I get a warning when I compile my code, and I'm not sure how to resolve it.
warning: incompatible integer to pointer conversion initializing
'unsigned long *' with an expression of type 'unsigned long
_Nullable'
NSDictionary *dict = #{#"foo": #420};
unsigned long *num = [[dict objectForKey:#"foo"] unsignedLongValue];
NSString *oct = [NSString stringWithFormat:#"%o", num];
NSLog(#"%04u", [oct intValue]); // 0644
The output is correct (I'm converting a number to octal format), but I guess my code isn't up to par with the compiler.
Two mistakes here -
1) unsigned long is not an object but primitive.
You simply need to remove the "*" before num as follow -
unsigned long num = [[dict objectForKey:#"foo"] unsignedLongValue];
2) The format of unsigned long is %lu and not %o as you mentioned.
NSString *oct = [NSString stringWithFormat:#"%lu", num];
So, the correct code should be -
NSDictionary *dict = #{#"foo": #420};
unsigned long num = [[dict objectForKey:#"foo"] unsignedLongValue];
NSString *oct = [NSString stringWithFormat:#"%lu", num];
NSLog(#"%04u", [oct intValue]); // 0644
I believe that this should work (the warnings went away):
unsigned long num = (unsigned long)[[dict objectForKey:#"foo"] unsignedLongValue];
NSString *oct = [NSString stringWithFormat:#"%lo", num];
Do you know how can i convert float value to nsstring value because with my code, there is an error.
My Code :
- (float)percent:(float)a :(float)b{
return a / b * 100;
}
- (void)objectLoader:(RKObjectLoader*)objectLoader didLoadObjects:(NSArray*)objects {
// ....
float tx_nb_demande_portabilite = [self percent: [(NSNumber*) [stat nb_demande_portabilite] floatValue] :[(NSNumber*) [stat nb_users] floatValue]];
NSString *tx_nb_demande_portabilite_st = [NSString stringWithFormat:#"%#", tx_nb_demande_portabilite];
//....
}
The error :
EXC_BAD ACCESS for NSString *tx_nb_demande_portabilite_st = [NSString stringWithFormat:#"%#", tx_nb_demande_portabilite];
Thank you for your help.
You need to use %f format specifier for float, not %#.
NSString *str = [NSString stringWithFormat:#"%f", myFloat];
To use specific number of digits after decimal use %.nf where n is number of digits after decimal point.
// 3 digits after decimal point
NSString *str = [NSString stringWithFormat:#"%.3f", myFloat];
Obj-C uses C printf style formatting. Please check printf man page for all other possible formatting.
one more option:
NSString * str = [NSNumber numberWithFloat:value].stringValue;
#"%f" sounds like more appropriate format string for float.
[NSString stringWithFormat:#"%f", tx_nb_demande_portabilite];
A modern (and less verbose) approach would be:
NSString *str = #(myFloat).description;
I need to convert two numbers to string in Objective-C.
One is a long number and the other is a float.
I searched on the internet for a solution and everyone uses stringWithFormat: but I can't make it work.
I try
NSString *myString = [NSString stringWithFormat: #"%f", floatValue]
for 12345678.1234 and get "12345678.00000" as output
and
NSString *myString = [NSString stringWithFormat: #"%d", longValue]
Can somebody show me how to use stringWithFormat: correctly?
This article discusses how to use various formatting strings to convert numbers/objects into NSString instances:
String Programming Guide: Formatting String Objects
Which use the formats specified here:
String Programming Guide: String Format Specifiers
For your float, you'd want:
[NSString stringWithFormat:#"%1.6f", floatValue]
And for your long:
[NSString stringWithFormat:#"%ld", longValue] // Use %lu for unsigned longs
But honestly, it's sometimes easier to just use the NSNumber class:
[[NSNumber numberWithFloat:floatValue] stringValue];
[[NSNumber numberWithLong:longValue] stringValue];
floatValue has to be a double. At least this compiles correctly and does what is expected on my machine
Floats can only store about 8 decimal digits and your number 12345678.1234 requires more precision than that, hence only about the 8 most significant digit are stored in a float.
double floatValue = 12345678.1234;
NSString *myString = [NSString stringWithFormat: #"%f", floatValue];
results in
2011-11-04 11:40:26.295 Test basic command line[7886:130b] floatValue = 12345678.123400
You should use NSNumberFormatter eg:
NSNumberFormatter * nFormatter = [[NSNumberFormatter alloc] init];
[nFormatter setNumberStyle:NSNumberFormatterDecimalStyle];
NSNumber *num = [nFormatter numberFromString:#"12345678.1234"];
[nFormatter release];
I am doing a Cocoa tutorial where I need to count the characters in a field, then output something like 'the_string_i_am_count' has 21 characters.
I have managed to get the string, count it, and output the count but I have no idea how to output the count along with the string and the other info.
How would I do this?
-(IBAction)countCharacters:(id)sender
{
//i had to connect this to the class also to make it get the value.
//NSString *string = [inputField stringValue];
//get the number of chars
NSUInteger length = [[inputField stringValue] length];
[outputField setIntValue:length]; //string];
//[outputField setStringValue: #"'s' has %d characters.", string, length];
}
Semi working code:
-(IBAction)countCharacters:(id)sender
{
//i had to connect this to the class also to make it get the value.
NSString *string = [inputField stringValue];
//get the number of chars
NSUInteger length = [[inputField stringValue] length];
[outputField setStringValue:[NSString stringWithFormat:#"'%s' has %d characters.", string, length]];
}
[outputField setStringValue:[NSString stringWithFormat:#"%# has %# characters.", string, length]];
I'm trying to use the BEncoding ObjC class to decode a .torrent file.
NSData *rawdata = [NSData dataWithContentsOfFile:#"/path/to/the.torrent"];
NSData *torrent = [BEncoding objectFromEncodedData:rawdata];
When I NSLog torrent I get the following:
{
announce = <68747470 3a2f2f74 6f727265 6e742e75 62756e74 752e636f 6d3a3639 36392f61 6e6e6f75 6e6365>;
comment = <5562756e 74752043 44207265 6c656173 65732e75 62756e74 752e636f 6d>;
"creation date" = 1225365524;
info = {
length = 732766208;
name = <7562756e 74752d38 2e31302d 6465736b 746f702d 69333836 2e69736f>;
"piece length" = 524288;
....
How do I convert the name into a NSString? I have tried..
NSData *info = [torrent valueForKey:#"info"];
NSData *name = [info valueForKey:#"name"];
unsigned char aBuffer[[name length]];
[name getBytes:aBuffer length:[name length]];
NSLog(#"File name: %s", aBuffer);
..which retrives the data, but seems to have additional unicode rubbish after it:
File name: ubuntu-8.10-desktop-i386.iso)
I have also tried (from here)..
NSString *secondtry = [NSString stringWithCharacters:[name bytes] length:[name length] / sizeof(unichar)];
..but this seems to return a bunch of random characters:
扵湵畴㠭ㄮⴰ敤歳潴⵰㍩㘸椮潳
The fact the first way (as mentioned in the Apple documentation) returns most of the data correctly, with some additional bytes makes me think it might be an error in the BEncoding library.. but my lack of knowledge about ObjC is more likely to be at fault..
That's an important point that should be re-emphasized I think. It turns out that,
NSString *content = [NSString stringWithUTF8String:[responseData bytes]];
is not the same as,
NSString *content = [[NSString alloc] initWithBytes:[responseData bytes]
length:[responseData length] encoding: NSUTF8StringEncoding];
the first expects a NULL terminated byte string, the second doesn't. In the above two cases content will be NULL in the first example if the byte string isn't correctly terminated.
How about
NSString *content = [[[NSString alloc] initWithData:myData
encoding:NSUTF8StringEncoding] autorelease];
NSData *torrent = [BEncoding objectFromEncodedData:rawdata];
When I NSLog torrent I get the following:
{
⋮
}
That would be an NSDictionary, then, not an NSData.
unsigned char aBuffer[[name length]];
[name getBytes:aBuffer length:[name length]];
NSLog(#"File name: %s", aBuffer);
..which retrives the data, but seems to have additional unicode rubbish after it:
File name: ubuntu-8.10-desktop-i386.iso)
No, it retrieved the filename just fine; you simply printed it incorrectly. %s takes a C string, which is null-terminated; the bytes of a data object are not null-terminated (they are just bytes, not necessarily characters in any encoding, and 0—which is null as a character—is a perfectly valid byte). You would have to allocate one more character, and set the last one in the array to 0:
size_t length = [name length] + 1;
unsigned char aBuffer[length];
[name getBytes:aBuffer length:length];
aBuffer[length - 1] = 0;
NSLog(#"File name: %s", aBuffer);
But null-terminating the data in an NSData object is wrong (except when you really do need a C string). I'll get to the right way in a moment.
I have also tried […]..
NSString *secondtry = [NSString stringWithCharacters:[name bytes] length:[name length] / sizeof(unichar)];
..but this seems to return random Chinese characters:
扵湵畴㠭ㄮⴰ敤歳潴⵰㍩㘸椮潳
That's because your bytes are UTF-8, which encodes one character in (usually) one byte.
unichar is, and stringWithCharacters:length: accepts, UTF-16. In that encoding, one character is (usually) two bytes. (Hence the division by sizeof(unichar): it divides the number of bytes by 2 to get the number of characters.)
So you said “here's some UTF-16 data”, and it went and made characters from every two bytes; each pair of bytes was supposed to be two characters, not one, so you got garbage (which turned out to be mostly CJK ideographs).
You answered your own question pretty well, except that stringWithUTF8String: is simpler than stringWithCString:encoding: for UTF-8-encoded strings.
However, when you have the length (as you do when you have an NSData), it is even easier—and more proper—to use initWithBytes:length:encoding:. It's easier because it does not require null-terminated data; it simply uses the length you already have. (Don't forget to release or autorelease it.)
A nice quick and dirty approach is to use NSString's stringWithFormat initializer to help you out. One of the less-often used features of string formatting is the ability to specify a mximum string length when outputting a string. Using this handy feature allows you to convert NSData into a string pretty easily:
NSData *myData = [self getDataFromSomewhere];
NSString *string = [NSString stringWithFormat:#"%.*s", [myData length], [myData bytes]];
If you want to output it to the log, it can be even easier:
NSLog(#"my Data: %.*s", [myData length], [myData bytes]);
Aha, the NSString method stringWithCString works correctly:
With the bencoding.h/.m files added to your project, the complete .m file:
#import <Foundation/Foundation.h>
#import "BEncoding.h"
int main (int argc, const char * argv[]) {
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
// Read raw file, and de-bencode
NSData *rawdata = [NSData dataWithContentsOfFile:#"/path/to/a.torrent"];
NSData *torrent = [BEncoding objectFromEncodedData:rawdata];
// Get the file name
NSData *infoData = [torrent valueForKey:#"info"];
NSData *nameData = [infoData valueForKey:#"name"];
NSString *filename = [NSString stringWithCString:[nameData bytes] encoding:NSUTF8StringEncoding];
NSLog(#"%#", filename);
[pool drain];
return 0;
}
..and the output:
ubuntu-8.10-desktop-i386.iso
In cases where I don't have control over the data being transformed into a string, such as reading from the network, I prefer to use NSString -initWithBytes:length:encoding: so that I'm not dependent upon having a NULL terminated string in order to get defined results. Note that Apple's documentation says if cString is not a NULL terminated string, that the results are undefined.
Use a category on NSData:
NSData+NSString.h
#interface NSData (NSString)
- (NSString *)toString;
#end
NSData+NSString.m
#import "NSData+NSString.h"
#implementation NSData (NSString)
- (NSString *)toString
{
Byte *dataPointer = (Byte *)[self bytes];
NSMutableString *result = [NSMutableString stringWithCapacity:0];
NSUInteger index;
for (index = 0; index < [self length]; index++)
{
[result appendFormat:#"0x%02x,", dataPointer[index]];
}
return result;
}
#end
Then just NSLog(#"Data is %#", [nsData toString])"
You can try this. Fine with me.
DLog(#"responeData: %#", [[[NSString alloc] initWithBytes:[data bytes] length:[data length] encoding:NSASCIIStringEncoding] autorelease]);
Sometimes you need to create Base64 encoded string from NSData. For instance, when you create a e-mail MIME. In this case use the following:
#import "NSData+Base64.h"
NSString *string = [data base64EncodedString];
This will work.
NSString *str = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];