.
Easiest way to explain is with some code:
int var = 2.0*4.0;
NSLog(#"%d", 2.0*4.0);//1
NSLog(#"%d", var);//2
if ((2.0*4.0)!=0) {//3
NSLog(#"true");
}
if (var!=0) {//4
NSLog(#"true");
}
This produces the following output:
0 //1
8 //2
true //3
true //4
The one that I don't understand is line //1. Why are all the others converting (I'm assuming the correct word is "casting", please correct me if I'm wrong) the float into an int, but inside NSLog it's not happening. Does this have something to do with the string formatting %d parameter and it being fussy (for lack of a better word)?
You're telling NSLog that you're passing it an integer with the #"%d" format specifier, but you're not actually giving it an integer; you're giving it a double-precision floating-point value (8.0, as it happens). When you lie to NSLog, its behavior is undefined, and you get unexpected results like this.
Don't lie to NSLog. If you want to convert the result of 2.0*4.0 to an integer before printing, you need to do that explicitly:
NSLog(#"%d", (int)(2.0*4.0));
If, instead, you want to print the result of 2.0*4.0 as a double-precision floating-point number, you need to use a different format specifier:
NSLog(#"%g", 2.0*4.0);
More broadly, this is true of any function that takes a variable number of arguments and some format string to tell it how to interpret them. It's up to you to make sure that the data you pass it matches the corresponding format specifiers; implicit conversions will not happen for you.
First, you never used floats in your program. They are doubles.
Second, the arguments of NSLog, printf and the likes are not automatically converted to what you specify using %d or %f. It follows the standard promotion rule for untyped arguments. See the ISO specification, sec 6.5.2.2.6 and 6.5.2.2.7. Note the super weird rule that inside these functions,
a float is automatically promoted to double,
and any integer smaller than an int is promoted to int. (see 6.3.1.1.2)
So, strictly speaking, the specification %f is not showing a float, but a double. See the same document, Sec. 7.19.6.1.8.
Note also that in your case 1 and 3, promotions are to double.
In examples 2, 3 and 4, the float is either being assigned to an int (which converts it) or compared with an int (which also converts it). In 1, however, you're passing the float as an argument to a function. The printf function allows all the arguments after the initial format string to be of any type, so this is valid. But since the compiler doesn't know you mean for it to be an int (remember, you haven't done anything to let the compiler know), the float is passed along as a floating-point value. When printf sees the %d formatting specifier, it pops enough bytes for an int from the argument list and interprets those bytes as an int. Those bytes happen to look like an integer 0.
The format string %d expects a decimal number, meaning a base 10 integer, not a floating point. What you want there is %f if you're trying to get it to print out 8.0
The first parameter to NSLog is a format string, then the second (and subsequent) parameters can be any types. The compiler doesn't know what the types should be at compile time and so doesn't try to cast them to anything. At run time NSLog assumes the second (and subsequent) parameters are as specified in the format string. If there's a mismatch unexpected and generally unhappy things happen.
Summary; Make sure you pass variables of the right type in the second (and subsequent) parameter.