When I include the header file <string.h> in MS Visual Studio 2010 it says nothing , but when I declare a string variable in the main function or in any function , it gives an intellisense error that says that string is an undeclared identifier
What's the solution for that issue?
C doesn't actually have strings, at least not really. Unlike C++, strings are actually represented as character arrays, which MUST be null terminated '\0'. What the string header actually does is define functions to help you compare, copy, and modify strings.
Valid string definitions would include:
char string_one[ 80 ];
char *string_two = "this is a character string";
char *string_three = malloc( 80 * sizeof( char ) );
strcpy(string_three, "I have a string now");
There are a TON of resources for string usage in C, heres a few to get you started:
http://www.cs.nyu.edu/courses/spring05/V22.0201-001/c_tutorial/classes/String.html
http://www.eskimo.com/~scs/cclass/notes/sx8.html
http://en.wikipedia.org/wiki/C_string_handling
Related
Im wondering how to convert
NSString = "\xC4"; ....
to real NSString represented in normal format
Fundamentally related to xcode UTF-8 literals. Of course, it is ambiguous what you actually mean by "\xC4" - without an encoding specified, it means nothing.
If you mean the character whose Unicode code point is 0x00C4 then I would think (though I haven't tested) that this will do what you want.
NSString *s = #"\u00C4";
First are you sure you have \xC4 in your string? Consider:
NSString *one = #"\xC4\x80";
NSString *two = #"\\xC4\\x80";
NSLog(#"%# | %#", one, two);
This will output:
Ā | \xC4\x80
If you are certain your string contains the four characters \xC4 are you sure it is UTF-8 encoded as ASCII? Above you will see I added \x80, this is because \xC4 is not valid UTF-8, it is the first byte of a two-byte sequence. Maybe you have only shown a sample of your input and the second byte is present, if not you do not have UTF-8 encoded as ASCII.
If you are certain it is UTF-8 encoded as ASCII you will have to convert it yourself. It might seem the Cocoa string encoding methods would handle it, especially as what you appear to have is a string as it might be written in Objective-C source code. Unfortunately the obvious encoding, NSNonLossyAsciiStringEncoding only handles octal and unicode escapes, not the hexadecimal escapes in your string.
You can use any algorithm you like to convert it. One choice would be a simple finite state machine which scans the input a byte at a time and recognises the four byte sequence: \, x, hex-digit, hex-digit; and combines the two hex-digits into a single byte. NSString is not the best choice for byte-at-time string processing, you may be better off converting to C strings, e.g.:
// sample input, all characters should be ASCII
NSString *input = #"\\xC4\\x80";
// obtain a C string containing the ASCII characters
const char *cInput = [input cStringUsingEncoding:NSASCIIStringEncoding];
// allocate a buffer of the correct length for the result
char cOutput[strlen(c2a)+1];
// call your function to decode the hexadecimal escapes
convertAsciiEncodedUTF8(cInput, cOutput);
// create a NSString from the result
NSString *output = [NSString stringWithCString:cOutput encoding:NSUTF8StringEncoding];
You just need to write the finite state machine, or other algorithm, for convertAsciiEncodedUTF8.
(If you write an algorithm and it fails ask another question showing your code, somebody will probably help you. But don't expect someone to write it for you.)
HTH
I am new in programming. I have string NSString *string = #"\U0420\U043e\U0437\U044b"; and after each slash('\') i need put another slash to get string like this #"\\U0420\\U043e\\U0437\\U044b"
I am new to programming and objective-c. please help.
My original answer was:
Use [NSString stringByReplacingOccurrencesOfString:withString:] (reference).
NSString *string = #"\U0420\U043e\U0437\U044b";
NSString *converted = [string stringByReplacingOccurrencesOfString:#"\\"
withString:#"\\\\\\"];
However I now don't think that's right given the \ characters won't actually exist in string; instead the compiler will convert each of those sequences into a unicode character. You will need to encode string as this:
NSString *string = #"\\U0420\\U043e\\U0437\\U044b";
In order to use the above code. I cannot see any alternative to this.
Further Update: Often when I've come across questions like this there is a confusion between string literals and string data. In your question those \ characters won't appear as the compiler will have converted them into unicode characters (\Uxxx is a unicode escape sequence for a single character). However if you provided a string like that at runtime (say read from a text file) then those \ characters will exist and you can use the code above.
I am getting null character in the middle of the string obtained as a part of response to HTTP Post. As a result the content gets printed only upto the null character even though the string has more data in it. Below is the sample code that illustrates the problem
NSString *testString= #"v1db1���������¿¿sssss"; ->this line shows the null character warning
NSInteger stringlength = [testString length];
NSLog(#"String Length:%ld",stringlength);
NSLog(#"String Value:%#",testString);
Note: the test string contains a null character with the question mark. For some reason I am not able to save the post if I copy the exact string.
The first line shows a warning "Null character(s) preserved in string literal" in Xcode.
The output of this program is
String Length:21
String Value:v1db1
What is the correct approach to solve this problem?. I am thinking of scanning the NSString for any null character and removing the same. What could be the reason I am getting null character ?.
The problem characters are UTF-8 encoded something (EF BF BD and C2 BF) that are handled badly directly in quoted strings in XCode. You will need to convert it. Something like:
[ NSString stringWithUTF8String: [ #"v1db1���������¿¿sssss" cStringUsingEncoding: [ NSString defaultCStringEncoding ] ] ];
"strnset" is standard-c, (visual c++) and should work in objective-c.
But it doesn't recognize it.
What library am I missing? I have tried: stdio.h and string.h... both don't do it.
what would work in its place where I am given a char array and I want to create: n * characters to be placed in it?
example: _strnset(data, '8', 12); will yield -> data = "888888888888"
Use memset() instead. strnset is not part of the standard "C" library.
What property does strset have over memset that you are interested in?
NAME
memset -- fill a byte string with a byte value
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <string.h>
void *
memset(void *b, int c, size_t len);
DESCRIPTION
The memset() function writes len bytes of value c (converted to an
unsigned char) to the byte string b.
RETURN VALUES
The memset() function returns its first argument.
strnset is actually not a standard C function. It's not present in the GCC headers.
I need to use something like NSLog but without the timestamp and newline character, so I'm using printf. How can I use this with NSString?
You can convert an NSString into a UTF8 string by calling the UTF8String method:
printf("%s", [string UTF8String]);
//public method that accepts a string argument
- (void) sayThis : ( NSString* ) this
{
printf("%s",[this cString]);
}
According to the NSString.h ( html version ) the UTF8String method is only available on Mac OSX.
(see below )
All the other methods I looked at are marked as 'availability:Openstep'
There are further methods that will return regular char* strings but they might throw character conversion exceptions.
NOTE The string pointers point to memory that might go away so you have to copy the strings if you want to keep a copy of the string contents, but immediate printing should be fine ?
There are also methods that will return an encoded string, and a method to test if the encoding you want will work ( I think ) so you can check if your required encoding will work and then request a string that has been encoded as required.
From reading through the .h file itself there are many encodings and translations between encodings.
These are managed using enumerations so you can pass the type of encoding you want as an argument.
On linux etc. do :
locate NSString.h
** Note this found the html doc file also
otherwise do a :
find /usr -name NSString.h
NOTE Your mileage may vary :)
Thanks.
From the NSString.h html doc file :
cString
- (const char*) cString;
Availability: OpenStep
Returns a pointer to a null terminated string of 8-bit characters in the default encoding. The memory pointed to is not owned by the caller, so the caller must copy its contents to keep it. Raises an NSCharacterConversionException if loss of information would occur during conversion. (See -canBeConvertedToEncoding: .)
cStringLength
- (NSUInteger) cStringLength;
Availability: OpenStep
Returns length of a version of this unicode string converted to bytes using the default C string encoding. If the conversion would result in information loss, the results are unpredictable. Check -canBeConvertedToEncoding: first.
cStringUsingEncoding:
- (const char*) cStringUsingEncoding: (NSStringEncoding)encoding;
Availability: MacOS-X 10.4.0, Base 1.2.0
Returns a pointer to a null terminated string of characters in the specified encoding.
NB. under GNUstep you can used this to obtain a nul terminated utf-16 string (sixteen bit characters) as well as eight bit strings.
The memory pointed to is not owned by the caller, so the caller must copy its contents to keep it.
Raises an NSCharacterConversionException if loss of information would occur during conversion.
canBeConvertedToEncoding:
- (BOOL) canBeConvertedToEncoding: (NSStringEncoding)encoding;
Availability: OpenStep
Returns whether this string can be converted to the given string encoding without information loss.